Update README and bump version to 0.3

Add async method for Userdata

Cargo.toml

@@ -1,13 +1,13 @@
 [package]
 name = "mlua"
-version = "0.2.2"
+version = "0.3.0-alpha.1"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>", "kyren <catherine@chucklefish.org>"]
 edition = "2018"
 repository = "https://github.com/khvzak/mlua"
 documentation = "https://docs.rs/mlua"
 readme = "README.md"
-keywords = ["lua", "luajit"]
-categories = ["api-bindings"]
+keywords = ["lua", "luajit", "async", "futures"]
+categories = ["api-bindings", "asynchronous"]
 license = "MIT"
 links = "lua"
 build = "build/main.rs"
@@ -31,22 +31,39 @@ lua52 = []
 lua51 = []
 luajit = []
 vendored = ["lua-src", "luajit-src"]
+async = ["futures-core", "futures-task", "futures-util"]
 
 [dependencies]
-num-traits = { version = "0.2.6" }
 bstr = { version = "0.2", features = ["std"], default_features = false }
+num-traits = { version = "0.2.11" }
+futures-core = { version = "0.3.4", optional = true }
+futures-task = { version = "0.3.4", optional = true }
+futures-util = { version = "0.3.4", optional = true }
 
 [build-dependencies]
 cc = { version = "1.0" }
-pkg-config = { version = "0.3.11" }
+pkg-config = { version = "0.3.17" }
 lua-src = { version = "535.0.1", optional = true }
 luajit-src = { version = "210.0.0", optional = true }
 
 [dev-dependencies]
-rustyline = "5.0"
-criterion = "0.2.0"
+rustyline = "6.0"
+criterion = "0.3"
 trybuild = "1.0"
+hyper = "0.13"
+tokio = { version = "0.2.18", features = ["full"] }
+futures-executor = "0.3.4"
+futures-util = "0.3.4"
+futures-timer = "3.0"
 
 [[bench]]
 name = "benchmark"
 harness = false
+
+[[example]]
+name = "async_tcp_server"
+required-features = ["async"]
+
+[[example]]
+name = "async_http_client"
+required-features = ["async"]

README.md

@@ -18,6 +18,14 @@ modules in Rust.
 
 ## Usage
 
+### Async
+
+Starting from 0.3, mlua supports async/await for all Lua versions. This feature works using Lua [coroutines](https://www.lua.org/manual/5.3/manual.html#2.6) and require running [Thread](https://docs.rs/mlua/latest/mlua/struct.Thread.html).
+
+**Examples**:
+- [HTTP Client](examples/async_http_client.rs)
+- [TCP Server](examples/async_tcp_server.rs)
+
 ### Choosing Lua version
 
 The following features could be used to choose Lua version: `lua53` (default), `lua52`, `lua51` and `luajit`.
@@ -41,7 +49,7 @@ Add to `Cargo.toml` :
 
 ``` toml
 [dependencies]
-mlua = "0.2"
+mlua = "0.3"
 ```
 
 `main.rs`
@@ -73,8 +81,8 @@ Add to `Cargo.toml` :
 crate-type = ["cdylib"]
 
 [dependencies]
-mlua = "0.2"
-mlua_derive = "0.2"
+mlua = "0.3"
+mlua_derive = "0.3"
 ```
 
 `lib.rs` :

build/main.rs

@@ -81,6 +81,10 @@ fn main() {
     #[cfg(all(feature = "lua51", feature = "luajit"))]
     panic!("You can enable only one of the features: lua53, lua52, lua51, luajit");
 
+    // Async
+    // #[cfg(all(feature = "async", not(any(feature = "lua53", feature = "lua52"))))]
+    // panic!("You can enable async only for: lua53, lua52");
+
     let include_dir = find::probe_lua();
     build_glue(&include_dir);
 }

examples/async_http_client.rs

@@ -0,0 +1,52 @@
+use std::collections::HashMap;
+
+use hyper::Client as HyperClient;
+
+use mlua::{Lua, Result, Thread, Error};
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    let lua = Lua::new();
+
+    let fetch_url = lua.create_async_function(|lua, uri: String| async move {
+        let client = HyperClient::new();
+        let uri = uri.parse().map_err(Error::external)?;
+        let resp = client.get(uri).await.map_err(Error::external)?;
+
+        let lua_resp = lua.create_table()?;
+        lua_resp.set("status", resp.status().as_u16())?;
+
+        let mut headers = HashMap::new();
+        for (key, value) in resp.headers().iter() {
+            headers.entry(key.as_str()).or_insert(Vec::new()).push(value.to_str().unwrap());
+        }
+        lua_resp.set("headers", headers)?;
+
+        let buf = hyper::body::to_bytes(resp).await.map_err(Error::external)?;
+        lua_resp.set("body", String::from_utf8_lossy(&buf).into_owned())?;
+
+        Ok(lua_resp)
+    })?;
+
+    let globals = lua.globals();
+    globals.set("fetch_url", fetch_url)?;
+
+    let thread = lua
+        .load(
+            r#"
+            coroutine.create(function ()
+                local res = fetch_url("http://httpbin.org/ip");
+                print(res.status)
+                for key, vals in pairs(res.headers) do
+                    for _, val in ipairs(vals) do
+                        print(key..": "..val)
+                    end
+                end
+                print(res.body)
+            end)
+        "#,
+        )
+        .eval::<Thread>()?;
+
+    thread.into_async(()).await
+}

examples/async_tcp_server.rs

@@ -0,0 +1,103 @@
+use std::net::Shutdown;
+use std::rc::Rc;
+
+use bstr::BString;
+use tokio::net::{TcpListener, TcpStream};
+use tokio::prelude::*;
+use tokio::sync::Mutex;
+use tokio::task;
+
+use mlua::{Function, Lua, Result, Thread, UserData, UserDataMethods};
+
+#[derive(Clone)]
+struct LuaTcpListener(Option<Rc<Mutex<TcpListener>>>);
+
+#[derive(Clone)]
+struct LuaTcpStream(Rc<Mutex<TcpStream>>);
+
+impl UserData for LuaTcpListener {
+    fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+        methods.add_async_function("bind", |_, addr: String| async {
+            let listener = TcpListener::bind(addr).await?;
+            Ok(LuaTcpListener(Some(Rc::new(Mutex::new(listener)))))
+        });
+
+        methods.add_async_method("accept", |_, listener, ()| async {
+            let (stream, _) = listener.0.unwrap().lock().await.accept().await?;
+            Ok(LuaTcpStream(Rc::new(Mutex::new(stream))))
+        });
+    }
+}
+
+impl UserData for LuaTcpStream {
+    fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+        methods.add_async_method("peer_addr", |_, stream, ()| async move {
+            Ok(stream.0.lock().await.peer_addr()?.to_string())
+        });
+
+        methods.add_async_method("read", |_, stream, size: usize| async move {
+            let mut buf = vec![0; size];
+            let mut stream = stream.0.lock().await;
+            let n = stream.read(&mut buf).await?;
+            buf.truncate(n);
+            Ok(BString::from(buf))
+        });
+
+        methods.add_async_method("write", |_, stream, data: BString| async move {
+            let mut stream = stream.0.lock().await;
+            let n = stream.write(&data).await?;
+            Ok(n)
+        });
+
+        methods.add_async_method("close", |_, stream, ()| async move {
+            stream.0.lock().await.shutdown(Shutdown::Both)?;
+            Ok(())
+        });
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    let lua = Lua::new();
+
+    let globals = lua.globals();
+    globals.set("tcp", LuaTcpListener(None))?;
+
+    globals.set(
+        "spawn",
+        lua.create_function(move |lua: &Lua, func: Function| {
+            let fut = lua.create_thread(func)?.into_async::<_, ()>(());
+            task::spawn_local(async move { fut.await.unwrap() });
+            Ok(())
+        })?,
+    )?;
+
+    let thread = lua
+        .load(
+            r#"
+            coroutine.create(function ()
+                local listener = tcp.bind("0.0.0.0:1234")
+                print("listening on 0.0.0.0:1234")
+                while true do
+                    local stream = listener:accept()
+                    print("connected from " .. stream:peer_addr())
+                    spawn(function()
+                        while true do
+                            local data = stream:read(100)
+                            data = data:match("^%s*(.-)%s*$") -- trim
+                            print(data)
+                            stream:write("got: "..data.."\n")
+                            if data == "exit" then
+                                stream:close()
+                                break
+                            end
+                        end
+                    end)
+                end
+            end)
+        "#,
+        )
+        .eval::<Thread>()?;
+
+    thread.into_async(()).await
+}

examples/guided_tour.rs

@@ -164,34 +164,6 @@ fn main() -> Result<()> {
             < f32::EPSILON
     );
 
-    // Normally, Rust types passed to `Lua` must be `Send`, because `Lua` itself is `Send`, and
-    // must be `'static`, because there is no way to be sure of their lifetime inside the Lua
-    // state.  There is, however, a limited way to lift both of these requirements.  You can
-    // call `Lua::scope` to create userdata and callbacks types that only live for as long
-    // as the call to scope, but do not have to be `Send` OR `'static`.
-
-    {
-        let mut rust_val = 0;
-
-        lua.scope(|scope| {
-            // We create a 'sketchy' Lua callback that holds a mutable reference to the variable
-            // `rust_val`.  Outside of a `Lua::scope` call, this would not be allowed
-            // because it could be unsafe.
-
-            lua.globals().set(
-                "sketchy",
-                scope.create_function_mut(|_, ()| {
-                    rust_val = 42;
-                    Ok(())
-                })?,
-            )?;
-
-            lua.load("sketchy()").exec()
-        })?;
-
-        assert_eq!(rust_val, 42);
-    }
-
     // We were able to run our 'sketchy' function inside the scope just fine.  However, if we
     // try to run our 'sketchy' function outside of the scope, the function we created will have
     // been invalidated and we will generate an error.  If our function wasn't invalidated, we

mlua_derive/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "mlua_derive"
-version = "0.2.0"
-authors = ["Aleksandr Orlenko <zxteam@protonmail.com>"]
+version = "0.3.0-alpha.1"
+authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
 edition = "2018"
 description = "Procedural macros for the mlua crate."
 repository = "https://github.com/khvzak/mlua"

src/conversion.rs

@@ -122,7 +122,7 @@ impl<'lua> FromLua<'lua> for AnyUserData<'lua> {
     }
 }
 
-impl<'lua, T: 'static + Send + UserData> ToLua<'lua> for T {
+impl<'lua, T: 'static + UserData> ToLua<'lua> for T {
     fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::UserData(lua.create_userdata(self)?))
     }
@@ -167,7 +167,7 @@ impl<'lua> ToLua<'lua> for bool {
 }
 
 impl<'lua> FromLua<'lua> for bool {
-    fn from_lua(v: Value, _: &'lua Lua) -> Result<Self> {
+    fn from_lua(v: Value<'lua>, _: &'lua Lua) -> Result<Self> {
         match v {
             Value::Nil => Ok(false),
             Value::Boolean(b) => Ok(b),
@@ -183,7 +183,7 @@ impl<'lua> ToLua<'lua> for LightUserData {
 }
 
 impl<'lua> FromLua<'lua> for LightUserData {
-    fn from_lua(value: Value, _: &'lua Lua) -> Result<Self> {
+    fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
         match value {
             Value::LightUserData(ud) => Ok(ud),
             _ => Err(Error::FromLuaConversionError {

src/error.rs

@@ -1,8 +1,11 @@
 use std::error::Error as StdError;
 use std::fmt;
+use std::io::Error as IoError;
+use std::net::AddrParseError;
+use std::rc::Rc;
 use std::result::Result as StdResult;
+use std::str::Utf8Error;
 use std::string::String as StdString;
-use std::sync::Arc;
 
 /// Error type returned by `mlua` methods.
 #[derive(Debug, Clone)]
@@ -115,7 +118,7 @@ pub enum Error {
         /// Lua call stack backtrace.
         traceback: StdString,
         /// Original error returned by the Rust code.
-        cause: Arc<Error>,
+        cause: Rc<Error>,
     },
     /// A custom error.
     ///
@@ -124,7 +127,7 @@ pub enum Error {
     /// Returning `Err(ExternalError(...))` from a Rust callback will raise the error as a Lua
     /// error. The Rust code that originally invoked the Lua code then receives a `CallbackError`,
     /// from which the original error (and a stack traceback) can be recovered.
-    ExternalError(Arc<dyn StdError + Send + Sync>),
+    ExternalError(Rc<dyn StdError>),
 }
 
 /// A specialized `Result` type used by `mlua`'s API.
@@ -203,7 +206,7 @@ impl StdError for Error {
 }
 
 impl Error {
-    pub fn external<T: Into<Box<dyn StdError + Send + Sync>>>(err: T) -> Error {
+    pub fn external<T: Into<Box<dyn StdError>>>(err: T) -> Error {
         Error::ExternalError(err.into().into())
     }
 }
@@ -214,7 +217,7 @@ pub trait ExternalError {
 
 impl<E> ExternalError for E
 where
-    E: Into<Box<dyn StdError + Send + Sync>>,
+    E: Into<Box<dyn StdError>>,
 {
     fn to_lua_err(self) -> Error {
         Error::external(self)
@@ -233,3 +236,21 @@ where
         self.map_err(|e| e.to_lua_err())
     }
 }
+
+impl std::convert::From<AddrParseError> for Error {
+    fn from(err: AddrParseError) -> Self {
+        Error::external(err)
+    }
+}
+
+impl std::convert::From<IoError> for Error {
+    fn from(err: IoError) -> Self {
+        Error::external(err)
+    }
+}
+
+impl std::convert::From<Utf8Error> for Error {
+    fn from(err: Utf8Error) -> Self {
+        Error::external(err)
+    }
+}

src/lib.rs

@@ -49,7 +49,6 @@ mod ffi;
 mod function;
 mod lua;
 mod multi;
-mod scope;
 mod stdlib;
 mod string;
 mod table;
@@ -65,7 +64,6 @@ pub use crate::error::{Error, ExternalError, ExternalResult, Result};
 pub use crate::function::Function;
 pub use crate::lua::{Chunk, Lua};
 pub use crate::multi::Variadic;
-pub use crate::scope::Scope;
 pub use crate::stdlib::StdLib;
 pub use crate::string::String;
 pub use crate::table::{Table, TablePairs, TableSequence};
@@ -74,4 +72,7 @@ pub use crate::types::{Integer, LightUserData, Number, RegistryKey};
 pub use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataMethods};
 pub use crate::value::{FromLua, FromLuaMulti, MultiValue, Nil, ToLua, ToLuaMulti, Value};
 
+#[cfg(feature = "async")]
+pub use crate::thread::AsyncThread;
+
 pub mod prelude;

src/lua.rs

@@ -3,34 +3,44 @@ use std::cell::{RefCell, UnsafeCell};
 use std::collections::HashMap;
 use std::ffi::CString;
 use std::marker::PhantomData;
-use std::os::raw::{c_char, c_int, c_void};
-use std::sync::{Arc, Mutex};
+use std::os::raw::{c_char, c_int};
+use std::rc::Rc;
 use std::{mem, ptr, str};
 
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::function::Function;
-use crate::scope::Scope;
 use crate::stdlib::StdLib;
 use crate::string::String;
 use crate::table::Table;
 use crate::thread::Thread;
 use crate::types::{Callback, Integer, LightUserData, LuaRef, Number, RegistryKey};
 use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataMethods};
-#[cfg(any(feature = "lua51", feature = "luajit"))]
-use crate::util::set_main_state;
 use crate::util::{
-    assert_stack, callback_error, check_stack, get_main_state, get_userdata, get_wrapped_error,
-    init_error_registry, init_userdata_metatable, pop_error, protect_lua, protect_lua_closure,
-    push_string, push_userdata, push_wrapped_error, userdata_destructor, StackGuard,
+    assert_stack, callback_error, check_stack, get_gc_userdata, get_main_state,
+    get_meta_gc_userdata, get_wrapped_error, init_error_registry, init_gc_metatable_for,
+    init_userdata_metatable, pop_error, protect_lua, protect_lua_closure, push_gc_userdata,
+    push_meta_gc_userdata, push_string, push_userdata, push_wrapped_error, StackGuard,
 };
 use crate::value::{FromLua, FromLuaMulti, MultiValue, Nil, ToLua, ToLuaMulti, Value};
 
+#[cfg(feature = "async")]
+use {
+    crate::types::AsyncCallback,
+    futures_core::future::LocalBoxFuture,
+    futures_task::noop_waker,
+    futures_util::future::{self, FutureExt, TryFutureExt},
+    std::{
+        future::Future,
+        task::{Context, Poll, Waker},
+    },
+};
+
 /// Top level Lua struct which holds the Lua state itself.
 pub struct Lua {
     pub(crate) state: *mut ffi::lua_State,
     main_state: *mut ffi::lua_State,
-    extra: Arc<RefCell<ExtraData>>,
+    extra: Rc<RefCell<ExtraData>>,
     ephemeral: bool,
     // Lua has lots of interior mutability, should not be RefUnwindSafe
     _no_ref_unwind_safe: PhantomData<UnsafeCell<()>>,
@@ -39,7 +49,7 @@ pub struct Lua {
 // Data associated with the lua_State.
 struct ExtraData {
     registered_userdata: HashMap<TypeId, c_int>,
-    registry_unref_list: Arc<Mutex<Option<Vec<c_int>>>>,
+    registry_unref_list: Rc<RefCell<Option<Vec<c_int>>>>,
 
     ref_thread: *mut ffi::lua_State,
     ref_stack_size: c_int,
@@ -47,7 +57,10 @@ struct ExtraData {
     ref_free: Vec<c_int>,
 }
 
-unsafe impl Send for Lua {}
+#[cfg(feature = "async")]
+pub(crate) struct AsyncPollPending;
+#[cfg(feature = "async")]
+pub(crate) static WAKER_REGISTRY_KEY: u8 = 0;
 
 impl Drop for Lua {
     fn drop(&mut self) {
@@ -59,7 +72,10 @@ impl Drop for Lua {
                         && extra.ref_stack_max as usize == extra.ref_free.len(),
                     "reference leak detected"
                 );
-                *mlua_expect!(extra.registry_unref_list.lock(), "unref list poisoned") = None;
+                *mlua_expect!(
+                    extra.registry_unref_list.try_borrow_mut(),
+                    "unref list borrowed"
+                ) = None;
                 ffi::lua_close(self.state);
             }
         }
@@ -113,55 +129,25 @@ impl Lua {
 
     /// Constructs a new Lua instance from the existing state.
     pub unsafe fn init_from_ptr(state: *mut ffi::lua_State) -> Lua {
-        #[cfg(any(feature = "lua53", feature = "lua52"))]
         let main_state = get_main_state(state);
-        #[cfg(any(feature = "lua51", feature = "luajit"))]
-        let main_state = {
-            set_main_state(state);
-            state
-        };
         let main_state_top = ffi::lua_gettop(state);
 
         let ref_thread = mlua_expect!(
             protect_lua_closure(main_state, 0, 0, |state| {
                 init_error_registry(state);
 
-                // Create the function metatables and place them in the registry
+                // Create the internal metatables and place them in the registry
                 // to prevent them from being garbage collected.
 
-                ffi::lua_pushlightuserdata(
-                    state,
-                    &FUNCTION_CALLBACK_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
-                );
-
-                ffi::lua_newtable(state);
-
-                ffi::lua_pushstring(state, cstr!("__gc"));
-                ffi::lua_pushcfunction(state, userdata_destructor::<Callback>);
-                ffi::lua_rawset(state, -3);
-
-                ffi::lua_pushstring(state, cstr!("__metatable"));
-                ffi::lua_pushboolean(state, 0);
-                ffi::lua_rawset(state, -3);
-
-                ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
-
-                ffi::lua_pushlightuserdata(
-                    state,
-                    &FUNCTION_EXTRA_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
-                );
-
-                ffi::lua_newtable(state);
-
-                ffi::lua_pushstring(state, cstr!("__gc"));
-                ffi::lua_pushcfunction(state, userdata_destructor::<Arc<RefCell<ExtraData>>>);
-                ffi::lua_rawset(state, -3);
-
-                ffi::lua_pushstring(state, cstr!("__metatable"));
-                ffi::lua_pushboolean(state, 0);
-                ffi::lua_rawset(state, -3);
-
-                ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
+                init_gc_metatable_for::<Callback>(state, None);
+                init_gc_metatable_for::<Lua>(state, None);
+                #[cfg(feature = "async")]
+                {
+                    init_gc_metatable_for::<AsyncCallback>(state, None);
+                    init_gc_metatable_for::<LocalBoxFuture<Result<MultiValue>>>(state, None);
+                    init_gc_metatable_for::<AsyncPollPending>(state, None);
+                    init_gc_metatable_for::<Waker>(state, None);
+                }
 
                 // Create ref stack thread and place it in the registry to prevent it from being garbage
                 // collected.
@@ -175,9 +161,9 @@ impl Lua {
 
         // Create ExtraData
 
-        let extra = Arc::new(RefCell::new(ExtraData {
+        let extra = Rc::new(RefCell::new(ExtraData {
             registered_userdata: HashMap::new(),
-            registry_unref_list: Arc::new(Mutex::new(Some(Vec::new()))),
+            registry_unref_list: Rc::new(RefCell::new(Some(Vec::new()))),
             ref_thread,
             // We need 1 extra stack space to move values in and out of the ref stack.
             ref_stack_size: ffi::LUA_MINSTACK - 1,
@@ -206,7 +192,7 @@ impl Lua {
     pub fn entrypoint1<'lua, 'callback, R, F>(&'lua self, func: F) -> Result<c_int>
     where
         R: ToLua<'callback>,
-        F: 'static + Send + Fn(&'callback Lua) -> Result<R>,
+        F: 'static + Fn(&'callback Lua) -> Result<R>,
     {
         let cb = self.create_callback(Box::new(move |lua, _| func(lua)?.to_lua_multi(lua)))?;
         unsafe { self.push_value(cb.call(())?).map(|_| 1) }
@@ -463,7 +449,7 @@ impl Lua {
     where
         A: FromLuaMulti<'callback>,
         R: ToLuaMulti<'callback>,
-        F: 'static + Send + Fn(&'callback Lua, A) -> Result<R>,
+        F: 'static + Fn(&'callback Lua, A) -> Result<R>,
     {
         self.create_callback(Box::new(move |lua, args| {
             func(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
@@ -483,7 +469,7 @@ impl Lua {
     where
         A: FromLuaMulti<'callback>,
         R: ToLuaMulti<'callback>,
-        F: 'static + Send + FnMut(&'callback Lua, A) -> Result<R>,
+        F: 'static + FnMut(&'callback Lua, A) -> Result<R>,
     {
         let func = RefCell::new(func);
         self.create_function(move |lua, args| {
@@ -493,6 +479,68 @@ impl Lua {
         })
     }
 
+    /// Wraps a Rust async function or closure, creating a callable Lua function handle to it.
+    ///
+    /// While executing the function Rust will poll Future and if the result is not ready, call
+    /// `lua_yield()` returning internal representation of a `Poll::Pending` value.
+    ///
+    /// The function must be called inside [`Thread`] coroutine to be able to suspend its execution.
+    /// An executor could be used together with [`ThreadStream`] and mlua will use a provided Waker
+    /// in that case. Otherwise noop waker will be used if try to call the function outside of Rust
+    /// executors.
+    ///
+    /// # Examples
+    ///
+    /// Non blocking sleep:
+    ///
+    /// ```
+    /// use std::time::Duration;
+    /// use futures_executor::block_on;
+    /// use futures_timer::Delay;
+    /// # use mlua::{Lua, Result, Thread};
+    ///
+    /// async fn sleep(_lua: &Lua, n: u64) -> Result<&'static str> {
+    ///     Delay::new(Duration::from_secs(n)).await;
+    ///     Ok("done")
+    /// }
+    ///
+    /// # fn main() -> Result<()> {
+    /// # let lua = Lua::new();
+    /// lua.globals().set("async_sleep", lua.create_async_function(sleep)?)?;
+    /// let thr = lua.load("coroutine.create(function(n) return async_sleep(n) end)").eval::<Thread>()?;
+    /// let res: String = block_on(async {
+    ///     thr.into_async(1).await // Sleep 1 second
+    /// })?;
+    ///
+    /// assert_eq!(res, "done");
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`Thread`]: struct.Thread.html
+    /// [`ThreadStream`]: struct.ThreadStream.html
+    #[cfg(feature = "async")]
+    pub fn create_async_function<'lua, 'callback, A, R, F, FR>(
+        &'lua self,
+        func: F,
+    ) -> Result<Function<'lua>>
+    where
+        A: FromLuaMulti<'callback>,
+        R: ToLuaMulti<'callback>,
+        F: 'static + Fn(&'callback Lua, A) -> FR,
+        FR: 'static + Future<Output = Result<R>>,
+    {
+        self.create_async_callback(Box::new(move |lua, args| {
+            let args = match A::from_lua_multi(args, lua) {
+                Ok(x) => x,
+                Err(e) => return future::err(e).boxed_local(),
+            };
+            func(lua, args)
+                .and_then(move |x| future::ready(x.to_lua_multi(lua)))
+                .boxed_local()
+        }))
+    }
+
     /// Wraps a Lua function into a new thread (or coroutine).
     ///
     /// Equivalent to `coroutine.create`.
@@ -513,7 +561,7 @@ impl Lua {
     /// Create a Lua userdata object from a custom userdata type.
     pub fn create_userdata<T>(&self, data: T) -> Result<AnyUserData>
     where
-        T: 'static + Send + UserData,
+        T: 'static + UserData,
     {
         unsafe { self.make_userdata(data) }
     }
@@ -540,33 +588,6 @@ impl Lua {
         }
     }
 
-    /// Calls the given function with a `Scope` parameter, giving the function the ability to create
-    /// userdata and callbacks from rust types that are !Send or non-'static.
-    ///
-    /// The lifetime of any function or userdata created through `Scope` lasts only until the
-    /// completion of this method call, on completion all such created values are automatically
-    /// dropped and Lua references to them are invalidated.  If a script accesses a value created
-    /// through `Scope` outside of this method, a Lua error will result.  Since we can ensure the
-    /// lifetime of values created through `Scope`, and we know that `Lua` cannot be sent to another
-    /// thread while `Scope` is live, it is safe to allow !Send datatypes and whose lifetimes only
-    /// outlive the scope lifetime.
-    ///
-    /// Inside the scope callback, all handles created through Scope will share the same unique 'lua
-    /// lifetime of the parent `Lua`.  This allows scoped and non-scoped values to be mixed in
-    /// API calls, which is very useful (e.g. passing a scoped userdata to a non-scoped function).
-    /// However, this also enables handles to scoped values to be trivially leaked from the given
-    /// callback. This is not dangerous, though!  After the callback returns, all scoped values are
-    /// invalidated, which means that though references may exist, the Rust types backing them have
-    /// dropped.  `Function` types will error when called, and `AnyUserData` will be typeless.  It
-    /// would be impossible to prevent handles to scoped values from escaping anyway, since you
-    /// would always be able to smuggle them through Lua state.
-    pub fn scope<'scope, 'lua: 'scope, F, R>(&'lua self, f: F) -> R
-    where
-        F: FnOnce(&Scope<'lua, 'scope>) -> R,
-    {
-        f(&Scope::new(self))
-    }
-
     /// Attempts to coerce a Lua value into a String in a manner consistent with Lua's internal
     /// behavior.
     ///
@@ -806,7 +827,7 @@ impl Lua {
     /// `Error::MismatchedRegistryKey` if passed a `RegistryKey` that was not created with a
     /// matching `Lua` state.
     pub fn owns_registry_value(&self, key: &RegistryKey) -> bool {
-        Arc::ptr_eq(&key.unref_list, &self.extra.borrow().registry_unref_list)
+        Rc::ptr_eq(&key.unref_list, &self.extra.borrow().registry_unref_list)
     }
 
     /// Remove any registry values whose `RegistryKey`s have all been dropped.
@@ -818,8 +839,8 @@ impl Lua {
         unsafe {
             let unref_list = mem::replace(
                 &mut *mlua_expect!(
-                    self.extra.borrow().registry_unref_list.lock(),
-                    "unref list poisoned"
+                    self.extra.borrow().registry_unref_list.try_borrow_mut(),
+                    "unref list borrowed"
                 ),
                 Some(Vec::new()),
             );
@@ -1009,7 +1030,12 @@ impl Lua {
             })?;
         }
 
-        if methods.methods.is_empty() {
+        #[cfg(feature = "async")]
+        let no_methods = methods.methods.is_empty() && methods.async_methods.is_empty();
+        #[cfg(not(feature = "async"))]
+        let no_methods = methods.methods.is_empty();
+
+        if no_methods {
             init_userdata_metatable::<RefCell<T>>(self.state, -1, None)?;
         } else {
             protect_lua_closure(self.state, 0, 1, |state| {
@@ -1022,6 +1048,14 @@ impl Lua {
                     ffi::lua_rawset(state, -3);
                 })?;
             }
+            #[cfg(feature = "async")]
+            for (k, m) in methods.async_methods {
+                push_string(self.state, &k)?;
+                self.push_value(Value::Function(self.create_async_callback(m)?))?;
+                protect_lua_closure(self.state, 3, 1, |state| {
+                    ffi::lua_rawset(state, -3);
+                })?;
+            }
 
             init_userdata_metatable::<RefCell<T>>(self.state, -2, Some(-1))?;
             ffi::lua_pop(self.state, 1);
@@ -1053,10 +1087,10 @@ impl Lua {
     ) -> Result<Function<'lua>> {
         unsafe extern "C" fn call_callback(state: *mut ffi::lua_State) -> c_int {
             callback_error(state, |nargs| {
-                if ffi::lua_type(state, ffi::lua_upvalueindex(1)) == ffi::LUA_TNIL {
-                    return Err(Error::CallbackDestructed);
-                }
-                if ffi::lua_type(state, ffi::lua_upvalueindex(2)) == ffi::LUA_TNIL {
+                let func =
+                    get_meta_gc_userdata::<Callback, Callback>(state, ffi::lua_upvalueindex(1));
+                let lua = get_gc_userdata::<Lua>(state, ffi::lua_upvalueindex(2));
+                if func.is_null() || lua.is_null() {
                     return Err(Error::CallbackDestructed);
                 }
 
@@ -1064,16 +1098,8 @@ impl Lua {
                     check_stack(state, ffi::LUA_MINSTACK - nargs)?;
                 }
 
-                let extra =
-                    get_userdata::<Arc<RefCell<ExtraData>>>(state, ffi::lua_upvalueindex(2));
-
-                let lua = Lua {
-                    state: state,
-                    main_state: get_main_state(state),
-                    extra: (*extra).clone(),
-                    ephemeral: true,
-                    _no_ref_unwind_safe: PhantomData,
-                };
+                let lua = &mut *lua;
+                lua.state = state;
 
                 let mut args = MultiValue::new();
                 args.reserve(nargs as usize);
@@ -1081,9 +1107,7 @@ impl Lua {
                     args.push_front(lua.pop_value());
                 }
 
-                let func = get_userdata::<Callback>(state, ffi::lua_upvalueindex(1));
-
-                let results = (*func)(&lua, args)?;
+                let results = (*func)(lua, args)?;
                 let nresults = results.len() as c_int;
 
                 check_stack(state, nresults)?;
@@ -1099,21 +1123,8 @@ impl Lua {
             let _sg = StackGuard::new(self.state);
             assert_stack(self.state, 6);
 
-            push_userdata::<Callback>(self.state, func)?;
-            ffi::lua_pushlightuserdata(
-                self.state,
-                &FUNCTION_CALLBACK_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
-            );
-            ffi::lua_rawget(self.state, ffi::LUA_REGISTRYINDEX);
-            ffi::lua_setmetatable(self.state, -2);
-
-            push_userdata::<Arc<RefCell<ExtraData>>>(self.state, self.extra.clone())?;
-            ffi::lua_pushlightuserdata(
-                self.state,
-                &FUNCTION_EXTRA_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
-            );
-            ffi::lua_rawget(self.state, ffi::LUA_REGISTRYINDEX);
-            ffi::lua_setmetatable(self.state, -2);
+            push_meta_gc_userdata::<Callback, _>(self.state, func)?;
+            push_gc_userdata(self.state, self.clone())?;
 
             protect_lua_closure(self.state, 2, 1, |state| {
                 ffi::lua_pushcclosure(state, call_callback, 2);
@@ -1123,7 +1134,140 @@ impl Lua {
         }
     }
 
-    // Does not require Send bounds, which can lead to unsafety.
+    #[cfg(feature = "async")]
+    pub(crate) fn create_async_callback<'lua, 'callback>(
+        &'lua self,
+        func: AsyncCallback<'callback, 'static>,
+    ) -> Result<Function<'lua>> {
+        #[cfg(any(feature = "lua53", feature = "lua52"))]
+        self.load_from_std_lib(StdLib::COROUTINE)?;
+
+        unsafe extern "C" fn call_callback(state: *mut ffi::lua_State) -> c_int {
+            callback_error(state, |nargs| {
+                let func = get_meta_gc_userdata::<AsyncCallback, AsyncCallback>(
+                    state,
+                    ffi::lua_upvalueindex(1),
+                );
+                let lua = get_gc_userdata::<Lua>(state, ffi::lua_upvalueindex(2));
+                if func.is_null() || lua.is_null() {
+                    return Err(Error::CallbackDestructed);
+                }
+
+                if nargs < ffi::LUA_MINSTACK {
+                    check_stack(state, ffi::LUA_MINSTACK - nargs)?;
+                }
+
+                let lua = &mut *lua;
+                lua.state = state;
+
+                let mut args = MultiValue::new();
+                args.reserve(nargs as usize);
+                for _ in 0..nargs {
+                    args.push_front(lua.pop_value());
+                }
+
+                let fut = (*func)(lua, args);
+                push_gc_userdata(state, fut)?;
+                push_gc_userdata(state, lua.clone())?;
+
+                ffi::lua_pushcclosure(state, poll_future, 2);
+
+                Ok(1)
+            })
+        }
+
+        unsafe extern "C" fn poll_future(state: *mut ffi::lua_State) -> c_int {
+            callback_error(state, |nargs| {
+                let fut = get_gc_userdata::<LocalBoxFuture<Result<MultiValue>>>(
+                    state,
+                    ffi::lua_upvalueindex(1),
+                );
+                let lua = get_gc_userdata::<Lua>(state, ffi::lua_upvalueindex(2));
+                if fut.is_null() || lua.is_null() {
+                    return Err(Error::CallbackDestructed);
+                }
+
+                if nargs < ffi::LUA_MINSTACK {
+                    check_stack(state, ffi::LUA_MINSTACK - nargs)?;
+                }
+
+                let lua = &mut *lua;
+                let mut waker = noop_waker();
+
+                // Try to get an outer poll waker
+                ffi::lua_pushlightuserdata(
+                    state,
+                    &WAKER_REGISTRY_KEY as *const u8 as *mut ::std::os::raw::c_void,
+                );
+                ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
+                if let Some(w) = get_gc_userdata::<Waker>(state, -1).as_ref() {
+                    waker = (*w).clone();
+                }
+                ffi::lua_pop(state, 1);
+
+                let mut ctx = Context::from_waker(&waker);
+
+                match (*fut).as_mut().poll(&mut ctx) {
+                    Poll::Pending => {
+                        check_stack(state, 6)?;
+                        ffi::lua_pushboolean(state, 0);
+                        push_gc_userdata(state, AsyncPollPending)?;
+                        Ok(2)
+                    }
+                    Poll::Ready(results) => {
+                        let results = lua.create_sequence_from(results?)?;
+                        check_stack(state, 2)?;
+                        ffi::lua_pushboolean(state, 1);
+                        lua.push_value(Value::Table(results))?;
+                        Ok(2)
+                    }
+                }
+            })
+        }
+
+        let get_poll = unsafe {
+            let _sg = StackGuard::new(self.state);
+            assert_stack(self.state, 6);
+
+            push_meta_gc_userdata::<AsyncCallback, _>(self.state, func)?;
+            push_gc_userdata(self.state, self.clone())?;
+
+            protect_lua_closure(self.state, 2, 1, |state| {
+                ffi::lua_pushcclosure(state, call_callback, 2);
+            })?;
+
+            Function(self.pop_ref())
+        };
+
+        let env = self.create_table()?;
+        env.set("get_poll", get_poll)?;
+        env.set("coroutine", self.globals().get::<_, Value>("coroutine")?)?;
+        env.set(
+            "unpack",
+            self.create_function(|_, tbl: Table| {
+                Ok(MultiValue::from_vec(
+                    tbl.sequence_values().collect::<Result<Vec<Value>>>()?,
+                ))
+            })?,
+        )?;
+
+        self.load(
+            r#"
+            local poll = get_poll(...)
+            while true do
+                ready, res = poll()
+                if ready then
+                    return unpack(res)
+                end
+                coroutine.yield(res)
+            end
+            "#,
+        )
+        .set_name("_mlua_async_poll")?
+        .set_environment(env)?
+        .into_function()
+    }
+
     pub(crate) unsafe fn make_userdata<T>(&self, data: T) -> Result<AnyUserData>
     where
         T: 'static + UserData,
@@ -1143,6 +1287,16 @@ impl Lua {
 
         Ok(AnyUserData(self.pop_ref()))
     }
+
+    pub(crate) fn clone(&self) -> Self {
+        Lua {
+            state: self.state,
+            main_state: self.main_state,
+            extra: self.extra.clone(),
+            ephemeral: true,
+            _no_ref_unwind_safe: PhantomData,
+        }
+    }
 }
 
 /// Returned from [`Lua::load`] and is used to finalize loading and executing Lua main chunks.
@@ -1343,11 +1497,10 @@ unsafe fn ref_stack_pop(extra: &mut ExtraData) -> c_int {
     }
 }
 
-static FUNCTION_CALLBACK_METATABLE_REGISTRY_KEY: u8 = 0;
-static FUNCTION_EXTRA_METATABLE_REGISTRY_KEY: u8 = 0;
-
 struct StaticUserDataMethods<'lua, T: 'static + UserData> {
     methods: Vec<(Vec<u8>, Callback<'lua, 'static>)>,
+    #[cfg(feature = "async")]
+    async_methods: Vec<(Vec<u8>, AsyncCallback<'lua, 'static>)>,
     meta_methods: Vec<(MetaMethod, Callback<'lua, 'static>)>,
     _type: PhantomData<T>,
 }
@@ -1356,6 +1509,8 @@ impl<'lua, T: 'static + UserData> Default for StaticUserDataMethods<'lua, T> {
     fn default() -> StaticUserDataMethods<'lua, T> {
         StaticUserDataMethods {
             methods: Vec::new(),
+            #[cfg(feature = "async")]
+            async_methods: Vec::new(),
             meta_methods: Vec::new(),
             _type: PhantomData,
         }
@@ -1368,7 +1523,7 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + Fn(&'lua Lua, &T, A) -> Result<R>,
+        M: 'static + Fn(&'lua Lua, &T, A) -> Result<R>,
     {
         self.methods
             .push((name.as_ref().to_vec(), Self::box_method(method)));
@@ -1379,18 +1534,32 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
+        M: 'static + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
     {
         self.methods
             .push((name.as_ref().to_vec(), Self::box_method_mut(method)));
     }
 
+    #[cfg(feature = "async")]
+    fn add_async_method<S, A, R, M, MR>(&mut self, name: &S, method: M)
+    where
+        T: Clone,
+        S: ?Sized + AsRef<[u8]>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        M: 'static + Fn(&'lua Lua, T, A) -> MR,
+        MR: 'static + Future<Output = Result<R>>,
+    {
+        self.async_methods
+            .push((name.as_ref().to_vec(), Self::box_async_method(method)));
+    }
+
     fn add_function<S, A, R, F>(&mut self, name: &S, function: F)
     where
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + Fn(&'lua Lua, A) -> Result<R>,
+        F: 'static + Fn(&'lua Lua, A) -> Result<R>,
     {
         self.methods
             .push((name.as_ref().to_vec(), Self::box_function(function)));
@@ -1401,17 +1570,31 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + FnMut(&'lua Lua, A) -> Result<R>,
+        F: 'static + FnMut(&'lua Lua, A) -> Result<R>,
     {
         self.methods
             .push((name.as_ref().to_vec(), Self::box_function_mut(function)));
     }
 
+    #[cfg(feature = "async")]
+    fn add_async_function<S, A, R, F, FR>(&mut self, name: &S, function: F)
+    where
+        T: Clone,
+        S: ?Sized + AsRef<[u8]>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        F: 'static + Fn(&'lua Lua, A) -> FR,
+        FR: 'static + Future<Output = Result<R>>,
+    {
+        self.async_methods
+            .push((name.as_ref().to_vec(), Self::box_async_function(function)));
+    }
+
     fn add_meta_method<A, R, M>(&mut self, meta: MetaMethod, method: M)
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + Fn(&'lua Lua, &T, A) -> Result<R>,
+        M: 'static + Fn(&'lua Lua, &T, A) -> Result<R>,
     {
         self.meta_methods.push((meta, Self::box_method(method)));
     }
@@ -1420,7 +1603,7 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
+        M: 'static + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
     {
         self.meta_methods.push((meta, Self::box_method_mut(method)));
     }
@@ -1429,7 +1612,7 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + Fn(&'lua Lua, A) -> Result<R>,
+        F: 'static + Fn(&'lua Lua, A) -> Result<R>,
     {
         self.meta_methods.push((meta, Self::box_function(function)));
     }
@@ -1438,7 +1621,7 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + FnMut(&'lua Lua, A) -> Result<R>,
+        F: 'static + FnMut(&'lua Lua, A) -> Result<R>,
     {
         self.meta_methods
             .push((meta, Self::box_function_mut(function)));
@@ -1450,7 +1633,7 @@ impl<'lua, T: 'static + UserData> StaticUserDataMethods<'lua, T> {
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + Fn(&'lua Lua, &T, A) -> Result<R>,
+        M: 'static + Fn(&'lua Lua, &T, A) -> Result<R>,
     {
         Box::new(move |lua, mut args| {
             if let Some(front) = args.pop_front() {
@@ -1471,7 +1654,7 @@ impl<'lua, T: 'static + UserData> StaticUserDataMethods<'lua, T> {
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
+        M: 'static + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
     {
         let method = RefCell::new(method);
         Box::new(move |lua, mut args| {
@@ -1492,11 +1675,43 @@ impl<'lua, T: 'static + UserData> StaticUserDataMethods<'lua, T> {
         })
     }
 
+    #[cfg(feature = "async")]
+    fn box_async_method<A, R, M, MR>(method: M) -> AsyncCallback<'lua, 'static>
+    where
+        T: Clone,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        M: 'static + Fn(&'lua Lua, T, A) -> MR,
+        MR: 'static + Future<Output = Result<R>>,
+    {
+        Box::new(move |lua, mut args| {
+            let fut = || {
+                if let Some(front) = args.pop_front() {
+                    let userdata = AnyUserData::from_lua(front, lua)?;
+                    let userdata = userdata.borrow::<T>()?.clone();
+                    Ok(method(lua, userdata, A::from_lua_multi(args, lua)?))
+                } else {
+                    Err(Error::FromLuaConversionError {
+                        from: "missing argument",
+                        to: "userdata",
+                        message: None,
+                    })
+                }
+            };
+            match fut() {
+                Ok(f) => f
+                    .and_then(move |fr| future::ready(fr.to_lua_multi(lua)))
+                    .boxed_local(),
+                Err(e) => future::err(e).boxed_local(),
+            }
+        })
+    }
+
     fn box_function<A, R, F>(function: F) -> Callback<'lua, 'static>
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + Fn(&'lua Lua, A) -> Result<R>,
+        F: 'static + Fn(&'lua Lua, A) -> Result<R>,
     {
         Box::new(move |lua, args| function(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua))
     }
@@ -1505,7 +1720,7 @@ impl<'lua, T: 'static + UserData> StaticUserDataMethods<'lua, T> {
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + FnMut(&'lua Lua, A) -> Result<R>,
+        F: 'static + FnMut(&'lua Lua, A) -> Result<R>,
     {
         let function = RefCell::new(function);
         Box::new(move |lua, args| {
@@ -1515,4 +1730,23 @@ impl<'lua, T: 'static + UserData> StaticUserDataMethods<'lua, T> {
             function(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
         })
     }
+
+    #[cfg(feature = "async")]
+    fn box_async_function<A, R, F, FR>(function: F) -> AsyncCallback<'lua, 'static>
+    where
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        F: 'static + Fn(&'lua Lua, A) -> FR,
+        FR: 'static + Future<Output = Result<R>>,
+    {
+        Box::new(move |lua, args| {
+            let args = match A::from_lua_multi(args, lua) {
+                Ok(x) => x,
+                Err(e) => return future::err(e).boxed_local(),
+            };
+            function(lua, args)
+                .and_then(move |x| future::ready(x.to_lua_multi(lua)))
+                .boxed_local()
+        })
+    }
 }

src/multi.rs

@@ -146,7 +146,7 @@ macro_rules! impl_tuple {
         }
 
         impl<'lua> FromLuaMulti<'lua> for () {
-            fn from_lua_multi(_: MultiValue, _: &'lua Lua) -> Result<Self> {
+            fn from_lua_multi(_: MultiValue<'lua>, _: &'lua Lua) -> Result<Self> {
                 Ok(())
             }
         }

src/prelude.rs

@@ -5,8 +5,11 @@ pub use crate::{
     ExternalError as LuaExternalError, ExternalResult as LuaExternalResult, FromLua, FromLuaMulti,
     Function as LuaFunction, Integer as LuaInteger, LightUserData as LuaLightUserData, Lua,
     MetaMethod as LuaMetaMethod, MultiValue as LuaMultiValue, Nil as LuaNil, Number as LuaNumber,
-    RegistryKey as LuaRegistryKey, Result as LuaResult, Scope as LuaScope, String as LuaString,
-    Table as LuaTable, TablePairs as LuaTablePairs, TableSequence as LuaTableSequence,
-    Thread as LuaThread, ThreadStatus as LuaThreadStatus, ToLua, ToLuaMulti,
-    UserData as LuaUserData, UserDataMethods as LuaUserDataMethods, Value as LuaValue,
+    RegistryKey as LuaRegistryKey, Result as LuaResult, String as LuaString, Table as LuaTable,
+    TablePairs as LuaTablePairs, TableSequence as LuaTableSequence, Thread as LuaThread,
+    ThreadStatus as LuaThreadStatus, ToLua, ToLuaMulti, UserData as LuaUserData,
+    UserDataMethods as LuaUserDataMethods, Value as LuaValue,
 };
+
+#[cfg(feature = "async")]
+pub use crate::AsyncThread as LuaAsyncThread;

src/scope.rs

@@ -1,484 +0,0 @@
-use std::any::Any;
-use std::cell::Cell;
-use std::cell::RefCell;
-use std::marker::PhantomData;
-use std::mem;
-use std::os::raw::c_void;
-use std::rc::Rc;
-
-use crate::error::{Error, Result};
-use crate::ffi;
-use crate::function::Function;
-use crate::lua::Lua;
-use crate::types::{Callback, LuaRef};
-use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataMethods};
-use crate::util::{
-    assert_stack, init_userdata_metatable, protect_lua_closure, push_string, push_userdata,
-    take_userdata, StackGuard,
-};
-use crate::value::{FromLuaMulti, MultiValue, ToLuaMulti, Value};
-
-/// Constructed by the [`Lua::scope`] method, allows temporarily creating Lua userdata and
-/// callbacks that are not required to be Send or 'static.
-///
-/// See [`Lua::scope`] for more details.
-///
-/// [`Lua::scope`]: struct.Lua.html#method.scope
-pub struct Scope<'lua, 'scope> {
-    lua: &'lua Lua,
-    destructors: RefCell<Vec<(LuaRef<'lua>, fn(LuaRef<'lua>) -> Box<dyn Any>)>>,
-    _scope_invariant: PhantomData<Cell<&'scope ()>>,
-}
-
-impl<'lua, 'scope> Scope<'lua, 'scope> {
-    pub(crate) fn new(lua: &'lua Lua) -> Scope<'lua, 'scope> {
-        Scope {
-            lua,
-            destructors: RefCell::new(Vec::new()),
-            _scope_invariant: PhantomData,
-        }
-    }
-
-    /// Wraps a Rust function or closure, creating a callable Lua function handle to it.
-    ///
-    /// This is a version of [`Lua::create_function`] that creates a callback which expires on
-    /// scope drop.  See [`Lua::scope`] for more details.
-    ///
-    /// [`Lua::create_function`]: struct.Lua.html#method.create_function
-    /// [`Lua::scope`]: struct.Lua.html#method.scope
-    pub fn create_function<'callback, A, R, F>(&'callback self, func: F) -> Result<Function<'lua>>
-    where
-        A: FromLuaMulti<'callback>,
-        R: ToLuaMulti<'callback>,
-        F: 'scope + Fn(&'callback Lua, A) -> Result<R>,
-    {
-        // Safe, because 'scope must outlive 'callback (due to Self containing 'scope), however the
-        // callback itself must be 'scope lifetime, so the function should not be able to capture
-        // anything of 'callback lifetime.  'scope can't be shortened due to being invariant, and
-        // the 'callback lifetime here can't be enlarged due to coming from a universal
-        // quantification in Lua::scope.
-        //
-        // I hope I got this explanation right, but in any case this is tested with compiletest_rs
-        // to make sure callbacks can't capture handles with lifetime outside the scope, inside the
-        // scope, and owned inside the callback itself.
-        unsafe {
-            self.create_callback(Box::new(move |lua, args| {
-                func(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            }))
-        }
-    }
-
-    /// Wraps a Rust mutable closure, creating a callable Lua function handle to it.
-    ///
-    /// This is a version of [`Lua::create_function_mut`] that creates a callback which expires
-    /// on scope drop.  See [`Lua::scope`] and [`Scope::create_function`] for more details.
-    ///
-    /// [`Lua::create_function_mut`]: struct.Lua.html#method.create_function_mut
-    /// [`Lua::scope`]: struct.Lua.html#method.scope
-    /// [`Scope::create_function`]: #method.create_function
-    pub fn create_function_mut<'callback, A, R, F>(
-        &'callback self,
-        func: F,
-    ) -> Result<Function<'lua>>
-    where
-        A: FromLuaMulti<'callback>,
-        R: ToLuaMulti<'callback>,
-        F: 'scope + FnMut(&'callback Lua, A) -> Result<R>,
-    {
-        let func = RefCell::new(func);
-        self.create_function(move |lua, args| {
-            (&mut *func
-                .try_borrow_mut()
-                .map_err(|_| Error::RecursiveMutCallback)?)(lua, args)
-        })
-    }
-
-    /// Create a Lua userdata object from a custom userdata type.
-    ///
-    /// This is a version of [`Lua::create_userdata`] that creates a userdata which expires on
-    /// scope drop, and does not require that the userdata type be Send (but still requires that the
-    /// UserData be 'static).  See [`Lua::scope`] for more details.
-    ///
-    /// [`Lua::create_userdata`]: struct.Lua.html#method.create_userdata
-    /// [`Lua::scope`]: struct.Lua.html#method.scope
-    pub fn create_static_userdata<T>(&self, data: T) -> Result<AnyUserData<'lua>>
-    where
-        T: 'static + UserData,
-    {
-        // Safe even though T may not be Send, because the parent Lua cannot be sent to another
-        // thread while the Scope is alive (or the returned AnyUserData handle even).
-        unsafe {
-            let u = self.lua.make_userdata(data)?;
-            self.destructors.borrow_mut().push((u.0.clone(), |u| {
-                let state = u.lua.state;
-                assert_stack(state, 2);
-                u.lua.push_ref(&u);
-                // We know the destructor has not run yet because we hold a reference to the
-                // userdata.
-                Box::new(take_userdata::<RefCell<T>>(state))
-            }));
-            Ok(u)
-        }
-    }
-
-    /// Create a Lua userdata object from a custom userdata type.
-    ///
-    /// This is a version of [`Lua::create_userdata`] that creates a userdata which expires on
-    /// scope drop, and does not require that the userdata type be Send or 'static. See
-    /// [`Lua::scope`] for more details.
-    ///
-    /// Lifting the requirement that the UserData type be 'static comes with some important
-    /// limitations, so if you only need to eliminate the Send requirement, it is probably better to
-    /// use [`Scope::create_static_userdata`] instead.
-    ///
-    /// The main limitation that comes from using non-'static userdata is that the produced userdata
-    /// will no longer have a `TypeId` associated with it, becuase `TypeId` can only work for
-    /// 'static types.  This means that it is impossible, once the userdata is created, to get a
-    /// reference to it back *out* of an `AnyUserData` handle.  This also implies that the
-    /// "function" type methods that can be added via [`UserDataMethods`] (the ones that accept
-    /// `AnyUserData` as a first parameter) are vastly less useful.  Also, there is no way to re-use
-    /// a single metatable for multiple non-'static types, so there is a higher cost associated with
-    /// creating the userdata metatable each time a new userdata is created.
-    ///
-    /// [`create_static_userdata`]: #method.create_static_userdata
-    /// [`Lua::create_userdata`]: struct.Lua.html#method.create_userdata
-    /// [`Lua::scope`]: struct.Lua.html#method.scope
-    /// [`UserDataMethods`]: trait.UserDataMethods.html
-    pub fn create_nonstatic_userdata<T>(&self, data: T) -> Result<AnyUserData<'lua>>
-    where
-        T: 'scope + UserData,
-    {
-        let data = Rc::new(RefCell::new(data));
-
-        // 'callback outliving 'scope is a lie to make the types work out, required due to the
-        // inability to work with the more correct callback type that is universally quantified over
-        // 'lua.  This is safe though, because `UserData::add_methods` does not get to pick the 'lua
-        // lifetime, so none of the static methods UserData types can add can possibly capture
-        // parameters.
-        fn wrap_method<'scope, 'lua, 'callback: 'scope, T: 'scope>(
-            scope: &Scope<'lua, 'scope>,
-            data: Rc<RefCell<T>>,
-            method: NonStaticMethod<'callback, T>,
-        ) -> Result<Function<'lua>> {
-            // On methods that actually receive the userdata, we fake a type check on the passed in
-            // userdata, where we pretend there is a unique type per call to
-            // `Scope::create_nonstatic_userdata`.  You can grab a method from a userdata and call
-            // it on a mismatched userdata type, which when using normal 'static userdata will fail
-            // with a type mismatch, but here without this check would proceed as though you had
-            // called the method on the original value (since we otherwise completely ignore the
-            // first argument).
-            let check_data = data.clone();
-            let check_ud_type = move |lua: &'callback Lua, value| {
-                if let Some(value) = value {
-                    if let Value::UserData(u) = value {
-                        unsafe {
-                            assert_stack(lua.state, 1);
-                            lua.push_ref(&u.0);
-                            ffi::lua_getuservalue(lua.state, -1);
-                            #[cfg(any(feature = "lua52", feature = "lua51", feature = "luajit"))]
-                            {
-                                ffi::lua_pushinteger(lua.state, 1);
-                                ffi::lua_gettable(lua.state, -2);
-                                ffi::lua_remove(lua.state, -2);
-                            }
-                            return ffi::lua_touserdata(lua.state, -1)
-                                == check_data.as_ptr() as *mut c_void;
-                        }
-                    }
-                }
-
-                false
-            };
-
-            match method {
-                NonStaticMethod::Method(method) => {
-                    let method_data = data.clone();
-                    let f = Box::new(move |lua, mut args: MultiValue<'callback>| {
-                        if !check_ud_type(lua, args.pop_front()) {
-                            return Err(Error::UserDataTypeMismatch);
-                        }
-                        let data = method_data
-                            .try_borrow()
-                            .map_err(|_| Error::UserDataBorrowError)?;
-                        method(lua, &*data, args)
-                    });
-                    unsafe { scope.create_callback(f) }
-                }
-                NonStaticMethod::MethodMut(method) => {
-                    let method = RefCell::new(method);
-                    let method_data = data.clone();
-                    let f = Box::new(move |lua, mut args: MultiValue<'callback>| {
-                        if !check_ud_type(lua, args.pop_front()) {
-                            return Err(Error::UserDataTypeMismatch);
-                        }
-                        let mut method = method
-                            .try_borrow_mut()
-                            .map_err(|_| Error::RecursiveMutCallback)?;
-                        let mut data = method_data
-                            .try_borrow_mut()
-                            .map_err(|_| Error::UserDataBorrowMutError)?;
-                        (&mut *method)(lua, &mut *data, args)
-                    });
-                    unsafe { scope.create_callback(f) }
-                }
-                NonStaticMethod::Function(function) => unsafe { scope.create_callback(function) },
-                NonStaticMethod::FunctionMut(function) => {
-                    let function = RefCell::new(function);
-                    let f = Box::new(move |lua, args| {
-                        (&mut *function
-                            .try_borrow_mut()
-                            .map_err(|_| Error::RecursiveMutCallback)?)(
-                            lua, args
-                        )
-                    });
-                    unsafe { scope.create_callback(f) }
-                }
-            }
-        }
-
-        let mut ud_methods = NonStaticUserDataMethods::default();
-        T::add_methods(&mut ud_methods);
-
-        unsafe {
-            let lua = self.lua;
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 6);
-
-            push_userdata(lua.state, ())?;
-            #[cfg(feature = "lua53")]
-            ffi::lua_pushlightuserdata(lua.state, data.as_ptr() as *mut c_void);
-            #[cfg(any(feature = "lua52", feature = "lua51", feature = "luajit"))]
-            protect_lua_closure(lua.state, 0, 1, |state| {
-                // Lua 5.2/5.1 allows to store only table. Then we will wrap the value.
-                ffi::lua_createtable(state, 1, 0);
-                ffi::lua_pushinteger(state, 1);
-                ffi::lua_pushlightuserdata(state, data.as_ptr() as *mut c_void);
-                ffi::lua_settable(state, -3);
-            })?;
-            ffi::lua_setuservalue(lua.state, -2);
-
-            protect_lua_closure(lua.state, 0, 1, move |state| {
-                ffi::lua_newtable(state);
-            })?;
-
-            for (k, m) in ud_methods.meta_methods {
-                push_string(lua.state, k.name())?;
-                lua.push_value(Value::Function(wrap_method(self, data.clone(), m)?))?;
-
-                protect_lua_closure(lua.state, 3, 1, |state| {
-                    ffi::lua_rawset(state, -3);
-                })?;
-            }
-
-            if ud_methods.methods.is_empty() {
-                init_userdata_metatable::<()>(lua.state, -1, None)?;
-            } else {
-                protect_lua_closure(lua.state, 0, 1, |state| {
-                    ffi::lua_newtable(state);
-                })?;
-                for (k, m) in ud_methods.methods {
-                    push_string(lua.state, &k)?;
-                    lua.push_value(Value::Function(wrap_method(self, data.clone(), m)?))?;
-                    protect_lua_closure(lua.state, 3, 1, |state| {
-                        ffi::lua_rawset(state, -3);
-                    })?;
-                }
-
-                init_userdata_metatable::<()>(lua.state, -2, Some(-1))?;
-                ffi::lua_pop(lua.state, 1);
-            }
-
-            ffi::lua_setmetatable(lua.state, -2);
-
-            Ok(AnyUserData(lua.pop_ref()))
-        }
-    }
-
-    // Unsafe, because the callback can improperly capture any value with 'callback scope, such as
-    // improperly capturing an argument. Since the 'callback lifetime is chosen by the user and the
-    // lifetime of the callback itself is 'scope (non-'static), the borrow checker will happily pick
-    // a 'callback that outlives 'scope to allow this.  In order for this to be safe, the callback
-    // must NOT capture any parameters.
-    unsafe fn create_callback<'callback>(
-        &self,
-        f: Callback<'callback, 'scope>,
-    ) -> Result<Function<'lua>> {
-        let f = mem::transmute::<Callback<'callback, 'scope>, Callback<'lua, 'static>>(f);
-        let f = self.lua.create_callback(f)?;
-
-        let mut destructors = self.destructors.borrow_mut();
-        destructors.push((f.0.clone(), |f| {
-            let state = f.lua.state;
-            assert_stack(state, 3);
-            f.lua.push_ref(&f);
-
-            ffi::lua_getupvalue(state, -1, 1);
-            // We know the destructor has not run yet because we hold a reference to the callback.
-            let ud = take_userdata::<Callback>(state);
-
-            ffi::lua_pushnil(state);
-            ffi::lua_setupvalue(state, -2, 1);
-
-            ffi::lua_pop(state, 1);
-            Box::new(ud)
-        }));
-        Ok(f)
-    }
-}
-
-impl<'lua, 'scope> Drop for Scope<'lua, 'scope> {
-    fn drop(&mut self) {
-        // We separate the action of invalidating the userdata in Lua and actually dropping the
-        // userdata type into two phases.  This is so that, in the event a userdata drop panics, we
-        // can be sure that all of the userdata in Lua is actually invalidated.
-
-        // All destructors are non-panicking, so this is fine
-        let to_drop = self
-            .destructors
-            .get_mut()
-            .drain(..)
-            .map(|(r, dest)| dest(r))
-            .collect::<Vec<_>>();
-
-        drop(to_drop);
-    }
-}
-
-enum NonStaticMethod<'lua, T> {
-    Method(Box<dyn Fn(&'lua Lua, &T, MultiValue<'lua>) -> Result<MultiValue<'lua>>>),
-    MethodMut(Box<dyn FnMut(&'lua Lua, &mut T, MultiValue<'lua>) -> Result<MultiValue<'lua>>>),
-    Function(Box<dyn Fn(&'lua Lua, MultiValue<'lua>) -> Result<MultiValue<'lua>>>),
-    FunctionMut(Box<dyn FnMut(&'lua Lua, MultiValue<'lua>) -> Result<MultiValue<'lua>>>),
-}
-
-struct NonStaticUserDataMethods<'lua, T: UserData> {
-    methods: Vec<(Vec<u8>, NonStaticMethod<'lua, T>)>,
-    meta_methods: Vec<(MetaMethod, NonStaticMethod<'lua, T>)>,
-}
-
-impl<'lua, T: UserData> Default for NonStaticUserDataMethods<'lua, T> {
-    fn default() -> NonStaticUserDataMethods<'lua, T> {
-        NonStaticUserDataMethods {
-            methods: Vec::new(),
-            meta_methods: Vec::new(),
-        }
-    }
-}
-
-impl<'lua, T: UserData> UserDataMethods<'lua, T> for NonStaticUserDataMethods<'lua, T> {
-    fn add_method<S, A, R, M>(&mut self, name: &S, method: M)
-    where
-        S: ?Sized + AsRef<[u8]>,
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        M: 'static + Send + Fn(&'lua Lua, &T, A) -> Result<R>,
-    {
-        self.methods.push((
-            name.as_ref().to_vec(),
-            NonStaticMethod::Method(Box::new(move |lua, ud, args| {
-                method(lua, ud, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-
-    fn add_method_mut<S, A, R, M>(&mut self, name: &S, mut method: M)
-    where
-        S: ?Sized + AsRef<[u8]>,
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        M: 'static + Send + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
-    {
-        self.methods.push((
-            name.as_ref().to_vec(),
-            NonStaticMethod::MethodMut(Box::new(move |lua, ud, args| {
-                method(lua, ud, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-
-    fn add_function<S, A, R, F>(&mut self, name: &S, function: F)
-    where
-        S: ?Sized + AsRef<[u8]>,
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        F: 'static + Send + Fn(&'lua Lua, A) -> Result<R>,
-    {
-        self.methods.push((
-            name.as_ref().to_vec(),
-            NonStaticMethod::Function(Box::new(move |lua, args| {
-                function(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-
-    fn add_function_mut<S, A, R, F>(&mut self, name: &S, mut function: F)
-    where
-        S: ?Sized + AsRef<[u8]>,
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        F: 'static + Send + FnMut(&'lua Lua, A) -> Result<R>,
-    {
-        self.methods.push((
-            name.as_ref().to_vec(),
-            NonStaticMethod::FunctionMut(Box::new(move |lua, args| {
-                function(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-
-    fn add_meta_method<A, R, M>(&mut self, meta: MetaMethod, method: M)
-    where
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        M: 'static + Send + Fn(&'lua Lua, &T, A) -> Result<R>,
-    {
-        self.meta_methods.push((
-            meta,
-            NonStaticMethod::Method(Box::new(move |lua, ud, args| {
-                method(lua, ud, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-
-    fn add_meta_method_mut<A, R, M>(&mut self, meta: MetaMethod, mut method: M)
-    where
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        M: 'static + Send + FnMut(&'lua Lua, &mut T, A) -> Result<R>,
-    {
-        self.meta_methods.push((
-            meta,
-            NonStaticMethod::MethodMut(Box::new(move |lua, ud, args| {
-                method(lua, ud, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-
-    fn add_meta_function<A, R, F>(&mut self, meta: MetaMethod, function: F)
-    where
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        F: 'static + Send + Fn(&'lua Lua, A) -> Result<R>,
-    {
-        self.meta_methods.push((
-            meta,
-            NonStaticMethod::Function(Box::new(move |lua, args| {
-                function(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-
-    fn add_meta_function_mut<A, R, F>(&mut self, meta: MetaMethod, mut function: F)
-    where
-        A: FromLuaMulti<'lua>,
-        R: ToLuaMulti<'lua>,
-        F: 'static + Send + FnMut(&'lua Lua, A) -> Result<R>,
-    {
-        self.meta_methods.push((
-            meta,
-            NonStaticMethod::FunctionMut(Box::new(move |lua, args| {
-                function(lua, A::from_lua_multi(args, lua)?)?.to_lua_multi(lua)
-            })),
-        ));
-    }
-}

src/thread.rs

@@ -8,6 +8,24 @@ use crate::util::{
 };
 use crate::value::{FromLuaMulti, MultiValue, ToLuaMulti};
 
+#[cfg(feature = "async")]
+use {
+    crate::{
+        error::ExternalError,
+        lua::{AsyncPollPending, Lua, WAKER_REGISTRY_KEY},
+        util::{get_gc_userdata, push_gc_userdata},
+        value::Value,
+    },
+    futures_core::{future::Future, stream::Stream},
+    std::{
+        cell::RefCell,
+        marker::PhantomData,
+        os::raw::c_void,
+        pin::Pin,
+        task::{Context, Poll, Waker},
+    },
+};
+
 /// Status of a Lua thread (or coroutine).
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub enum ThreadStatus {
@@ -27,6 +45,15 @@ pub enum ThreadStatus {
 #[derive(Clone, Debug)]
 pub struct Thread<'lua>(pub(crate) LuaRef<'lua>);
 
+/// Thread (coroutine) representation as an async Future or Stream.
+#[cfg(feature = "async")]
+#[derive(Debug)]
+pub struct AsyncThread<'lua, R> {
+    thread: Thread<'lua>,
+    args0: RefCell<Option<Result<MultiValue<'lua>>>>,
+    ret: PhantomData<R>,
+}
+
 impl<'lua> Thread<'lua> {
     /// Resumes execution of this thread.
     ///
@@ -142,6 +169,62 @@ impl<'lua> Thread<'lua> {
             }
         }
     }
+
+    /// Converts Thread to an AsyncThread which implements Future and Stream traits.
+    ///
+    /// `args` are passed as arguments to the thread function for first call.
+    /// The object call `resume()` while polling and also allows to run rust futures
+    /// to completion using an executor.
+    ///
+    /// Using AsyncThread as a Stream allows to iterate through `coroutine.yield()`
+    /// values whereas Future version discards that values and poll until the final
+    /// one (returned from the thread function).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use mlua::{Error, Lua, Result, Thread};
+    /// use futures_executor::block_on;
+    /// use futures_util::stream::TryStreamExt;
+    /// # fn main() -> Result<()> {
+    /// # let lua = Lua::new();
+    /// let thread: Thread = lua.load(r#"
+    ///     coroutine.create(function(sum)
+    ///         for i = 1,10 do
+    ///             sum = sum + i
+    ///             coroutine.yield(sum)
+    ///         end
+    ///         return sum
+    ///     end)
+    /// "#).eval()?;
+    ///
+    /// let result = block_on(async {
+    ///     let mut s = thread.into_async::<_, i64>(1);
+    ///     let mut sum = 0;
+    ///     while let Some(n) = s.try_next().await? {
+    ///         sum += n;
+    ///     }
+    ///     Ok::<_, Error>(sum)
+    /// })?;
+    ///
+    /// assert_eq!(result, 286);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    #[cfg(feature = "async")]
+    pub fn into_async<A, R>(self, args: A) -> AsyncThread<'lua, R>
+    where
+        A: ToLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>,
+    {
+        let args = args.to_lua_multi(&self.0.lua);
+        AsyncThread {
+            thread: self,
+            args0: RefCell::new(Some(args)),
+            ret: PhantomData,
+        }
+    }
 }
 
 impl<'lua> PartialEq for Thread<'lua> {
@@ -149,3 +232,128 @@ impl<'lua> PartialEq for Thread<'lua> {
         self.0 == other.0
     }
 }
+
+#[cfg(feature = "async")]
+impl<'lua, R> Stream for AsyncThread<'lua, R>
+where
+    R: FromLuaMulti<'lua>,
+{
+    type Item = Result<R>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let lua = self.thread.0.lua;
+
+        match self.thread.status() {
+            ThreadStatus::Resumable => {}
+            _ => return Poll::Ready(None),
+        };
+
+        let _wg = WakerGuard::new(lua.state, cx.waker().clone());
+        let ret: MultiValue = if let Some(args) = self.args0.borrow_mut().take() {
+            self.thread.resume(args?)?
+        } else {
+            self.thread.resume(())?
+        };
+
+        if is_poll_pending(lua, &ret) {
+            return Poll::Pending;
+        }
+
+        cx.waker().wake_by_ref();
+        Poll::Ready(Some(R::from_lua_multi(ret, lua)))
+    }
+}
+
+#[cfg(feature = "async")]
+impl<'lua, R> Future for AsyncThread<'lua, R>
+where
+    R: FromLuaMulti<'lua>,
+{
+    type Output = Result<R>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let lua = self.thread.0.lua;
+
+        match self.thread.status() {
+            ThreadStatus::Resumable => {}
+            _ => return Poll::Ready(Err("Thread already finished".to_lua_err())),
+        };
+
+        let _wg = WakerGuard::new(lua.state, cx.waker().clone());
+        let ret: MultiValue = if let Some(args) = self.args0.borrow_mut().take() {
+            self.thread.resume(args?)?
+        } else {
+            self.thread.resume(())?
+        };
+
+        if is_poll_pending(lua, &ret) {
+            return Poll::Pending;
+        }
+
+        if let ThreadStatus::Resumable = self.thread.status() {
+            // Ignore value returned via yield()
+            cx.waker().wake_by_ref();
+            return Poll::Pending;
+        }
+
+        Poll::Ready(R::from_lua_multi(ret, lua))
+    }
+}
+
+#[cfg(feature = "async")]
+fn is_poll_pending(lua: &Lua, val: &MultiValue) -> bool {
+    if val.len() != 1 {
+        return false;
+    }
+
+    if let Some(Value::UserData(ud)) = val.iter().next() {
+        unsafe {
+            let _sg = StackGuard::new(lua.state);
+            assert_stack(lua.state, 3);
+
+            lua.push_ref(&ud.0);
+            let is_pending = get_gc_userdata::<AsyncPollPending>(lua.state, -1)
+                .as_ref()
+                .is_some();
+            ffi::lua_pop(lua.state, 1);
+
+            return is_pending;
+        }
+    }
+
+    false
+}
+
+#[cfg(feature = "async")]
+struct WakerGuard(*mut ffi::lua_State);
+
+#[cfg(feature = "async")]
+impl WakerGuard {
+    pub fn new(state: *mut ffi::lua_State, waker: Waker) -> Result<WakerGuard> {
+        unsafe {
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 6);
+
+            ffi::lua_pushlightuserdata(state, &WAKER_REGISTRY_KEY as *const u8 as *mut c_void);
+            push_gc_userdata(state, waker)?;
+            ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
+
+            Ok(WakerGuard(state))
+        }
+    }
+}
+
+#[cfg(feature = "async")]
+impl Drop for WakerGuard {
+    fn drop(&mut self) {
+        unsafe {
+            let state = self.0;
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 2);
+
+            ffi::lua_pushlightuserdata(state, &WAKER_REGISTRY_KEY as *const u8 as *mut c_void);
+            ffi::lua_pushnil(state);
+            ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
+        }
+    }
+}

src/types.rs

@@ -1,7 +1,11 @@
+use std::cell::RefCell;
 use std::os::raw::{c_int, c_void};
-use std::sync::{Arc, Mutex};
+use std::rc::Rc;
 use std::{fmt, mem, ptr};
 
+#[cfg(feature = "async")]
+use futures_core::future::LocalBoxFuture;
+
 use crate::error::Result;
 use crate::ffi;
 use crate::lua::Lua;
@@ -20,29 +24,28 @@ pub struct LightUserData(pub *mut c_void);
 pub(crate) type Callback<'lua, 'a> =
     Box<dyn Fn(&'lua Lua, MultiValue<'lua>) -> Result<MultiValue<'lua>> + 'a>;
 
+#[cfg(feature = "async")]
+pub(crate) type AsyncCallback<'lua, 'a> =
+    Box<dyn Fn(&'lua Lua, MultiValue<'lua>) -> LocalBoxFuture<'lua, Result<MultiValue<'lua>>> + 'a>;
+
 /// An auto generated key into the Lua registry.
 ///
-/// This is a handle to a value stored inside the Lua registry.  It is not directly usable like the
-/// `Table` or `Function` handle types, but since it doesn't hold a reference to a parent Lua and is
-/// Send + Sync + 'static, it is much more flexible and can be used in many situations where it is
-/// impossible to directly store a normal handle type.  It is not automatically garbage collected on
-/// Drop, but it can be removed with [`Lua::remove_registry_value`], and instances not manually
-/// removed can be garbage collected with [`Lua::expire_registry_values`].
+/// This is a handle to a value stored inside the Lua registry.  It is not automatically
+/// garbage collected on Drop, but it can be removed with [`Lua::remove_registry_value`],
+/// and instances not manually removed can be garbage collected with [`Lua::expire_registry_values`].
 ///
 /// Be warned, If you place this into Lua via a `UserData` type or a rust callback, it is *very
 /// easy* to accidentally cause reference cycles that the Lua garbage collector cannot resolve.
 /// Instead of placing a `RegistryKey` into a `UserData` type, prefer instead to use
-/// [`UserData::set_user_value`] / [`UserData::get_user_value`], and instead of moving a RegistryKey
-/// into a callback, prefer [`Lua::scope`].
+/// [`UserData::set_user_value`] / [`UserData::get_user_value`].
 ///
 /// [`Lua::remove_registry_value`]: struct.Lua.html#method.remove_registry_value
 /// [`Lua::expire_registry_values`]: struct.Lua.html#method.expire_registry_values
-/// [`Lua::scope`]: struct.Lua.html#method.scope
 /// [`UserData::set_user_value`]: struct.UserData.html#method.set_user_value
 /// [`UserData::get_user_value`]: struct.UserData.html#method.get_user_value
 pub struct RegistryKey {
     pub(crate) registry_id: c_int,
-    pub(crate) unref_list: Arc<Mutex<Option<Vec<c_int>>>>,
+    pub(crate) unref_list: Rc<RefCell<Option<Vec<c_int>>>>,
 }
 
 impl fmt::Debug for RegistryKey {
@@ -53,7 +56,8 @@ impl fmt::Debug for RegistryKey {
 
 impl Drop for RegistryKey {
     fn drop(&mut self) {
-        if let Some(list) = mlua_expect!(self.unref_list.lock(), "unref_list poisoned").as_mut() {
+        let mut unref_list = mlua_expect!(self.unref_list.try_borrow_mut(), "unref list borrowed");
+        if let Some(list) = unref_list.as_mut() {
             list.push(self.registry_id);
         }
     }

src/userdata.rs

@@ -1,5 +1,8 @@
 use std::cell::{Ref, RefCell, RefMut};
 
+#[cfg(feature = "async")]
+use std::future::Future;
+
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::function::Function;
@@ -134,7 +137,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + Fn(&'lua Lua, &T, A) -> Result<R>;
+        M: 'static + Fn(&'lua Lua, &T, A) -> Result<R>;
 
     /// Add a regular method which accepts a `&mut T` as the first parameter.
     ///
@@ -146,7 +149,23 @@ pub trait UserDataMethods<'lua, T: UserData> {
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + FnMut(&'lua Lua, &mut T, A) -> Result<R>;
+        M: 'static + FnMut(&'lua Lua, &mut T, A) -> Result<R>;
+
+    /// Add an async method which accepts a `T` as the first parameter and returns Future.
+    /// The passed `T` is cloned from the original value.
+    ///
+    /// Refer to [`add_method`] for more information about the implementation.
+    ///
+    /// [`add_method`]: #method.add_method
+    #[cfg(feature = "async")]
+    fn add_async_method<S, A, R, M, MR>(&mut self, name: &S, method: M)
+    where
+        T: Clone,
+        S: ?Sized + AsRef<[u8]>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        M: 'static + Fn(&'lua Lua, T, A) -> MR,
+        MR: 'static + Future<Output = Result<R>>;
 
     /// Add a regular method as a function which accepts generic arguments, the first argument will
     /// be a `UserData` of type T if the method is called with Lua method syntax:
@@ -162,7 +181,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + Fn(&'lua Lua, A) -> Result<R>;
+        F: 'static + Fn(&'lua Lua, A) -> Result<R>;
 
     /// Add a regular method as a mutable function which accepts generic arguments.
     ///
@@ -174,7 +193,23 @@ pub trait UserDataMethods<'lua, T: UserData> {
         S: ?Sized + AsRef<[u8]>,
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + FnMut(&'lua Lua, A) -> Result<R>;
+        F: 'static + FnMut(&'lua Lua, A) -> Result<R>;
+
+    /// Add a regular method as an async function which accepts generic arguments
+    /// and returns Future.
+    ///
+    /// This is an async version of [`add_function`].
+    ///
+    /// [`add_function`]: #method.add_function
+    #[cfg(feature = "async")]
+    fn add_async_function<S, A, R, F, FR>(&mut self, name: &S, function: F)
+    where
+        T: Clone,
+        S: ?Sized + AsRef<[u8]>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        F: 'static + Fn(&'lua Lua, A) -> FR,
+        FR: 'static + Future<Output = Result<R>>;
 
     /// Add a metamethod which accepts a `&T` as the first parameter.
     ///
@@ -188,7 +223,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + Fn(&'lua Lua, &T, A) -> Result<R>;
+        M: 'static + Fn(&'lua Lua, &T, A) -> Result<R>;
 
     /// Add a metamethod as a function which accepts a `&mut T` as the first parameter.
     ///
@@ -202,7 +237,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        M: 'static + Send + FnMut(&'lua Lua, &mut T, A) -> Result<R>;
+        M: 'static + FnMut(&'lua Lua, &mut T, A) -> Result<R>;
 
     /// Add a metamethod which accepts generic arguments.
     ///
@@ -213,7 +248,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + Fn(&'lua Lua, A) -> Result<R>;
+        F: 'static + Fn(&'lua Lua, A) -> Result<R>;
 
     /// Add a metamethod as a mutable function which accepts generic arguments.
     ///
@@ -224,7 +259,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
     where
         A: FromLuaMulti<'lua>,
         R: ToLuaMulti<'lua>,
-        F: 'static + Send + FnMut(&'lua Lua, A) -> Result<R>;
+        F: 'static + FnMut(&'lua Lua, A) -> Result<R>;
 }
 
 /// Trait for custom userdata types.
@@ -293,7 +328,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
 /// [`UserDataMethods`]: trait.UserDataMethods.html
 pub trait UserData: Sized {
     /// Adds custom methods and operators specific to this userdata.
-    fn add_methods<'lua, T: UserDataMethods<'lua, Self>>(_methods: &mut T) {}
+    fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(_methods: &mut M) {}
 }
 
 /// Handle to an internal Lua userdata for any type that implements [`UserData`].

src/util.rs

@@ -1,14 +1,20 @@
-use std::any::Any;
+use std::any::{Any, TypeId};
 use std::borrow::Cow;
+use std::cell::RefCell;
+use std::collections::HashMap;
 use std::fmt::Write;
 use std::os::raw::{c_char, c_int, c_void};
 use std::panic::{catch_unwind, resume_unwind, AssertUnwindSafe};
-use std::sync::Arc;
+use std::rc::Rc;
 use std::{mem, ptr, slice};
 
 use crate::error::{Error, Result};
 use crate::ffi;
 
+thread_local! {
+    static METATABLE_CACHE: RefCell<HashMap<TypeId, c_int>> = RefCell::new(HashMap::new());
+}
+
 // Checks that Lua has enough free stack space for future stack operations.  On failure, this will
 // panic with an internal error message.
 pub unsafe fn assert_stack(state: *mut ffi::lua_State, amount: c_int) {
@@ -175,8 +181,7 @@ pub unsafe fn pop_error(state: *mut ffi::lua_State, err_code: c_int) -> Error {
     if let Some(err) = get_wrapped_error(state, -1).as_ref() {
         ffi::lua_pop(state, 1);
         err.clone()
-    } else if is_wrapped_panic(state, -1) {
-        let panic = get_userdata::<WrappedPanic>(state, -1);
+    } else if let Some(panic) = get_gc_userdata::<WrappedPanic>(state, -1).as_mut() {
         if let Some(p) = (*panic).0.take() {
             resume_unwind(p);
         } else {
@@ -255,6 +260,41 @@ pub unsafe fn take_userdata<T>(state: *mut ffi::lua_State) -> T {
     ptr::read(ud)
 }
 
+// Pushes the userdata and attaches a metatable with __gc method
+// Internally uses 5 stack spaces, does not call checkstack
+pub unsafe fn push_gc_userdata<T: Any>(state: *mut ffi::lua_State, t: T) -> Result<()> {
+    push_meta_gc_userdata::<T, T>(state, t)
+}
+
+pub unsafe fn push_meta_gc_userdata<MT: Any, T>(state: *mut ffi::lua_State, t: T) -> Result<()> {
+    let ud = protect_lua_closure(state, 0, 1, move |state| {
+        ffi::lua_newuserdata(state, mem::size_of::<T>()) as *mut T
+    })?;
+    ptr::write(ud, t);
+    get_gc_metatable_for::<MT>(state);
+    ffi::lua_setmetatable(state, -2);
+    Ok(())
+}
+
+// Uses 2 stack spaces, does not call checkstack
+pub unsafe fn get_gc_userdata<T: Any>(state: *mut ffi::lua_State, index: c_int) -> *mut T {
+    get_meta_gc_userdata::<T, T>(state, index)
+}
+
+pub unsafe fn get_meta_gc_userdata<MT: Any, T>(state: *mut ffi::lua_State, index: c_int) -> *mut T {
+    let ud = ffi::lua_touserdata(state, index) as *mut T;
+    if ud.is_null() || ffi::lua_getmetatable(state, index) == 0 {
+        return ptr::null_mut();
+    }
+    get_gc_metatable_for::<MT>(state);
+    let res = ffi::lua_rawequal(state, -1, -2) != 0;
+    ffi::lua_pop(state, 2);
+    if !res {
+        return ptr::null_mut();
+    }
+    ud
+}
+
 // Populates the given table with the appropriate members to be a userdata metatable for the given
 // type.  This function takes the given table at the `metatable` index, and adds an appropriate __gc
 // member to it for the given type and a __metatable entry to protect the table from script access.
@@ -380,14 +420,14 @@ where
         Ok(Err(err)) => {
             ffi::lua_settop(state, 1);
             ptr::write(ud as *mut WrappedError, WrappedError(err));
-            get_error_metatable(state);
+            get_gc_metatable_for::<WrappedError>(state);
             ffi::lua_setmetatable(state, -2);
             ffi::lua_error(state)
         }
         Err(p) => {
             ffi::lua_settop(state, 1);
             ptr::write(ud as *mut WrappedPanic, WrappedPanic(Some(p)));
-            get_panic_metatable(state);
+            get_gc_metatable_for::<WrappedPanic>(state);
             ffi::lua_setmetatable(state, -2);
             ffi::lua_error(state)
         }
@@ -428,12 +468,12 @@ pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
             ud,
             WrappedError(Error::CallbackError {
                 traceback,
-                cause: Arc::new(error),
+                cause: Rc::new(error),
             }),
         );
-        get_error_metatable(state);
+        get_gc_metatable_for::<WrappedError>(state);
         ffi::lua_setmetatable(state, -2);
-    } else if !is_wrapped_panic(state, -1) {
+    } else if let None = get_gc_userdata::<WrappedPanic>(state, -1).as_ref() {
         if ffi::lua_checkstack(state, LUA_TRACEBACK_STACK) != 0 {
             let s = ffi::luaL_tolstring(state, -1, ptr::null_mut());
             ffi::luaL_traceback(state, state, s, 0);
@@ -443,68 +483,72 @@ pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
     1
 }
 
-// Does not call lua_checkstack, uses 2 stack spaces.
-#[cfg(any(feature = "lua51", feature = "luajit"))]
-pub unsafe fn set_main_state(state: *mut ffi::lua_State) {
-    ffi::lua_pushlightuserdata(state, &MAIN_THREAD_REGISTRY_KEY as *const u8 as *mut c_void);
-    ffi::lua_pushthread(state);
-    ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
-}
-
 // Does not call lua_checkstack, uses 1 stack space.
 pub unsafe fn get_main_state(state: *mut ffi::lua_State) -> *mut ffi::lua_State {
     #[cfg(any(feature = "lua53", feature = "lua52"))]
-    ffi::lua_rawgeti(state, ffi::LUA_REGISTRYINDEX, ffi::LUA_RIDX_MAINTHREAD);
-    #[cfg(any(feature = "lua51", feature = "luajit"))]
     {
-        ffi::lua_pushlightuserdata(state, &MAIN_THREAD_REGISTRY_KEY as *const u8 as *mut c_void);
-        ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
+        ffi::lua_rawgeti(state, ffi::LUA_REGISTRYINDEX, ffi::LUA_RIDX_MAINTHREAD);
+        let main_state = ffi::lua_tothread(state, -1);
+        ffi::lua_pop(state, 1);
+        main_state
     }
-    let main_state = ffi::lua_tothread(state, -1);
-    ffi::lua_pop(state, 1);
-    main_state
+    #[cfg(any(feature = "lua51", feature = "luajit"))]
+    state
 }
 
 // Pushes a WrappedError to the top of the stack.  Uses two stack spaces and does not call
 // lua_checkstack.
 pub unsafe fn push_wrapped_error(state: *mut ffi::lua_State, err: Error) -> Result<()> {
-    let ud = protect_lua_closure(state, 0, 1, move |state| {
-        ffi::lua_newuserdata(state, mem::size_of::<WrappedError>()) as *mut WrappedError
-    })?;
-    ptr::write(ud, WrappedError(err));
-    get_error_metatable(state);
-    ffi::lua_setmetatable(state, -2);
-    Ok(())
+    push_gc_userdata::<WrappedError>(state, WrappedError(err))
 }
 
 // Checks if the value at the given index is a WrappedError, and if it is returns a pointer to it,
 // otherwise returns null.  Uses 2 stack spaces and does not call lua_checkstack.
 pub unsafe fn get_wrapped_error(state: *mut ffi::lua_State, index: c_int) -> *const Error {
-    let userdata = ffi::lua_touserdata(state, index);
-    if userdata.is_null() {
+    let ud = get_gc_userdata::<WrappedError>(state, index);
+    if ud.is_null() {
         return ptr::null();
     }
+    &(*ud).0
+}
 
-    if ffi::lua_getmetatable(state, index) == 0 {
-        return ptr::null();
+// Initialize the internal (with __gc) metatable for a type T
+pub unsafe fn init_gc_metatable_for<T: Any>(
+    state: *mut ffi::lua_State,
+    customize_fn: Option<fn(*mut ffi::lua_State)>,
+) {
+    let type_id = TypeId::of::<T>();
+
+    ffi::lua_newtable(state);
+
+    ffi::lua_pushstring(state, cstr!("__gc"));
+    ffi::lua_pushcfunction(state, userdata_destructor::<T>);
+    ffi::lua_rawset(state, -3);
+
+    ffi::lua_pushstring(state, cstr!("__metatable"));
+    ffi::lua_pushboolean(state, 0);
+    ffi::lua_rawset(state, -3);
+
+    if let Some(f) = customize_fn {
+        f(state)
     }
 
-    get_error_metatable(state);
-    let res = ffi::lua_rawequal(state, -1, -2) != 0;
-    ffi::lua_pop(state, 2);
+    let ref_addr = ffi::luaL_ref(state, ffi::LUA_REGISTRYINDEX);
+    METATABLE_CACHE.with(|mc| mc.borrow_mut().insert(type_id, ref_addr));
+}
 
-    if res {
-        &(*get_userdata::<WrappedError>(state, -1)).0
-    } else {
-        ptr::null()
-    }
+pub unsafe fn get_gc_metatable_for<T: Any>(state: *mut ffi::lua_State) {
+    let type_id = TypeId::of::<T>();
+    let ref_addr = METATABLE_CACHE
+        .with(|mc| *mlua_expect!(mc.borrow().get(&type_id), "gc metatable does not exist"));
+    ffi::lua_rawgeti(state, ffi::LUA_REGISTRYINDEX, ref_addr as ffi::lua_Integer);
 }
 
 // Initialize the error, panic, and destructed userdata metatables.
 pub unsafe fn init_error_registry(state: *mut ffi::lua_State) {
     assert_stack(state, 8);
 
-    // Create error metatable
+    // Create error and panic metatables
 
     unsafe extern "C" fn error_tostring(state: *mut ffi::lua_State) -> c_int {
         let err_buf = callback_error(state, |_| {
@@ -524,8 +568,7 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) {
                 // kind of recursive error structure?)
                 let _ = write!(&mut (*err_buf), "{}", error);
                 Ok(err_buf)
-            } else if is_wrapped_panic(state, -1) {
-                let panic = get_userdata::<WrappedPanic>(state, -1);
+            } else if let Some(panic) = get_gc_userdata::<WrappedPanic>(state, -1).as_ref() {
                 if let Some(ref p) = (*panic).0 {
                     ffi::lua_pushlightuserdata(
                         state,
@@ -564,56 +607,31 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) {
         1
     }
 
-    ffi::lua_pushlightuserdata(
+    init_gc_metatable_for::<WrappedError>(
         state,
-        &ERROR_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
+        Some(|state| {
+            ffi::lua_pushstring(state, cstr!("__tostring"));
+            ffi::lua_pushcfunction(state, error_tostring);
+            ffi::lua_rawset(state, -3);
+        }),
     );
-    ffi::lua_newtable(state);
 
-    ffi::lua_pushstring(state, cstr!("__gc"));
-    ffi::lua_pushcfunction(state, userdata_destructor::<WrappedError>);
-    ffi::lua_rawset(state, -3);
-
-    ffi::lua_pushstring(state, cstr!("__tostring"));
-    ffi::lua_pushcfunction(state, error_tostring);
-    ffi::lua_rawset(state, -3);
-
-    ffi::lua_pushstring(state, cstr!("__metatable"));
-    ffi::lua_pushboolean(state, 0);
-    ffi::lua_rawset(state, -3);
-
-    ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
-
-    // Create panic metatable
-
-    ffi::lua_pushlightuserdata(
+    init_gc_metatable_for::<WrappedPanic>(
         state,
-        &PANIC_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
+        Some(|state| {
+            ffi::lua_pushstring(state, cstr!("__tostring"));
+            ffi::lua_pushcfunction(state, error_tostring);
+            ffi::lua_rawset(state, -3);
+        }),
     );
-    ffi::lua_newtable(state);
-
-    ffi::lua_pushstring(state, cstr!("__gc"));
-    ffi::lua_pushcfunction(state, userdata_destructor::<WrappedPanic>);
-    ffi::lua_rawset(state, -3);
-
-    ffi::lua_pushstring(state, cstr!("__tostring"));
-    ffi::lua_pushcfunction(state, error_tostring);
-    ffi::lua_rawset(state, -3);
-
-    ffi::lua_pushstring(state, cstr!("__metatable"));
-    ffi::lua_pushboolean(state, 0);
-    ffi::lua_rawset(state, -3);
-
-    ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
 
     // Create destructed userdata metatable
 
     unsafe extern "C" fn destructed_error(state: *mut ffi::lua_State) -> c_int {
         ffi::luaL_checkstack(state, 2, ptr::null());
         let ud = ffi::lua_newuserdata(state, mem::size_of::<WrappedError>()) as *mut WrappedError;
-
         ptr::write(ud, WrappedError(Error::CallbackDestructed));
-        get_error_metatable(state);
+        get_gc_metatable_for::<WrappedError>(state);
         ffi::lua_setmetatable(state, -2);
         ffi::lua_error(state)
     }
@@ -709,40 +727,6 @@ unsafe fn to_string<'a>(state: *mut ffi::lua_State, index: c_int) -> Cow<'a, str
     }
 }
 
-// Checks if the value at the given index is a WrappedPanic.  Uses 2 stack spaces and does not call
-// lua_checkstack.
-unsafe fn is_wrapped_panic(state: *mut ffi::lua_State, index: c_int) -> bool {
-    let userdata = ffi::lua_touserdata(state, index);
-    if userdata.is_null() {
-        return false;
-    }
-
-    if ffi::lua_getmetatable(state, index) == 0 {
-        return false;
-    }
-
-    get_panic_metatable(state);
-    let res = ffi::lua_rawequal(state, -1, -2) != 0;
-    ffi::lua_pop(state, 2);
-    res
-}
-
-unsafe fn get_error_metatable(state: *mut ffi::lua_State) {
-    ffi::lua_pushlightuserdata(
-        state,
-        &ERROR_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
-    );
-    ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
-}
-
-unsafe fn get_panic_metatable(state: *mut ffi::lua_State) {
-    ffi::lua_pushlightuserdata(
-        state,
-        &PANIC_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
-    );
-    ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
-}
-
 unsafe fn get_destructed_userdata_metatable(state: *mut ffi::lua_State) {
     ffi::lua_pushlightuserdata(
         state,
@@ -751,9 +735,5 @@ unsafe fn get_destructed_userdata_metatable(state: *mut ffi::lua_State) {
     ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);
 }
 
-#[cfg(any(feature = "lua51", feature = "luajit"))]
-static MAIN_THREAD_REGISTRY_KEY: u8 = 0;
-static ERROR_METATABLE_REGISTRY_KEY: u8 = 0;
-static PANIC_METATABLE_REGISTRY_KEY: u8 = 0;
 static DESTRUCTED_USERDATA_METATABLE: u8 = 0;
 static ERROR_PRINT_BUFFER_KEY: u8 = 0;

tests/compile_fail/lua_norefunwindsafe.stderr

@@ -10,6 +10,21 @@ error[E0277]: the type `std::cell::UnsafeCell<()>` may contain interior mutabili
     = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
     = note: required because it appears within the type `[closure@$DIR/tests/compile_fail/lua_norefunwindsafe.rs:7:18: 7:48 lua:&mlua::lua::Lua]`
 
+error[E0277]: the type `std::cell::UnsafeCell<usize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+   --> $DIR/lua_norefunwindsafe.rs:7:5
+    |
+7   |     catch_unwind(|| lua.create_table().unwrap());
+    |     ^^^^^^^^^^^^ `std::cell::UnsafeCell<usize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+    |
+    = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<usize>`
+    = note: required because it appears within the type `std::cell::Cell<usize>`
+    = note: required because it appears within the type `std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::marker::PhantomData<std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>>`
+    = note: required because it appears within the type `std::rc::Rc<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `mlua::lua::Lua`
+    = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
+    = note: required because it appears within the type `[closure@$DIR/tests/compile_fail/lua_norefunwindsafe.rs:7:18: 7:48 lua:&mlua::lua::Lua]`
+
 error[E0277]: the type `std::cell::UnsafeCell<mlua::lua::ExtraData>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
    --> $DIR/lua_norefunwindsafe.rs:7:5
     |
@@ -18,9 +33,9 @@ error[E0277]: the type `std::cell::UnsafeCell<mlua::lua::ExtraData>` may contain
     |
     = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<mlua::lua::ExtraData>`
     = note: required because it appears within the type `std::cell::RefCell<mlua::lua::ExtraData>`
-    = note: required because it appears within the type `alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>`
-    = note: required because it appears within the type `std::marker::PhantomData<alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>>`
-    = note: required because it appears within the type `std::sync::Arc<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::marker::PhantomData<std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>>`
+    = note: required because it appears within the type `std::rc::Rc<std::cell::RefCell<mlua::lua::ExtraData>>`
     = note: required because it appears within the type `mlua::lua::Lua`
     = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
     = note: required because it appears within the type `[closure@$DIR/tests/compile_fail/lua_norefunwindsafe.rs:7:18: 7:48 lua:&mlua::lua::Lua]`
@@ -34,9 +49,9 @@ error[E0277]: the type `std::cell::UnsafeCell<isize>` may contain interior mutab
     = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<isize>`
     = note: required because it appears within the type `std::cell::Cell<isize>`
     = note: required because it appears within the type `std::cell::RefCell<mlua::lua::ExtraData>`
-    = note: required because it appears within the type `alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>`
-    = note: required because it appears within the type `std::marker::PhantomData<alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>>`
-    = note: required because it appears within the type `std::sync::Arc<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::marker::PhantomData<std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>>`
+    = note: required because it appears within the type `std::rc::Rc<std::cell::RefCell<mlua::lua::ExtraData>>`
     = note: required because it appears within the type `mlua::lua::Lua`
     = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
     = note: required because it appears within the type `[closure@$DIR/tests/compile_fail/lua_norefunwindsafe.rs:7:18: 7:48 lua:&mlua::lua::Lua]`

tests/compile_fail/ref_nounwindsafe.stderr

@@ -12,6 +12,23 @@ error[E0277]: the type `std::cell::UnsafeCell<()>` may contain interior mutabili
     = note: required because it appears within the type `mlua::table::Table<'_>`
     = note: required because it appears within the type `[closure@$DIR/tests/compile_fail/ref_nounwindsafe.rs:8:18: 8:54 table:mlua::table::Table<'_>]`
 
+error[E0277]: the type `std::cell::UnsafeCell<usize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+   --> $DIR/ref_nounwindsafe.rs:8:5
+    |
+8   |     catch_unwind(move || table.set("a", "b").unwrap());
+    |     ^^^^^^^^^^^^ `std::cell::UnsafeCell<usize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+    |
+    = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<usize>`
+    = note: required because it appears within the type `std::cell::Cell<usize>`
+    = note: required because it appears within the type `std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::marker::PhantomData<std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>>`
+    = note: required because it appears within the type `std::rc::Rc<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `mlua::lua::Lua`
+    = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
+    = note: required because it appears within the type `mlua::types::LuaRef<'_>`
+    = note: required because it appears within the type `mlua::table::Table<'_>`
+    = note: required because it appears within the type `[closure@$DIR/tests/compile_fail/ref_nounwindsafe.rs:8:18: 8:54 table:mlua::table::Table<'_>]`
+
 error[E0277]: the type `std::cell::UnsafeCell<mlua::lua::ExtraData>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
    --> $DIR/ref_nounwindsafe.rs:8:5
     |
@@ -20,9 +37,9 @@ error[E0277]: the type `std::cell::UnsafeCell<mlua::lua::ExtraData>` may contain
     |
     = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<mlua::lua::ExtraData>`
     = note: required because it appears within the type `std::cell::RefCell<mlua::lua::ExtraData>`
-    = note: required because it appears within the type `alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>`
-    = note: required because it appears within the type `std::marker::PhantomData<alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>>`
-    = note: required because it appears within the type `std::sync::Arc<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::marker::PhantomData<std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>>`
+    = note: required because it appears within the type `std::rc::Rc<std::cell::RefCell<mlua::lua::ExtraData>>`
     = note: required because it appears within the type `mlua::lua::Lua`
     = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
     = note: required because it appears within the type `mlua::types::LuaRef<'_>`
@@ -38,9 +55,9 @@ error[E0277]: the type `std::cell::UnsafeCell<isize>` may contain interior mutab
     = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<isize>`
     = note: required because it appears within the type `std::cell::Cell<isize>`
     = note: required because it appears within the type `std::cell::RefCell<mlua::lua::ExtraData>`
-    = note: required because it appears within the type `alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>`
-    = note: required because it appears within the type `std::marker::PhantomData<alloc::sync::ArcInner<std::cell::RefCell<mlua::lua::ExtraData>>>`
-    = note: required because it appears within the type `std::sync::Arc<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>`
+    = note: required because it appears within the type `std::marker::PhantomData<std::rc::RcBox<std::cell::RefCell<mlua::lua::ExtraData>>>`
+    = note: required because it appears within the type `std::rc::Rc<std::cell::RefCell<mlua::lua::ExtraData>>`
     = note: required because it appears within the type `mlua::lua::Lua`
     = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
     = note: required because it appears within the type `mlua::types::LuaRef<'_>`

tests/compile_fail/scope_callback_capture.rs

@@ -1,22 +0,0 @@
-use mlua::{Lua, Table, Result};
-
-struct Test {
-    field: i32,
-}
-
-fn main() {
-    let lua = Lua::new();
-    lua.scope(|scope| -> Result<()> {
-        let mut inner: Option<Table> = None;
-        let f = scope
-            .create_function_mut(move |lua, t: Table| {
-                if let Some(old) = inner.take() {
-                    // Access old callback `Lua`.
-                }
-                inner = Some(t);
-                Ok(())
-            })?;
-        f.call::<_, ()>(lua.create_table()?)?;
-        Ok(())
-    });
-}

tests/compile_fail/scope_callback_capture.stderr

@@ -1,45 +0,0 @@
-error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
-  --> $DIR/scope_callback_capture.rs:12:14
-   |
-12 |             .create_function_mut(move |lua, t: Table| {
-   |              ^^^^^^^^^^^^^^^^^^^
-   |
-note: first, the lifetime cannot outlive the anonymous lifetime #2 defined on the body at 9:15...
-  --> $DIR/scope_callback_capture.rs:9:15
-   |
-9  |       lua.scope(|scope| -> Result<()> {
-   |  _______________^
-10 | |         let mut inner: Option<Table> = None;
-11 | |         let f = scope
-12 | |             .create_function_mut(move |lua, t: Table| {
-...  |
-20 | |         Ok(())
-21 | |     });
-   | |_____^
-note: ...so that reference does not outlive borrowed content
-  --> $DIR/scope_callback_capture.rs:11:17
-   |
-11 |         let f = scope
-   |                 ^^^^^
-note: but, the lifetime must be valid for the method call at 9:5...
-  --> $DIR/scope_callback_capture.rs:9:5
-   |
-9  | /     lua.scope(|scope| -> Result<()> {
-10 | |         let mut inner: Option<Table> = None;
-11 | |         let f = scope
-12 | |             .create_function_mut(move |lua, t: Table| {
-...  |
-20 | |         Ok(())
-21 | |     });
-   | |______^
-note: ...so that a type/lifetime parameter is in scope here
-  --> $DIR/scope_callback_capture.rs:9:5
-   |
-9  | /     lua.scope(|scope| -> Result<()> {
-10 | |         let mut inner: Option<Table> = None;
-11 | |         let f = scope
-12 | |             .create_function_mut(move |lua, t: Table| {
-...  |
-20 | |         Ok(())
-21 | |     });
-   | |______^

tests/compile_fail/scope_callback_inner.rs

@@ -1,19 +0,0 @@
-use mlua::{Lua, Table, Result};
-
-struct Test {
-    field: i32,
-}
-
-fn main() {
-    let lua = Lua::new();
-    lua.scope(|scope| -> Result<()> {
-        let mut inner: Option<Table> = None;
-        let f = scope
-            .create_function_mut(|_, t: Table| {
-                inner = Some(t);
-                Ok(())
-            })?;
-        f.call::<_, ()>(lua.create_table()?)?;
-        Ok(())
-    });
-}

tests/compile_fail/scope_callback_inner.stderr

@@ -1,45 +0,0 @@
-error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
-  --> $DIR/scope_callback_inner.rs:12:14
-   |
-12 |             .create_function_mut(|_, t: Table| {
-   |              ^^^^^^^^^^^^^^^^^^^
-   |
-note: first, the lifetime cannot outlive the anonymous lifetime #2 defined on the body at 9:15...
-  --> $DIR/scope_callback_inner.rs:9:15
-   |
-9  |       lua.scope(|scope| -> Result<()> {
-   |  _______________^
-10 | |         let mut inner: Option<Table> = None;
-11 | |         let f = scope
-12 | |             .create_function_mut(|_, t: Table| {
-...  |
-17 | |         Ok(())
-18 | |     });
-   | |_____^
-note: ...so that reference does not outlive borrowed content
-  --> $DIR/scope_callback_inner.rs:11:17
-   |
-11 |         let f = scope
-   |                 ^^^^^
-note: but, the lifetime must be valid for the method call at 9:5...
-  --> $DIR/scope_callback_inner.rs:9:5
-   |
-9  | /     lua.scope(|scope| -> Result<()> {
-10 | |         let mut inner: Option<Table> = None;
-11 | |         let f = scope
-12 | |             .create_function_mut(|_, t: Table| {
-...  |
-17 | |         Ok(())
-18 | |     });
-   | |______^
-note: ...so that a type/lifetime parameter is in scope here
-  --> $DIR/scope_callback_inner.rs:9:5
-   |
-9  | /     lua.scope(|scope| -> Result<()> {
-10 | |         let mut inner: Option<Table> = None;
-11 | |         let f = scope
-12 | |             .create_function_mut(|_, t: Table| {
-...  |
-17 | |         Ok(())
-18 | |     });
-   | |______^

tests/compile_fail/scope_callback_outer.rs

@@ -1,19 +0,0 @@
-use mlua::{Lua, Table, Result};
-
-struct Test {
-    field: i32,
-}
-
-fn main() {
-    let lua = Lua::new();
-    let mut outer: Option<Table> = None;
-    lua.scope(|scope| -> Result<()> {
-        let f = scope
-            .create_function_mut(|_, t: Table| {
-                outer = Some(t);
-                Ok(())
-            })?;
-        f.call::<_, ()>(lua.create_table()?)?;
-        Ok(())
-    });
-}

tests/compile_fail/scope_callback_outer.stderr

@@ -1,11 +0,0 @@
-error: borrowed data cannot be stored outside of its closure
-  --> $DIR/scope_callback_outer.rs:11:17
-   |
-9  |     let mut outer: Option<Table> = None;
-   |         --------- ...so that variable is valid at time of its declaration
-10 |     lua.scope(|scope| -> Result<()> {
-   |               --------------------- borrowed data cannot outlive this closure
-11 |         let f = scope
-   |                 ^^^^^ cannot be stored outside of its closure
-12 |             .create_function_mut(|_, t: Table| {
-   |              ------------------- cannot infer an appropriate lifetime...

tests/compile_fail/scope_invariance.rs

@@ -1,23 +0,0 @@
-use mlua::{Lua, Result};
-
-struct Test {
-    field: i32,
-}
-
-fn main() {
-    let lua = Lua::new();
-    lua.scope(|scope| -> Result<()> {
-        let f = {
-            let mut test = Test { field: 0 };
-
-            scope
-                .create_function_mut(|_, ()| {
-                    test.field = 42;
-                    //~^ error: `test` does not live long enough
-                    Ok(())
-                })?
-        };
-
-        f.call::<_, ()>(())
-    });
-}

tests/compile_fail/scope_invariance.stderr

@@ -1,25 +0,0 @@
-error[E0373]: closure may outlive the current function, but it borrows `test`, which is owned by the current function
-  --> $DIR/scope_invariance.rs:14:38
-   |
-9  |     lua.scope(|scope| -> Result<()> {
-   |                ----- has type `&mlua::scope::Scope<'_, '1>`
-...
-14 |                 .create_function_mut(|_, ()| {
-   |                                      ^^^^^^^ may outlive borrowed value `test`
-15 |                     test.field = 42;
-   |                     ---- `test` is borrowed here
-   |
-note: function requires argument type to outlive `'1`
-  --> $DIR/scope_invariance.rs:13:13
-   |
-13 | /             scope
-14 | |                 .create_function_mut(|_, ()| {
-15 | |                     test.field = 42;
-16 | |                     //~^ error: `test` does not live long enough
-17 | |                     Ok(())
-18 | |                 })?
-   | |__________________^
-help: to force the closure to take ownership of `test` (and any other referenced variables), use the `move` keyword
-   |
-14 |                 .create_function_mut(move |_, ()| {
-   |                                      ^^^^^^^^^^^^

tests/compile_fail/scope_mutable_aliasing.rs

@@ -1,15 +0,0 @@
-use mlua::{Lua, UserData, Result};
-
-struct MyUserData<'a>(&'a mut i32);
-impl<'a> UserData for MyUserData<'a> {}
-
-fn main() {
-    let mut i = 1;
-
-    let lua = Lua::new();
-    lua.scope(|scope| -> Result<()> {
-        let _a = scope.create_nonstatic_userdata(MyUserData(&mut i))?;
-        let _b = scope.create_nonstatic_userdata(MyUserData(&mut i))?;
-        Ok(())
-    });
-}

tests/compile_fail/scope_mutable_aliasing.stderr

@@ -1,9 +0,0 @@
-error[E0499]: cannot borrow `i` as mutable more than once at a time
-  --> $DIR/scope_mutable_aliasing.rs:12:61
-   |
-11 |         let _a = scope.create_nonstatic_userdata(MyUserData(&mut i))?;
-   |                                                             ------ first mutable borrow occurs here
-12 |         let _b = scope.create_nonstatic_userdata(MyUserData(&mut i))?;
-   |                        -------------------------            ^^^^^^ second mutable borrow occurs here
-   |                        |
-   |                        first borrow later used by call

tests/compile_fail/scope_userdata_borrow.rs

@@ -1,20 +0,0 @@
-use mlua::{Lua, UserData, Result};
-
-struct MyUserData<'a>(&'a i32);
-impl<'a> UserData for MyUserData<'a> {}
-
-fn main() {
-    // Should not allow userdata borrow to outlive lifetime of AnyUserData handle
-
-    let igood = 1;
-
-    let lua = Lua::new();
-    lua.scope(|scope| -> Result<()> {
-        let _ugood = scope.create_nonstatic_userdata(MyUserData(&igood))?;
-        let _ubad = {
-            let ibad = 42;
-            scope.create_nonstatic_userdata(MyUserData(&ibad))?;
-        };
-        Ok(())
-    });
-}

tests/compile_fail/scope_userdata_borrow.stderr

@@ -1,13 +0,0 @@
-error[E0597]: `ibad` does not live long enough
-  --> $DIR/scope_userdata_borrow.rs:16:56
-   |
-12 |     lua.scope(|scope| -> Result<()> {
-   |                ----- has type `&mlua::scope::Scope<'_, '1>`
-...
-16 |             scope.create_nonstatic_userdata(MyUserData(&ibad))?;
-   |             -------------------------------------------^^^^^--
-   |             |                                          |
-   |             |                                          borrowed value does not live long enough
-   |             argument requires that `ibad` is borrowed for `'1`
-17 |         };
-   |         - `ibad` dropped here while still borrowed

tests/function.rs

@@ -1,4 +1,10 @@
-use mlua::{Function, Lua, Result, String};
+#![allow(unused_imports)]
+
+use std::{string::String as StdString, time::Duration};
+
+use futures_executor::block_on;
+
+use mlua::{Error, Function, Lua, Result, String, Thread};
 
 #[test]
 fn test_function() -> Result<()> {
@@ -75,3 +81,34 @@ fn test_rust_function() -> Result<()> {
 
     Ok(())
 }
+
+#[cfg(feature = "async")]
+#[tokio::test]
+async fn test_async_function() -> Result<()> {
+    let lua = Lua::new();
+
+    let f = lua.create_async_function(move |_lua, n: u64| async move {
+        futures_timer::Delay::new(Duration::from_secs(n)).await;
+        Ok("hello")
+    })?;
+    lua.globals().set("rust_async_sleep", f)?;
+
+    let thread = lua
+        .load(
+            r#"
+            coroutine.create(function ()
+                ret = rust_async_sleep(1)
+                assert(ret == "hello")
+                coroutine.yield()
+                return "world"
+            end)
+        "#,
+        )
+        .eval::<Thread>()?;
+
+    let fut = thread.into_async(());
+    let ret: StdString = fut.await?;
+    assert_eq!(ret, "world");
+
+    Ok(())
+}

tests/memory.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::rc::Rc;
 
 use mlua::{Lua, Result, UserData};
 
@@ -16,17 +16,17 @@ fn test_gc_control() -> Result<()> {
         assert!(lua.gc_is_running());
     }
 
-    struct MyUserdata(Arc<()>);
+    struct MyUserdata(Rc<()>);
     impl UserData for MyUserdata {}
 
-    let rc = Arc::new(());
+    let rc = Rc::new(());
     globals.set("userdata", lua.create_userdata(MyUserdata(rc.clone()))?)?;
     globals.raw_remove("userdata")?;
 
-    assert_eq!(Arc::strong_count(&rc), 2);
+    assert_eq!(Rc::strong_count(&rc), 2);
     lua.gc_collect()?;
     lua.gc_collect()?;
-    assert_eq!(Arc::strong_count(&rc), 1);
+    assert_eq!(Rc::strong_count(&rc), 1);
 
     Ok(())
 }

tests/scope.rs

@@ -1,231 +0,0 @@
-use std::cell::Cell;
-use std::rc::Rc;
-
-use mlua::{Error, Function, Lua, MetaMethod, Result, String, UserData, UserDataMethods};
-
-#[test]
-fn scope_func() -> Result<()> {
-    let lua = Lua::new();
-
-    let rc = Rc::new(Cell::new(0));
-    lua.scope(|scope| {
-        let r = rc.clone();
-        let f = scope.create_function(move |_, ()| {
-            r.set(42);
-            Ok(())
-        })?;
-        lua.globals().set("bad", f.clone())?;
-        f.call::<_, ()>(())?;
-        assert_eq!(Rc::strong_count(&rc), 2);
-        Ok(())
-    })?;
-    assert_eq!(rc.get(), 42);
-    assert_eq!(Rc::strong_count(&rc), 1);
-
-    match lua.globals().get::<_, Function>("bad")?.call::<_, ()>(()) {
-        Err(Error::CallbackError { .. }) => {}
-        r => panic!("improper return for destructed function: {:?}", r),
-    };
-
-    Ok(())
-}
-
-#[test]
-fn scope_drop() -> Result<()> {
-    let lua = Lua::new();
-
-    struct MyUserdata(Rc<()>);
-    impl UserData for MyUserdata {
-        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_method("method", |_, _, ()| Ok(()));
-        }
-    }
-
-    let rc = Rc::new(());
-
-    lua.scope(|scope| {
-        lua.globals().set(
-            "test",
-            scope.create_static_userdata(MyUserdata(rc.clone()))?,
-        )?;
-        assert_eq!(Rc::strong_count(&rc), 2);
-        Ok(())
-    })?;
-    assert_eq!(Rc::strong_count(&rc), 1);
-
-    match lua.load("test:method()").exec() {
-        Err(Error::CallbackError { .. }) => {}
-        r => panic!("improper return for destructed userdata: {:?}", r),
-    };
-
-    Ok(())
-}
-
-#[test]
-fn scope_capture() -> Result<()> {
-    let lua = Lua::new();
-
-    let mut i = 0;
-    lua.scope(|scope| {
-        scope
-            .create_function_mut(|_, ()| {
-                i = 42;
-                Ok(())
-            })?
-            .call::<_, ()>(())
-    })?;
-    assert_eq!(i, 42);
-
-    Ok(())
-}
-
-#[test]
-fn outer_lua_access() -> Result<()> {
-    let lua = Lua::new();
-
-    let table = lua.create_table()?;
-    lua.scope(|scope| {
-        scope
-            .create_function_mut(|_, ()| table.set("a", "b"))?
-            .call::<_, ()>(())
-    })?;
-    assert_eq!(table.get::<_, String>("a")?, "b");
-
-    Ok(())
-}
-
-#[test]
-fn scope_userdata_methods() -> Result<()> {
-    struct MyUserData<'a>(&'a Cell<i64>);
-
-    impl<'a> UserData for MyUserData<'a> {
-        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_method("inc", |_, data, ()| {
-                data.0.set(data.0.get() + 1);
-                Ok(())
-            });
-
-            methods.add_method("dec", |_, data, ()| {
-                data.0.set(data.0.get() - 1);
-                Ok(())
-            });
-        }
-    }
-
-    let lua = Lua::new();
-
-    let i = Cell::new(42);
-    let f: Function = lua
-        .load(
-            r#"
-            function(u)
-                u:inc()
-                u:inc()
-                u:inc()
-                u:dec()
-            end
-        "#,
-        )
-        .eval()?;
-
-    lua.scope(|scope| f.call::<_, ()>(scope.create_nonstatic_userdata(MyUserData(&i))?))?;
-
-    assert_eq!(i.get(), 44);
-
-    Ok(())
-}
-
-#[test]
-fn scope_userdata_functions() -> Result<()> {
-    struct MyUserData<'a>(&'a i64);
-
-    impl<'a> UserData for MyUserData<'a> {
-        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_meta_function(MetaMethod::Add, |lua, ()| {
-                let globals = lua.globals();
-                globals.set("i", globals.get::<_, i64>("i")? + 1)?;
-                Ok(())
-            });
-            methods.add_meta_function(MetaMethod::Sub, |lua, ()| {
-                let globals = lua.globals();
-                globals.set("i", globals.get::<_, i64>("i")? + 1)?;
-                Ok(())
-            });
-        }
-    }
-
-    let lua = Lua::new();
-
-    let dummy = 0;
-    let f = lua
-        .load(
-            r#"
-            i = 0
-            return function(u)
-                _ = u + u
-                _ = u - 1
-                _ = 1 + u
-            end
-        "#,
-        )
-        .eval::<Function>()?;
-
-    lua.scope(|scope| f.call::<_, ()>(scope.create_nonstatic_userdata(MyUserData(&dummy))?))?;
-
-    assert_eq!(lua.globals().get::<_, i64>("i")?, 3);
-
-    Ok(())
-}
-
-#[test]
-fn scope_userdata_mismatch() -> Result<()> {
-    struct MyUserData<'a>(&'a Cell<i64>);
-
-    impl<'a> UserData for MyUserData<'a> {
-        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_method("inc", |_, data, ()| {
-                data.0.set(data.0.get() + 1);
-                Ok(())
-            });
-        }
-    }
-
-    let lua = Lua::new();
-
-    lua.load(
-        r#"
-        function okay(a, b)
-            a.inc(a)
-            b.inc(b)
-        end
-
-        function bad(a, b)
-            a.inc(b)
-        end
-    "#,
-    )
-    .exec()?;
-
-    let a = Cell::new(1);
-    let b = Cell::new(1);
-
-    let okay: Function = lua.globals().get("okay")?;
-    let bad: Function = lua.globals().get("bad")?;
-
-    lua.scope(|scope| {
-        let au = scope.create_nonstatic_userdata(MyUserData(&a))?;
-        let bu = scope.create_nonstatic_userdata(MyUserData(&b))?;
-        assert!(okay.call::<_, ()>((au.clone(), bu.clone())).is_ok());
-        match bad.call::<_, ()>((au, bu)) {
-            Err(Error::CallbackError { ref cause, .. }) => match *cause.as_ref() {
-                Error::UserDataTypeMismatch => {}
-                ref other => panic!("wrong error type {:?}", other),
-            },
-            Err(other) => panic!("wrong error type {:?}", other),
-            Ok(_) => panic!("incorrectly returned Ok"),
-        }
-        Ok(())
-    })?;
-
-    Ok(())
-}

tests/tests.rs

@@ -1,6 +1,6 @@
 use std::iter::FromIterator;
 use std::panic::catch_unwind;
-use std::sync::Arc;
+use std::rc::Rc;
 use std::{error, f32, f64, fmt};
 
 use mlua::{
@@ -584,22 +584,22 @@ fn test_registry_value() -> Result<()> {
 
 #[test]
 fn test_drop_registry_value() -> Result<()> {
-    struct MyUserdata(Arc<()>);
+    struct MyUserdata(Rc<()>);
 
     impl UserData for MyUserdata {}
 
     let lua = Lua::new();
-    let rc = Arc::new(());
+    let rc = Rc::new(());
 
     let r = lua.create_registry_value(MyUserdata(rc.clone()))?;
-    assert_eq!(Arc::strong_count(&rc), 2);
+    assert_eq!(Rc::strong_count(&rc), 2);
 
     drop(r);
     lua.expire_registry_values();
 
     lua.load(r#"collectgarbage("collect")"#).exec()?;
 
-    assert_eq!(Arc::strong_count(&rc), 1);
+    assert_eq!(Rc::strong_count(&rc), 1);
 
     Ok(())
 }

tests/thread.rs

@@ -1,4 +1,11 @@
+#![allow(unused_imports)]
+
 use std::panic::catch_unwind;
+use std::rc::Rc;
+use std::time::Duration;
+
+use futures_executor::block_on;
+use futures_util::stream::TryStreamExt;
 
 use mlua::{Error, Function, Lua, Result, Thread, ThreadStatus};
 
@@ -93,6 +100,38 @@ fn test_thread() -> Result<()> {
     Ok(())
 }
 
+#[cfg(feature = "async")]
+#[tokio::test]
+async fn test_thread_stream() -> Result<()> {
+    let lua = Lua::new();
+
+    let thread = lua.create_thread(
+        lua.load(
+            r#"
+            function (s)
+                local sum = s
+                for i = 1,10 do
+                    sum = sum + i
+                    coroutine.yield(sum)
+                end
+                return sum
+            end
+            "#,
+        )
+        .eval()?,
+    )?;
+
+    let mut s = thread.into_async::<_, i64>(0);
+    let mut sum = 0;
+    while let Some(n) = s.try_next().await? {
+        sum += n;
+    }
+
+    assert_eq!(sum, 275);
+
+    Ok(())
+}
+
 #[test]
 fn coroutine_from_closure() -> Result<()> {
     let lua = Lua::new();
@@ -128,3 +167,30 @@ fn coroutine_panic() {
         Err(p) => assert!(*p.downcast::<&str>().unwrap() == "test_panic"),
     }
 }
+
+#[cfg(feature = "async")]
+#[tokio::test]
+async fn test_thread_async() -> Result<()> {
+    let lua = Lua::new();
+
+    let cnt = Rc::new(1); // sleep 1 second
+    let cnt2 = cnt.clone();
+    let f = lua.create_async_function(move |_lua, ()| {
+        let cnt3 = cnt2.clone();
+        async move {
+            futures_timer::Delay::new(Duration::from_secs(*cnt3.as_ref())).await;
+            Ok("hello")
+        }
+    })?;
+
+    let mut thread_s = lua.create_thread(f)?.into_async(());
+    let val: String = thread_s.try_next().await?.unwrap_or_default();
+
+    // thread_s is non-resumable and subject to garbage collection
+
+    lua.gc_collect()?;
+    assert_eq!(Rc::strong_count(&cnt), 1);
+    assert_eq!(val, "hello");
+
+    Ok(())
+}

tests/userdata.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::rc::Rc;
 
 use mlua::{
     AnyUserData, ExternalError, Function, Lua, MetaMethod, Result, String, UserData,
@@ -196,22 +196,22 @@ fn test_gc_userdata() -> Result<()> {
 
 #[test]
 fn detroys_userdata() -> Result<()> {
-    struct MyUserdata(Arc<()>);
+    struct MyUserdata(Rc<()>);
 
     impl UserData for MyUserdata {}
 
-    let rc = Arc::new(());
+    let rc = Rc::new(());
 
     let lua = Lua::new();
     lua.globals().set("userdata", MyUserdata(rc.clone()))?;
 
-    assert_eq!(Arc::strong_count(&rc), 2);
+    assert_eq!(Rc::strong_count(&rc), 2);
 
     // should destroy all objects
     let _ = lua.globals().raw_remove("userdata")?;
     lua.gc_collect()?;
 
-    assert_eq!(Arc::strong_count(&rc), 1);
+    assert_eq!(Rc::strong_count(&rc), 1);
 
     Ok(())
 }
@@ -219,6 +219,7 @@ fn detroys_userdata() -> Result<()> {
 #[test]
 fn user_value() -> Result<()> {
     struct MyUserData;
+
     impl UserData for MyUserData {}
 
     let lua = Lua::new();