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block_on.rs
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block_on.rs
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use core::future::Future;
use core::pin::Pin;
use core::ptr;
use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
static VTABLE: RawWakerVTable = RawWakerVTable::new(|_| RawWaker::new(ptr::null(), &VTABLE), |_| {}, |_| {}, |_| {});
/// Run a future to completion using a busy loop.
///
/// This calls `.poll()` on the future in a busy loop, which blocks
/// the current thread at 100% cpu usage until the future is done. The
/// future's `Waker` mechanism is not used.
///
/// You can use this to run multiple futures concurrently with [`join`][crate::join].
///
/// It's suitable for systems with no or limited concurrency and without
/// strict requirements around power consumption. For more complex use
/// cases, prefer using a "real" executor like `embassy-executor`, which
/// supports multiple tasks, and putting the core to sleep when no task
/// needs to do work.
pub fn block_on<F: Future>(mut fut: F) -> F::Output {
// safety: we don't move the future after this line.
let mut fut = unsafe { Pin::new_unchecked(&mut fut) };
let raw_waker = RawWaker::new(ptr::null(), &VTABLE);
let waker = unsafe { Waker::from_raw(raw_waker) };
let mut cx = Context::from_waker(&waker);
loop {
if let Poll::Ready(res) = fut.as_mut().poll(&mut cx) {
return res;
}
}
}
/// Poll a future once.
pub fn poll_once<F: Future>(mut fut: F) -> Poll<F::Output> {
// safety: we don't move the future after this line.
let mut fut = unsafe { Pin::new_unchecked(&mut fut) };
let raw_waker = RawWaker::new(ptr::null(), &VTABLE);
let waker = unsafe { Waker::from_raw(raw_waker) };
let mut cx = Context::from_waker(&waker);
fut.as_mut().poll(&mut cx)
}