pub trait Wake {
// Required method
fn wake(self: Arc<Self>);
// Provided method
fn wake_by_ref(self: &Arc<Self>) { ... }
}Expand description
The implementation of waking a task on an executor.
This trait can be used to create a Waker. An executor can define an
implementation of this trait, and use that to construct a Waker to pass
to the tasks that are executed on that executor.
This trait is a memory-safe and ergonomic alternative to constructing a
RawWaker. It supports the common executor design in which the data used
to wake up a task is stored in an Arc. Some executors (especially
those for embedded systems) cannot use this API, which is why RawWaker
exists as an alternative for those systems.
Examples
A basic block_on function that takes a future and runs it to completion on
the current thread.
Note: This example trades correctness for simplicity. In order to prevent
deadlocks, production-grade implementations will also need to handle
intermediate calls to thread::unpark as well as nested invocations.
use std::future::Future;
use std::sync::Arc;
use std::task::{Context, Poll, Wake};
use std::thread::{self, Thread};
/// A waker that wakes up the current thread when called.
struct ThreadWaker(Thread);
impl Wake for ThreadWaker {
fn wake(self: Arc<Self>) {
self.0.unpark();
}
}
/// Run a future to completion on the current thread.
fn block_on<T>(fut: impl Future<Output = T>) -> T {
// Pin the future so it can be polled.
let mut fut = Box::pin(fut);
// Create a new context to be passed to the future.
let t = thread::current();
let waker = Arc::new(ThreadWaker(t)).into();
let mut cx = Context::from_waker(&waker);
// Run the future to completion.
loop {
match fut.as_mut().poll(&mut cx) {
Poll::Ready(res) => return res,
Poll::Pending => thread::park(),
}
}
}
block_on(async {
println!("Hi from inside a future!");
});