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libasync: pin tasks to memory

This commit is contained in:
Astro 2020-03-31 01:13:01 +02:00
parent 965a00801e
commit 48257e989c
2 changed files with 17 additions and 22 deletions

View File

@ -34,8 +34,13 @@ static VTABLE: RawWakerVTable = {
///
/// This is a singleton
pub struct Executor {
// Entered block_on() already?
in_block_on: RefCell<bool>,
tasks: RefCell<Deque<Task>>,
/// Tasks reside on the heap, so that we just queue pointers. They
/// must also be pinned in memory because our RawWaker is a pointer
/// to their `ready` field.
tasks: RefCell<Deque<Pin<Box<Task>>>>,
}
impl Executor {
@ -97,17 +102,14 @@ impl Executor {
let mut cx = Context::from_waker(&waker);
// this points into a `static` memory so it's already pinned
// println!("run task");
let ready = unsafe {
Pin::new_unchecked(&mut *task.f)
.poll(&mut cx)
.is_ready()
};
// println!("ran task, ready={:?}", r);
if !ready {
// Task is not finished, requeue
self.tasks.borrow_mut().push_back(task);
let ready = task.f.as_mut().poll(&mut cx).is_ready();
if ready {
// Task is finished, do not requeue
continue;
}
}
// Requeue
self.tasks.borrow_mut().push_back(task);
}
// // try to sleep; this will be a no-op if any of the previous tasks generated a SEV or an
@ -118,26 +120,22 @@ impl Executor {
val
}
// NOTE CAREFUL! this method can overlap with `block_on`
// FIXME we want to use `Future<Output = !>` here but the never type (`!`) is unstable; so as a
// workaround we'll "abort" if the task / future terminates (see `Task::new`)
pub fn spawn(&self, f: impl Future + 'static) {
// NOTE(unsafe) only safe as long as `spawn` is never re-entered and this does not overlap
// with operation `(A)` (see `Task::block_on`)
self.tasks.borrow_mut().push_back(Task::new(f));
let task = Box::pin(Task::new(f));
self.tasks.borrow_mut().push_back(task);
}
}
pub struct Task {
ready: AtomicBool,
f: Box<dyn Future<Output = ()>>,
f: Pin<Box<dyn Future<Output = ()>>>,
}
impl Task {
fn new(f: impl Future + 'static) -> Self {
Task {
ready: AtomicBool::new(true),
f: Box::new(async { f.await; }),
f: Box::pin(async { f.await; }),
}
}
}

View File

@ -17,10 +17,7 @@ pub fn block_on<T>(f: impl Future<Output = T>) -> T {
/// Spawns a task onto the executor
///
/// The spawned task will not make any progress until `block_on` is called.
///
/// The future `f` must never terminate. The program will *abort* if `f` (the async code) returns.
/// The right signature here would be `f: impl Future<Output = !>` but that requires nightly
pub fn spawn<T>(f: impl Future<Output = T> + 'static) {
pub fn spawn(f: impl Future + 'static) {
executor::current().spawn(f)
}