Task abstraction for building executors
Task abstraction for building 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(), or
spawn_unchecked()which return a
Runnableand 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::spawn(future, schedule);
// Push the task into the queue by invoking its schedule function. runnable.schedule();
The
Runnableis used to poll the task's future, and the
Taskis 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
Runnablevanishes and only reappears when its
Wakerwakes the task, thus scheduling it to be run again.
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