switch to multitask

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

Cargo.toml

@@ -30,9 +30,9 @@ default = [
   "futures-lite",
   "kv-log-macro",
   "log",
+  "multitask",
   "num_cpus",
   "pin-project-lite",
-  "smol",
 ]
 docs = ["attributes", "unstable", "default"]
 unstable = [
@@ -57,7 +57,7 @@ alloc = [
   "futures-core/alloc",
   "pin-project-lite",
 ]
-tokio02 = ["smol/tokio02"]
+tokio02 = ["tokio"]
 
 [dependencies]
 async-attributes = { version = "1.1.1", optional = true }
@@ -83,7 +83,7 @@ surf = { version = "1.0.3", optional = true }
 async-io = { version = "0.1.5", optional = true }
 blocking = { version = "0.5.0", optional = true }
 futures-lite = { version = "0.1.8", optional = true }
-smol = { version = "0.1.17", optional = true }
+multitask = { version = "0.2.0", optional = true }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 futures-timer = { version = "3.0.2", optional = true, features = ["wasm-bindgen"] }
@@ -93,6 +93,12 @@ futures-channel = { version = "0.3.4", optional = true }
 [target.'cfg(target_arch = "wasm32")'.dev-dependencies]
 wasm-bindgen-test = "0.3.10"
 
+[dependencies.tokio]
+version = "0.2"
+default-features = false
+features = ["rt-threaded"]
+optional = true
+
 [dev-dependencies]
 femme = "1.3.0"
 rand = "0.7.3"

src/task/builder.rs

@@ -7,7 +7,7 @@ use std::task::{Context, Poll};
 use pin_project_lite::pin_project;
 
 use crate::io;
-use crate::task::{JoinHandle, Task, TaskLocalsWrapper};
+use crate::task::{self, JoinHandle, Task, TaskLocalsWrapper};
 
 /// Task builder that configures the settings of a new task.
 #[derive(Debug, Default)]
@@ -61,9 +61,9 @@ impl Builder {
         });
 
         let task = wrapped.tag.task().clone();
-        let smol_task = smol::Task::spawn(wrapped).into();
+        let handle = task::executor::spawn(wrapped);
 
-        Ok(JoinHandle::new(smol_task, task))
+        Ok(JoinHandle::new(handle, task))
     }
 
     /// Spawns a task locally with the configured settings.
@@ -81,9 +81,9 @@ impl Builder {
         });
 
         let task = wrapped.tag.task().clone();
-        let smol_task = smol::Task::local(wrapped).into();
+        let handle = task::executor::local(wrapped);
 
-        Ok(JoinHandle::new(smol_task, task))
+        Ok(JoinHandle::new(handle, task))
     }
 
     /// Spawns a task locally with the configured settings.
@@ -166,8 +166,8 @@ impl Builder {
             unsafe {
                 TaskLocalsWrapper::set_current(&wrapped.tag, || {
                     let res = if should_run {
-                        // The first call should use run.
-                        smol::run(wrapped)
+                        // The first call should run the executor
+                        task::executor::run(wrapped)
                     } else {
                         futures_lite::future::block_on(wrapped)
                     };

src/task/executor.rs

@@ -0,0 +1,91 @@
+use std::cell::RefCell;
+use std::future::Future;
+use std::task::{Context, Poll};
+
+static GLOBAL_EXECUTOR: once_cell::sync::Lazy<multitask::Executor> = once_cell::sync::Lazy::new(multitask::Executor::new);
+
+struct Executor {
+    local_executor: multitask::LocalExecutor,
+    parker: async_io::parking::Parker,
+}
+
+thread_local! {
+    static EXECUTOR: RefCell<Executor> = RefCell::new({
+        let (parker, unparker) = async_io::parking::pair();
+        let local_executor = multitask::LocalExecutor::new(move || unparker.unpark());
+        Executor { local_executor, parker }
+    });
+}
+
+pub(crate) fn spawn<F, T>(future: F) -> multitask::Task<T>
+where
+    F: Future<Output = T> + Send + 'static,
+    T: Send + 'static,
+{
+    GLOBAL_EXECUTOR.spawn(future)
+}
+
+#[cfg(feature = "unstable")]
+pub(crate) fn local<F, T>(future: F) -> multitask::Task<T>
+where
+    F: Future<Output = T> + 'static,
+    T: 'static,
+{
+    EXECUTOR.with(|executor| executor.borrow().local_executor.spawn(future))
+}
+
+pub(crate) fn run<F, T>(future: F) -> T
+where
+    F: Future<Output = T>,
+{
+    enter(|| EXECUTOR.with(|executor| {
+        let executor = executor.borrow();
+        let unparker = executor.parker.unparker();
+        let global_ticker = GLOBAL_EXECUTOR.ticker(move || unparker.unpark());
+        let unparker = executor.parker.unparker();
+        let waker = async_task::waker_fn(move || unparker.unpark());
+        let cx = &mut Context::from_waker(&waker);
+        pin_utils::pin_mut!(future);
+        loop {
+            if let Poll::Ready(res) = future.as_mut().poll(cx) {
+                return res;
+            }
+            if let Ok(false) = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| executor.local_executor.tick() || global_ticker.tick())) {
+                executor.parker.park();
+            }
+        }
+    }))
+}
+
+/// Enters the tokio context if the `tokio` feature is enabled.
+fn enter<T>(f: impl FnOnce() -> T) -> T {
+    #[cfg(not(feature = "tokio02"))]
+    return f();
+
+    #[cfg(feature = "tokio02")]
+    {
+        use std::cell::Cell;
+        use tokio::runtime::Runtime;
+
+        thread_local! {
+            /// The level of nested `enter` calls we are in, to ensure that the outermost always
+            /// has a runtime spawned.
+            static NESTING: Cell<usize> = Cell::new(0);
+        }
+
+        /// The global tokio runtime.
+        static RT: once_cell::sync::Lazy<Runtime> = once_cell::sync::Lazy::new(|| Runtime::new().expect("cannot initialize tokio"));
+
+        NESTING.with(|nesting| {
+            let res = if nesting.get() == 0 {
+                nesting.replace(1);
+                RT.enter(f)
+            } else {
+                nesting.replace(nesting.get() + 1);
+                f()
+            };
+            nesting.replace(nesting.get() - 1);
+            res
+        })
+    }
+}

src/task/join_handle.rs

@@ -18,7 +18,7 @@ pub struct JoinHandle<T> {
 }
 
 #[cfg(not(target_os = "unknown"))]
-type InnerHandle<T> = async_task::JoinHandle<T, ()>;
+type InnerHandle<T> = multitask::Task<T>;
 #[cfg(target_arch = "wasm32")]
 type InnerHandle<T> = futures_channel::oneshot::Receiver<T>;
 
@@ -54,8 +54,7 @@ impl<T> JoinHandle<T> {
     #[cfg(not(target_os = "unknown"))]
     pub async fn cancel(mut self) -> Option<T> {
         let handle = self.handle.take().unwrap();
-        handle.cancel();
-        handle.await
+        handle.cancel().await
     }
 
     /// Cancel this task.
@@ -67,15 +66,19 @@ impl<T> JoinHandle<T> {
     }
 }
 
+#[cfg(not(target_os = "unknown"))]
+impl<T> Drop for JoinHandle<T> {
+    fn drop(&mut self) {
+        if let Some(handle) = self.handle.take() {
+            handle.detach();
+        }
+    }
+}
+
 impl<T> Future for JoinHandle<T> {
     type Output = T;
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        match Pin::new(&mut self.handle.as_mut().unwrap()).poll(cx) {
-            Poll::Pending => Poll::Pending,
-            Poll::Ready(output) => {
-                Poll::Ready(output.expect("cannot await the result of a panicked task"))
-            }
-        }
+        Pin::new(&mut self.handle.as_mut().unwrap()).poll(cx)
     }
 }

src/task/mod.rs

@@ -148,6 +148,8 @@ cfg_default! {
     mod block_on;
     mod builder;
     mod current;
+    #[cfg(not(target_os = "unknown"))]
+    mod executor;
     mod join_handle;
     mod sleep;
     #[cfg(not(target_os = "unknown"))]