Crate async_task_ffi

Task abstraction for building executors.

This is a fork of async-task with additional features useful for ffi based executors.

To spawn a future onto an executor, we first need to allocate it on the heap and keep some state attached to it. The state indicates whether the future is ready for polling, waiting to be woken up, or completed. Such a stateful future is called a task.

All executors have a queue that holds scheduled tasks:

let (sender, receiver) = flume::unbounded();

A task is created using either spawn(), spawn_local(), spawn_unchecked() or their _with variants which return a Runnable and a Task:

// A future that will be spawned.
let future = async { 1 + 2 };

// A function that schedules the task when it gets woken up.
let schedule = move |runnable| sender.send(runnable).unwrap();

// Construct a task.
let (runnable, task) = async_task_ffi::spawn(future, schedule);

// Push the task into the queue by invoking its schedule function.
runnable.schedule();

The Runnable is used to poll the task’s future, and the Task is used to await its output.

Finally, we need a loop that takes scheduled tasks from the queue and runs them:

for runnable in receiver {
    runnable.run();
}

Method run() polls the task’s future once. Then, the Runnable vanishes and only reappears when its Waker wakes the task, thus scheduling it to be run again.

Structs

Runnable

A handle to a runnable task.

Task

A spawned task.

Functions

spawn

Creates a new task.

spawn_local

Creates a new thread-local task.

spawn_local_with

Creates a new thread-local task with associated data.

spawn_unchecked^⚠

Creates a new task without Send, Sync, and 'static bounds.

spawn_unchecked_with^⚠

Creates a new task with associated data and without Send, Sync, and 'static bounds.

spawn_with

Creates a new task with associated data.