Make tokio / async-io optional task execution engines 2

Cargo.toml

@@ -115,6 +115,10 @@ debug_asset_server = ["bevy_internal/debug_asset_server"]
 # Enable animation support, and glTF animation loading
 animation = ["bevy_internal/animation"]
 
+# alternative async executors, defaults to futures-lite
+async-io = ["bevy_internal/async-io"]
+tokio = ["bevy_internal/tokio"]
+
 [dependencies]
 bevy_dylib = { path = "crates/bevy_dylib", version = "0.9.0-dev", default-features = false, optional = true }
 bevy_internal = { path = "crates/bevy_internal", version = "0.9.0-dev", default-features = false }

crates/bevy_asset/Cargo.toml

@@ -12,6 +12,8 @@ keywords = ["bevy"]
 default = []
 filesystem_watcher = ["notify"]
 debug_asset_server = ["filesystem_watcher"]
+async-io = ["bevy_tasks/async-io"]
+tokio = ["bevy_tasks/tokio"]
 
 [dependencies]
 # bevy
@@ -43,6 +45,5 @@ js-sys = "0.3"
 ndk-glue = { version = "0.5" }
 
 [dev-dependencies]
-futures-lite = "1.4.0"
 tempfile = "3.2.0"
 bevy_core = { path = "../bevy_core", version = "0.9.0-dev" }

crates/bevy_asset/src/asset_server.rs

@@ -800,8 +800,7 @@ mod test {
         let path: AssetPath = "file.not-a-real-extension".into();
         let handle = asset_server.get_handle_untyped(path.get_id());
 
-        let err = futures_lite::future::block_on(asset_server.load_async(path.clone(), true))
-            .unwrap_err();
+        let err = bevy_tasks::block_on(asset_server.load_async(path.clone(), true)).unwrap_err();
         assert!(match err {
             AssetServerError::MissingAssetLoader { extensions } => {
                 extensions == ["not-a-real-extension"]
@@ -820,8 +819,7 @@ mod test {
         let path: AssetPath = "an/invalid/path.png".into();
         let handle = asset_server.get_handle_untyped(path.get_id());
 
-        let err = futures_lite::future::block_on(asset_server.load_async(path.clone(), true))
-            .unwrap_err();
+        let err = bevy_tasks::block_on(asset_server.load_async(path.clone(), true)).unwrap_err();
         assert!(matches!(err, AssetServerError::AssetIoError(_)));
 
         assert_eq!(asset_server.get_load_state(handle), LoadState::Failed);
@@ -836,8 +834,7 @@ mod test {
         let path: AssetPath = "fake.fail".into();
         let handle = asset_server.get_handle_untyped(path.get_id());
 
-        let err = futures_lite::future::block_on(asset_server.load_async(path.clone(), true))
-            .unwrap_err();
+        let err = bevy_tasks::block_on(asset_server.load_async(path.clone(), true)).unwrap_err();
         assert!(matches!(err, AssetServerError::AssetLoaderError(_)));
 
         assert_eq!(asset_server.get_load_state(handle), LoadState::Failed);
@@ -860,8 +857,7 @@ mod test {
 
         fn load_asset(path: AssetPath, world: &World) -> HandleUntyped {
             let asset_server = world.resource::<AssetServer>();
-            let id = futures_lite::future::block_on(asset_server.load_async(path.clone(), true))
-                .unwrap();
+            let id = bevy_tasks::block_on(asset_server.load_async(path.clone(), true)).unwrap();
             asset_server.get_handle_untyped(id)
         }
 

crates/bevy_internal/Cargo.toml

@@ -63,6 +63,10 @@ bevy_ci_testing = ["bevy_app/bevy_ci_testing", "bevy_render/ci_limits"]
 # Enable animation support, and glTF animation loading
 animation = ["bevy_animation", "bevy_gltf?/bevy_animation"]
 
+# alternative async executors, defaults to futures-lite
+async-io = ["bevy_tasks/async-io"]
+tokio = ["bevy_tasks/tokio"]
+
 [dependencies]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.9.0-dev" }

crates/bevy_render/Cargo.toml

@@ -59,7 +59,7 @@ once_cell = "1.4.1" # TODO: replace once_cell with std equivalent if/when this l
 downcast-rs = "1.2.0"
 thread_local = "1.1"
 thiserror = "1.0"
-futures-lite = "1.4.0"
+futures-lite = "1.12"
 anyhow = "1.0"
 hex = "0.4.2"
 hexasphere = "7.2"

crates/bevy_tasks/Cargo.toml

@@ -8,8 +8,13 @@ repository = "https://github.com/bevyengine/bevy"
 license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
+[features]
+async-io = ["async-global-executor/async-io"]
+tokio = ["async-global-executor/tokio"]
+
 [dependencies]
-futures-lite = "1.4.0"
+futures-lite = "1.12.0"
+async-global-executor= { version="2.2.0", default-features = false }
 async-executor = "1.3.0"
 async-channel = "1.4.2"
 once_cell = "1.7"

crates/bevy_tasks/src/lib.rs

@@ -23,6 +23,10 @@ pub use usages::{AsyncComputeTaskPool, ComputeTaskPool, IoTaskPool};
 mod iter;
 pub use iter::ParallelIterator;
 
+// re-export block_on so that consumers don't need to explicitly depend on the async engine being used.
+// it uses futures-lite by default, async-io and tokio are optional behind features
+pub use async_global_executor::block_on;
+
 #[allow(missing_docs)]
 pub mod prelude {
     #[doc(hidden)]

crates/bevy_tasks/src/task_pool.rs

@@ -119,7 +119,7 @@ impl TaskPool {
                     .spawn(move || {
                         let shutdown_future = ex.run(shutdown_rx.recv());
                         // Use unwrap_err because we expect a Closed error
-                        future::block_on(shutdown_future).unwrap_err();
+                        crate::block_on(shutdown_future).unwrap_err();
                     })
                     .expect("Failed to spawn thread.")
             })
@@ -269,11 +269,11 @@ impl TaskPool {
             // forward until the tasks that are spawned by this scope() call
             // complete. (If the caller of scope() happens to be a thread in
             // this thread pool, and we only have one thread in the pool, then
-            // simply calling future::block_on(spawned) would deadlock.)
+            // simply calling crate::block_on(spawned) would deadlock.)
             let mut spawned = task_scope_executor.spawn(get_results);
 
             loop {
-                if let Some(result) = future::block_on(future::poll_once(&mut spawned)) {
+                if let Some(result) = crate::block_on(future::poll_once(&mut spawned)) {
                     break result;
                 };
 

docs/cargo_features.md

@@ -44,3 +44,5 @@
 |subpixel_glyph_atlas|Enable this to cache glyphs using subpixel accuracy. This increases texture memory usage as each position requires a separate sprite in the glyph atlas, but provide more accurate character spacing.|
 |bevy_ci_testing|Used for running examples in CI.|
 |debug_asset_server|Enabling this turns on "hot reloading" of built in assets, such as shaders.|
+|tokio|Use tokio as task execution engine.|
+|async-io|Use async-io as task execution engine.|

examples/async_tasks/async_compute.rs

@@ -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) = bevy::tasks::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(),