v0.5.3

call async Rust callback [sum] 3 10
                        time:   [59.338 us 59.729 us 60.097 us]
                        change: [-10.336% -8.6212% -6.8003%] (p = 0.00 < 0.05)
                        Performance has improved.

CHANGELOG.md

@@ -1,3 +1,8 @@
+## v0.5.3
+
+- Fixed bug when returning nil-prefixed multi values from async function (+ test)
+- Performance optimisation for async callbacks (polling)
+
 ## v0.5.2
 
 - Some performance optimisations (callbacks)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mlua"
-version = "0.5.2" # remember to update html_root_url and mlua_derive
+version = "0.5.3" # remember to update html_root_url and mlua_derive
 authors = ["Aleksandr Orlenko <zxteam@pm.me>", "kyren <catherine@chucklefish.org>"]
 edition = "2018"
 repository = "https://github.com/khvzak/mlua"

benches/benchmark.rs

@@ -13,6 +13,7 @@ extern "system" {}
 use criterion::{criterion_group, criterion_main, BatchSize, Criterion};
 use std::time::Duration;
 use tokio::runtime::Runtime;
+use tokio::task;
 
 use mlua::prelude::*;
 
@@ -117,7 +118,10 @@ fn call_sum_callback(c: &mut Criterion) {
 fn call_async_sum_callback(c: &mut Criterion) {
     let lua = Lua::new();
     let callback = lua
-        .create_async_function(|_, (a, b, c): (i64, i64, i64)| async move { Ok(a + b + c) })
+        .create_async_function(|_, (a, b, c): (i64, i64, i64)| async move {
+            task::yield_now().await;
+            Ok(a + b + c)
+        })
         .unwrap();
     lua.globals().set("callback", callback).unwrap();
 

src/lib.rs

@@ -70,7 +70,7 @@
 //! [`serde::Deserialize`]: https://docs.serde.rs/serde/de/trait.Deserialize.html
 
 // mlua types in rustdoc of other crates get linked to here.
-#![doc(html_root_url = "https://docs.rs/mlua/0.5.2")]
+#![doc(html_root_url = "https://docs.rs/mlua/0.5.3")]
 // Deny warnings inside doc tests / examples. When this isn't present, rustdoc doesn't show *any*
 // warnings at all.
 #![doc(test(attr(deny(warnings))))]

src/lua.rs

@@ -1735,17 +1735,19 @@ impl Lua {
 
                 match (*fut).as_mut().poll(&mut ctx) {
                     Poll::Pending => {
-                        check_stack(state, 6)?;
+                        check_stack(state, 1)?;
                         ffi::lua_pushboolean(state, 0);
-                        push_gc_userdata(state, AsyncPollPending)?;
-                        Ok(2)
+                        Ok(1)
                     }
                     Poll::Ready(results) => {
-                        let results = lua.create_sequence_from(results?)?;
-                        check_stack(state, 2)?;
+                        let results = results?;
+                        let nresults = results.len() as Integer;
+                        let results = lua.create_sequence_from(results)?;
+                        check_stack(state, 3)?;
                         ffi::lua_pushboolean(state, 1);
                         lua.push_value(Value::Table(results))?;
-                        Ok(2)
+                        lua.push_value(Value::Integer(nresults))?;
+                        Ok(3)
                     }
                 }
             })
@@ -1772,24 +1774,31 @@ impl Lua {
         env.set("yield", coroutine.get::<_, Function>("yield")?)?;
         env.set(
             "unpack",
-            self.create_function(|_, tbl: Table| {
+            self.create_function(|_, (tbl, len): (Table, Integer)| {
                 Ok(MultiValue::from_vec(
-                    tbl.sequence_values().collect::<Result<Vec<Value>>>()?,
+                    tbl.raw_sequence_values_by_len(Some(len))
+                        .collect::<Result<Vec<Value>>>()?,
                 ))
             })?,
         )?;
+        env.set("pending", unsafe {
+            let _sg = StackGuard::new(self.state);
+            check_stack(self.state, 5)?;
+            push_gc_userdata(self.state, AsyncPollPending)?;
+            self.pop_value()
+        })?;
 
         // We set `poll` variable in the env table to be able to destroy upvalues
         self.load(
             r#"
             poll = get_poll(...)
-            local poll, yield, unpack = poll, yield, unpack
+            local poll, pending, yield, unpack = poll, pending, yield, unpack
             while true do
-                ready, res = poll()
+                local ready, res, nres = poll()
                 if ready then
-                    return unpack(res)
+                    return unpack(res, nres)
                 end
-                yield(res)
+                yield(pending)
             end
             "#,
         )

src/table.rs

@@ -474,9 +474,11 @@ impl<'lua> Table<'lua> {
         }
     }
 
-    #[cfg(feature = "serialize")]
-    pub(crate) fn raw_sequence_values_by_len<V: FromLua<'lua>>(self) -> TableSequence<'lua, V> {
-        let len = self.raw_len();
+    pub(crate) fn raw_sequence_values_by_len<V: FromLua<'lua>>(
+        self,
+        len: Option<Integer>,
+    ) -> TableSequence<'lua, V> {
+        let len = len.unwrap_or_else(|| self.raw_len());
         TableSequence {
             table: self.0,
             index: Some(1),
@@ -641,7 +643,7 @@ impl<'lua> Serialize for Table<'lua> {
         let len = self.raw_len() as usize;
         if len > 0 || self.is_array() {
             let mut seq = serializer.serialize_seq(Some(len))?;
-            for v in self.clone().raw_sequence_values_by_len::<Value>() {
+            for v in self.clone().raw_sequence_values_by_len::<Value>(None) {
                 let v = v.map_err(serde::ser::Error::custom)?;
                 seq.serialize_element(&v)?;
             }

tests/async.rs

@@ -136,6 +136,24 @@ async fn test_async_handle_yield() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn test_async_multi_return_nil() -> Result<()> {
+    let lua = Lua::new();
+    lua.globals().set(
+        "func",
+        lua.create_async_function(|_, _: ()| async { Ok((Option::<String>::None, "error")) })?,
+    )?;
+
+    lua.load(
+        r#"
+        local ok, err = func()
+        assert(err == "error")
+    "#,
+    )
+    .exec_async()
+    .await
+}
+
 #[tokio::test]
 async fn test_async_return_async_closure() -> Result<()> {
     let lua = Lua::new();

tests/serde.rs

@@ -19,7 +19,7 @@ fn test_serialize() -> Result<(), Box<dyn std::error::Error>> {
     #[derive(Serialize)]
     struct MyUserData(i64, String);
 
-    impl UserData for MyUserData {};
+    impl UserData for MyUserData {}
 
     let lua = Lua::new();
     let globals = lua.globals();
@@ -81,7 +81,7 @@ fn test_serialize_in_scope() -> LuaResult<()> {
     #[derive(Serialize, Clone)]
     struct MyUserData(i64, String);
 
-    impl UserData for MyUserData {};
+    impl UserData for MyUserData {}
 
     let lua = Lua::new();
     lua.scope(|scope| {
@@ -112,7 +112,7 @@ fn test_serialize_failure() -> Result<(), Box<dyn std::error::Error>> {
     #[derive(Serialize)]
     struct MyUserData(i64);
 
-    impl UserData for MyUserData {};
+    impl UserData for MyUserData {}
 
     let lua = Lua::new();
 
@@ -148,7 +148,7 @@ fn test_to_value_struct() -> LuaResult<()> {
         name: String,
         key: i64,
         data: Option<bool>,
-    };
+    }
 
     let test = Test {
         name: "alex".to_string(),
@@ -178,7 +178,7 @@ fn test_to_value_enum() -> LuaResult<()> {
         name: String,
         key: i64,
         data: Option<bool>,
-    };
+    }
 
     let test = Test {
         name: "alex".to_string(),

tests/userdata.rs

@@ -25,8 +25,8 @@ fn test_user_data() -> Result<()> {
     struct UserData1(i64);
     struct UserData2(Box<i64>);
 
-    impl UserData for UserData1 {};
-    impl UserData for UserData2 {};
+    impl UserData for UserData1 {}
+    impl UserData for UserData2 {}
 
     let lua = Lua::new();
     let userdata1 = lua.create_userdata(UserData1(1))?;