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| </pre><pre class="rust"><code><span class="kw">use </span>futures_core::{ready, Stream}; |
| <span class="kw">use </span>std::fmt; |
| <span class="kw">use </span>std::pin::Pin; |
| <span class="kw">use </span>std::sync::Arc; |
| <span class="kw">use </span>std::task::{Context, Poll}; |
| <span class="kw">use </span>tokio::sync::{AcquireError, OwnedSemaphorePermit, Semaphore, TryAcquireError}; |
| |
| <span class="kw">use </span><span class="kw">super</span>::ReusableBoxFuture; |
| |
| <span class="doccomment">/// A wrapper around [`Semaphore`] that provides a `poll_acquire` method. |
| /// |
| /// [`Semaphore`]: tokio::sync::Semaphore |
| </span><span class="kw">pub struct </span>PollSemaphore { |
| semaphore: Arc<Semaphore>, |
| permit_fut: <span class="prelude-ty">Option</span><( |
| u32, <span class="comment">// The number of permits requested. |
| </span>ReusableBoxFuture<<span class="lifetime">'static</span>, <span class="prelude-ty">Result</span><OwnedSemaphorePermit, AcquireError>>, |
| )>, |
| } |
| |
| <span class="kw">impl </span>PollSemaphore { |
| <span class="doccomment">/// Create a new `PollSemaphore`. |
| </span><span class="kw">pub fn </span>new(semaphore: Arc<Semaphore>) -> <span class="self">Self </span>{ |
| <span class="self">Self </span>{ |
| semaphore, |
| permit_fut: <span class="prelude-val">None</span>, |
| } |
| } |
| |
| <span class="doccomment">/// Closes the semaphore. |
| </span><span class="kw">pub fn </span>close(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="self">self</span>.semaphore.close() |
| } |
| |
| <span class="doccomment">/// Obtain a clone of the inner semaphore. |
| </span><span class="kw">pub fn </span>clone_inner(<span class="kw-2">&</span><span class="self">self</span>) -> Arc<Semaphore> { |
| <span class="self">self</span>.semaphore.clone() |
| } |
| |
| <span class="doccomment">/// Get back the inner semaphore. |
| </span><span class="kw">pub fn </span>into_inner(<span class="self">self</span>) -> Arc<Semaphore> { |
| <span class="self">self</span>.semaphore |
| } |
| |
| <span class="doccomment">/// Poll to acquire a permit from the semaphore. |
| /// |
| /// This can return the following values: |
| /// |
| /// - `Poll::Pending` if a permit is not currently available. |
| /// - `Poll::Ready(Some(permit))` if a permit was acquired. |
| /// - `Poll::Ready(None)` if the semaphore has been closed. |
| /// |
| /// When this method returns `Poll::Pending`, the current task is scheduled |
| /// to receive a wakeup when a permit becomes available, or when the |
| /// semaphore is closed. Note that on multiple calls to `poll_acquire`, only |
| /// the `Waker` from the `Context` passed to the most recent call is |
| /// scheduled to receive a wakeup. |
| </span><span class="kw">pub fn </span>poll_acquire(<span class="kw-2">&mut </span><span class="self">self</span>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="prelude-ty">Option</span><OwnedSemaphorePermit>> { |
| <span class="self">self</span>.poll_acquire_many(cx, <span class="number">1</span>) |
| } |
| |
| <span class="doccomment">/// Poll to acquire many permits from the semaphore. |
| /// |
| /// This can return the following values: |
| /// |
| /// - `Poll::Pending` if a permit is not currently available. |
| /// - `Poll::Ready(Some(permit))` if a permit was acquired. |
| /// - `Poll::Ready(None)` if the semaphore has been closed. |
| /// |
| /// When this method returns `Poll::Pending`, the current task is scheduled |
| /// to receive a wakeup when the permits become available, or when the |
| /// semaphore is closed. Note that on multiple calls to `poll_acquire`, only |
| /// the `Waker` from the `Context` passed to the most recent call is |
| /// scheduled to receive a wakeup. |
| </span><span class="kw">pub fn </span>poll_acquire_many( |
| <span class="kw-2">&mut </span><span class="self">self</span>, |
| cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>, |
| permits: u32, |
| ) -> Poll<<span class="prelude-ty">Option</span><OwnedSemaphorePermit>> { |
| <span class="kw">let </span>permit_future = <span class="kw">match </span><span class="self">self</span>.permit_fut.as_mut() { |
| <span class="prelude-val">Some</span>((prev_permits, fut)) <span class="kw">if </span><span class="kw-2">*</span>prev_permits == permits => fut, |
| <span class="prelude-val">Some</span>((old_permits, fut_box)) => { |
| <span class="comment">// We're requesting a different number of permits, so replace the future |
| // and record the new amount. |
| </span><span class="kw">let </span>fut = Arc::clone(<span class="kw-2">&</span><span class="self">self</span>.semaphore).acquire_many_owned(permits); |
| fut_box.set(fut); |
| <span class="kw-2">*</span>old_permits = permits; |
| fut_box |
| } |
| <span class="prelude-val">None </span>=> { |
| <span class="comment">// avoid allocations completely if we can grab a permit immediately |
| </span><span class="kw">match </span>Arc::clone(<span class="kw-2">&</span><span class="self">self</span>.semaphore).try_acquire_many_owned(permits) { |
| <span class="prelude-val">Ok</span>(permit) => <span class="kw">return </span>Poll::Ready(<span class="prelude-val">Some</span>(permit)), |
| <span class="prelude-val">Err</span>(TryAcquireError::Closed) => <span class="kw">return </span>Poll::Ready(<span class="prelude-val">None</span>), |
| <span class="prelude-val">Err</span>(TryAcquireError::NoPermits) => {} |
| } |
| |
| <span class="kw">let </span>next_fut = Arc::clone(<span class="kw-2">&</span><span class="self">self</span>.semaphore).acquire_many_owned(permits); |
| <span class="kw-2">&mut </span><span class="self">self |
| </span>.permit_fut |
| .get_or_insert((permits, ReusableBoxFuture::new(next_fut))) |
| .<span class="number">1 |
| </span>} |
| }; |
| |
| <span class="kw">let </span>result = <span class="macro">ready!</span>(permit_future.poll(cx)); |
| |
| <span class="comment">// Assume we'll request the same amount of permits in a subsequent call. |
| </span><span class="kw">let </span>next_fut = Arc::clone(<span class="kw-2">&</span><span class="self">self</span>.semaphore).acquire_many_owned(permits); |
| permit_future.set(next_fut); |
| |
| <span class="kw">match </span>result { |
| <span class="prelude-val">Ok</span>(permit) => Poll::Ready(<span class="prelude-val">Some</span>(permit)), |
| <span class="prelude-val">Err</span>(_closed) => { |
| <span class="self">self</span>.permit_fut = <span class="prelude-val">None</span>; |
| Poll::Ready(<span class="prelude-val">None</span>) |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Returns the current number of available permits. |
| /// |
| /// This is equivalent to the [`Semaphore::available_permits`] method on the |
| /// `tokio::sync::Semaphore` type. |
| /// |
| /// [`Semaphore::available_permits`]: tokio::sync::Semaphore::available_permits |
| </span><span class="kw">pub fn </span>available_permits(<span class="kw-2">&</span><span class="self">self</span>) -> usize { |
| <span class="self">self</span>.semaphore.available_permits() |
| } |
| |
| <span class="doccomment">/// Adds `n` new permits to the semaphore. |
| /// |
| /// The maximum number of permits is [`Semaphore::MAX_PERMITS`], and this function |
| /// will panic if the limit is exceeded. |
| /// |
| /// This is equivalent to the [`Semaphore::add_permits`] method on the |
| /// `tokio::sync::Semaphore` type. |
| /// |
| /// [`Semaphore::add_permits`]: tokio::sync::Semaphore::add_permits |
| </span><span class="kw">pub fn </span>add_permits(<span class="kw-2">&</span><span class="self">self</span>, n: usize) { |
| <span class="self">self</span>.semaphore.add_permits(n); |
| } |
| } |
| |
| <span class="kw">impl </span>Stream <span class="kw">for </span>PollSemaphore { |
| <span class="kw">type </span>Item = OwnedSemaphorePermit; |
| |
| <span class="kw">fn </span>poll_next(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="prelude-ty">Option</span><OwnedSemaphorePermit>> { |
| Pin::into_inner(<span class="self">self</span>).poll_acquire(cx) |
| } |
| } |
| |
| <span class="kw">impl </span>Clone <span class="kw">for </span>PollSemaphore { |
| <span class="kw">fn </span>clone(<span class="kw-2">&</span><span class="self">self</span>) -> PollSemaphore { |
| PollSemaphore::new(<span class="self">self</span>.clone_inner()) |
| } |
| } |
| |
| <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>PollSemaphore { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| f.debug_struct(<span class="string">"PollSemaphore"</span>) |
| .field(<span class="string">"semaphore"</span>, <span class="kw-2">&</span><span class="self">self</span>.semaphore) |
| .finish() |
| } |
| } |
| |
| <span class="kw">impl </span>AsRef<Semaphore> <span class="kw">for </span>PollSemaphore { |
| <span class="kw">fn </span>as_ref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>Semaphore { |
| <span class="kw-2">&</span><span class="self">self</span>.semaphore |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tokio_util" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
