Allow using async_io::block_on in bevy_tasks (#9626)

# Objective

Fixes #9625

## Solution

Adds `async-io` as an optional dependency of `bevy_tasks`. When enabled,
this causes calls to `futures_lite::future::block_on` to be replaced
with calls to `async_io::block_on`.

---

## Changelog

- Added a new `async-io` feature to `bevy_tasks`. When enabled, this
causes `bevy_tasks` to use `async-io`'s implemention of `block_on`
instead of `futures-lite`'s implementation. You should enable this if
you use `async-io` in your application.

Cargo.toml

@@ -199,6 +199,9 @@ serialize = ["bevy_internal/serialize"]
 # Enables multithreaded parallelism in the engine. Disabling it forces all engine tasks to run on a single thread.
 multi-threaded = ["bevy_internal/multi-threaded"]
 
+# Use async-io's implementation of block_on instead of futures-lite's implementation. This is preferred if your application uses async-io.
+async-io = ["bevy_internal/async-io"]
+
 # Wayland display server support
 wayland = ["bevy_internal/wayland"]
 

crates/bevy_asset/src/processor/mod.rs

@@ -166,7 +166,7 @@ impl AssetProcessor {
             let processor = _processor.clone();
             std::thread::spawn(move || {
                 processor.process_assets();
-                futures_lite::future::block_on(processor.listen_for_source_change_events());
+                bevy_tasks::block_on(processor.listen_for_source_change_events());
             });
         }
     }
@@ -190,7 +190,7 @@ impl AssetProcessor {
         });
         // This must happen _after_ the scope resolves or it will happen "too early"
         // Don't move this into the async scope above! process_assets is a blocking/sync function this is fine
-        futures_lite::future::block_on(self.finish_processing_assets());
+        bevy_tasks::block_on(self.finish_processing_assets());
         let end_time = std::time::Instant::now();
         debug!("Processing finished in {:?}", end_time - start_time);
     }

crates/bevy_internal/Cargo.toml

@@ -63,6 +63,7 @@ shader_format_spirv = ["bevy_render/shader_format_spirv"]
 
 serialize = ["bevy_core/serialize", "bevy_input/serialize", "bevy_time/serialize", "bevy_window/serialize", "bevy_transform/serialize", "bevy_math/serialize", "bevy_scene?/serialize"]
 multi-threaded = ["bevy_asset/multi-threaded", "bevy_ecs/multi-threaded", "bevy_tasks/multi-threaded"]
+async-io = ["bevy_tasks/async-io"]
 
 # Display server protocol support (X11 is enabled by default)
 wayland = ["bevy_winit/wayland"]

crates/bevy_tasks/Cargo.toml

@@ -15,6 +15,7 @@ multi-threaded = []
 futures-lite = "1.4.0"
 async-executor = "1.3.0"
 async-channel = "1.4.2"
+async-io = { version = "1.13.0", optional = true }
 async-task = "4.2.0"
 concurrent-queue = "2.0.0"
 

crates/bevy_tasks/src/lib.rs

@@ -28,13 +28,19 @@ mod thread_executor;
 #[cfg(all(not(target_arch = "wasm32"), feature = "multi-threaded"))]
 pub use thread_executor::{ThreadExecutor, ThreadExecutorTicker};
 
+#[cfg(feature = "async-io")]
+pub use async_io::block_on;
+#[cfg(not(feature = "async-io"))]
+pub use futures_lite::future::block_on;
+
 mod iter;
 pub use iter::ParallelIterator;
 
 #[allow(missing_docs)]
 pub mod prelude {
     #[doc(hidden)]
     pub use crate::{
+        block_on,
         iter::ParallelIterator,
         slice::{ParallelSlice, ParallelSliceMut},
         usages::{AsyncComputeTaskPool, ComputeTaskPool, IoTaskPool},

crates/bevy_tasks/src/task_pool.rs

@@ -9,9 +9,10 @@ use std::{
 
 use async_task::FallibleTask;
 use concurrent_queue::ConcurrentQueue;
-use futures_lite::{future, FutureExt};
+use futures_lite::FutureExt;
 
 use crate::{
+    block_on,
     thread_executor::{ThreadExecutor, ThreadExecutorTicker},
     Task,
 };
@@ -176,7 +177,7 @@ impl TaskPool {
                                             local_executor.tick().await;
                                         }
                                     };
-                                    future::block_on(ex.run(tick_forever.or(shutdown_rx.recv())))
+                                    block_on(ex.run(tick_forever.or(shutdown_rx.recv())))
                                 });
                                 if let Ok(value) = res {
                                     // Use unwrap_err because we expect a Closed error
@@ -379,7 +380,7 @@ impl TaskPool {
         if spawned.is_empty() {
             Vec::new()
         } else {
-            future::block_on(async move {
+            block_on(async move {
                 let get_results = async {
                     let mut results = Vec::with_capacity(spawned.len());
                     while let Ok(task) = spawned.pop() {
@@ -661,7 +662,7 @@ where
     T: 'scope,
 {
     fn drop(&mut self) {
-        future::block_on(async {
+        block_on(async {
             while let Ok(task) = self.spawned.pop() {
                 task.cancel().await;
             }

docs/cargo_features.md

@@ -43,6 +43,7 @@ The default feature set enables most of the expected features of a game engine,
 |feature name|description|
 |-|-|
 |accesskit_unix|Enable AccessKit on Unix backends (currently only works with experimental screen readers and forks.)|
+|async-io|Use async-io's implementation of block_on instead of futures-lite's implementation. This is preferred if your application uses async-io.|
 |basis-universal|Basis Universal compressed texture support|
 |bevy_ci_testing|Enable systems that allow for automated testing on CI|
 |bevy_dynamic_plugin|Plugin for dynamic loading (using [libloading](https://crates.io/crates/libloading))|

examples/async_tasks/async_compute.rs

@@ -3,7 +3,7 @@
 
 use bevy::{
     prelude::*,
-    tasks::{AsyncComputeTaskPool, Task},
+    tasks::{block_on, AsyncComputeTaskPool, Task},
 };
 use futures_lite::future;
 use rand::Rng;
@@ -88,7 +88,7 @@ fn handle_tasks(
     box_material_handle: Res<BoxMaterialHandle>,
 ) {
     for (entity, mut task) in &mut transform_tasks {
-        if let Some(transform) = future::block_on(future::poll_once(&mut task.0)) {
+        if let Some(transform) = block_on(future::poll_once(&mut task.0)) {
             // Add our new PbrBundle of components to our tagged entity
             commands.entity(entity).insert(PbrBundle {
                 mesh: box_mesh_handle.clone(),