79 lines
2.0 KiB
Rust
79 lines
2.0 KiB
Rust
// Copied from tower/src/semaphore.rs
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// When/if tower-batch is upstreamed, delete this file
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// and use the common tower semaphore implementation
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pub(crate) use self::sync::OwnedSemaphorePermit as Permit;
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use futures_core::ready;
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use std::{
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fmt,
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future::Future,
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mem,
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pin::Pin,
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sync::Arc,
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task::{Context, Poll},
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};
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use tokio::sync;
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#[derive(Debug)]
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pub(crate) struct Semaphore {
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semaphore: Arc<sync::Semaphore>,
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state: State,
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}
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enum State {
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Waiting(Pin<Box<dyn Future<Output = Permit> + Send + Sync + 'static>>),
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Ready(Permit),
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Empty,
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}
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impl Semaphore {
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pub(crate) fn new(permits: usize) -> Self {
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Self {
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semaphore: Arc::new(sync::Semaphore::new(permits)),
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state: State::Empty,
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}
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}
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pub(crate) fn poll_acquire(&mut self, cx: &mut Context<'_>) -> Poll<()> {
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loop {
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self.state = match self.state {
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State::Ready(_) => return Poll::Ready(()),
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State::Waiting(ref mut fut) => {
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let permit = ready!(Pin::new(fut).poll(cx));
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State::Ready(permit)
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}
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State::Empty => State::Waiting(Box::pin(self.semaphore.clone().acquire_owned())),
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};
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}
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}
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pub(crate) fn take_permit(&mut self) -> Option<Permit> {
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if let State::Ready(permit) = mem::replace(&mut self.state, State::Empty) {
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return Some(permit);
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}
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None
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}
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}
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impl Clone for Semaphore {
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fn clone(&self) -> Self {
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Self {
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semaphore: self.semaphore.clone(),
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state: State::Empty,
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}
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}
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}
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impl fmt::Debug for State {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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match self {
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State::Waiting(_) => f
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.debug_tuple("State::Waiting")
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.field(&format_args!("..."))
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.finish(),
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State::Ready(ref r) => f.debug_tuple("State::Ready").field(&r).finish(),
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State::Empty => f.debug_tuple("State::Empty").finish(),
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}
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}
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}
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