Module glommio::task

Task abstraction for building executors.

Spawning

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

When a task is run, its future gets polled. If polling does not complete the task, that means it's waiting for another future and needs to go to sleep. When woken up, its schedule function will be invoked, pushing it back into the queue so that it can be run again.

Paired with a task there usually is a JoinHandle that can be used to wait for the task's completion.

Cancellation

Both Task and JoinHandle have methods that cancel the task. When canceled, the task's future will not be polled again and will get dropped instead.

If canceled by the Task instance, the task is destroyed immediately. If canceled by the JoinHandle instance, it will be scheduled one more time and the next attempt to run it will simply destroy it.

The JoinHandle future will then evaluate to None, but only after the task's future is dropped.

Performance

Task construction incurs a single allocation that holds its state, the schedule function, and the future or the result of the future if completed.

The layout of a task is equivalent to 4 usizes followed by the schedule function, and then by a union of the future and its output.

Waking

The handy waker_fn constructor converts any function into a Waker. Every time it is woken, the function gets called:

let waker = glommio::task::waker_fn(|| println!("Wake!"));

// Prints "Wake!" twice.
waker.wake_by_ref();
waker.wake_by_ref();

Structs

JoinHandle	A handle that awaits the result of a task.
Task	A task reference that runs its future.

Functions

waker_fn

Creates a waker from a wake function.