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use std::cell::Cell;
use std::future::Future;
use std::pin::Pin;
use std::sync::{Mutex, TryLockError};
use std::task::{Context, Poll};
use futures_core::future::FusedFuture;
use futures_intrusive::sync::{SemaphoreAcquireFuture, SemaphoreReleaser};
pub use futures_intrusive::sync::Semaphore;
use crate::{Canceled, Semaphorish};
#[must_use = "must call `run` or `enter` before blocking"]
#[derive(Debug)]
pub struct BlockingPermit<'a> {
releaser: SemaphoreReleaser<'a>,
pub(crate) entered: Cell<bool>
}
#[must_use = "futures do nothing unless awaited or polled"]
#[derive(Debug)]
pub struct BlockingPermitFuture<'a> {
semaphore: &'a Semaphore,
acquire: Option<SemaphoreAcquireFuture<'a>>
}
impl Semaphorish for Semaphore {
fn default_new(permits: usize) -> Self {
Semaphore::new(true, permits)
}
}
impl<'a> BlockingPermitFuture<'a> {
pub fn new(semaphore: &Semaphore) -> BlockingPermitFuture<'_>
{
BlockingPermitFuture {
semaphore,
acquire: None
}
}
pub fn make_sync(self) -> SyncBlockingPermitFuture<'a> {
SyncBlockingPermitFuture {
futr: Mutex::new(self)
}
}
}
impl<'a> Future for BlockingPermitFuture<'a> {
type Output = Result<BlockingPermit<'a>, Canceled>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>)
-> Poll<Self::Output>
{
let this = unsafe { self.get_unchecked_mut() };
let acq = if let Some(ref mut af) = this.acquire {
af
} else {
this.acquire = Some(this.semaphore.acquire(1));
this.acquire.as_mut().unwrap()
};
let acq = unsafe { Pin::new_unchecked(acq) };
match acq.poll(cx) {
Poll::Pending => Poll::Pending,
Poll::Ready(releaser) => Poll::Ready(Ok(BlockingPermit {
releaser,
entered: Cell::new(false)
})),
}
}
}
impl<'a> FusedFuture for BlockingPermitFuture<'a> {
fn is_terminated(&self) -> bool {
if let Some(ref ff) = self.acquire {
ff.is_terminated()
} else {
false
}
}
}
#[must_use = "futures do nothing unless awaited or polled"]
#[derive(Debug)]
pub struct SyncBlockingPermitFuture<'a> {
futr: Mutex<BlockingPermitFuture<'a>>
}
impl<'a> SyncBlockingPermitFuture<'a> {
pub fn new(semaphore: &'a Semaphore) -> SyncBlockingPermitFuture<'a>
{
SyncBlockingPermitFuture {
futr: Mutex::new(BlockingPermitFuture::new(semaphore))
}
}
}
impl<'a> Future for SyncBlockingPermitFuture<'a> {
type Output = Result<BlockingPermit<'a>, Canceled>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>)
-> Poll<Self::Output>
{
match self.futr.try_lock() {
Ok(mut guard) => {
let futr = unsafe { Pin::new_unchecked(&mut *guard) };
futr.poll(cx)
}
Err(TryLockError::Poisoned(_)) => Poll::Ready(Err(Canceled)),
Err(TryLockError::WouldBlock) => {
cx.waker().wake_by_ref();
Poll::Pending
}
}
}
}