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| </pre><pre class="rust"><code><span class="kw">use </span><span class="kw">crate</span>::loom::sync::Mutex; |
| <span class="kw">use </span><span class="kw">crate</span>::sync::watch; |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span><span class="kw">use </span><span class="kw">crate</span>::util::trace; |
| |
| <span class="doccomment">/// A barrier enables multiple tasks to synchronize the beginning of some computation. |
| /// |
| /// ``` |
| /// # #[tokio::main] |
| /// # async fn main() { |
| /// use tokio::sync::Barrier; |
| /// use std::sync::Arc; |
| /// |
| /// let mut handles = Vec::with_capacity(10); |
| /// let barrier = Arc::new(Barrier::new(10)); |
| /// for _ in 0..10 { |
| /// let c = barrier.clone(); |
| /// // The same messages will be printed together. |
| /// // You will NOT see any interleaving. |
| /// handles.push(tokio::spawn(async move { |
| /// println!("before wait"); |
| /// let wait_result = c.wait().await; |
| /// println!("after wait"); |
| /// wait_result |
| /// })); |
| /// } |
| /// |
| /// // Will not resolve until all "after wait" messages have been printed |
| /// let mut num_leaders = 0; |
| /// for handle in handles { |
| /// let wait_result = handle.await.unwrap(); |
| /// if wait_result.is_leader() { |
| /// num_leaders += 1; |
| /// } |
| /// } |
| /// |
| /// // Exactly one barrier will resolve as the "leader" |
| /// assert_eq!(num_leaders, 1); |
| /// # } |
| /// ``` |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>Barrier { |
| state: Mutex<BarrierState>, |
| wait: watch::Receiver<usize>, |
| n: usize, |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span>resource_span: tracing::Span, |
| } |
| |
| <span class="attribute">#[derive(Debug)] |
| </span><span class="kw">struct </span>BarrierState { |
| waker: watch::Sender<usize>, |
| arrived: usize, |
| generation: usize, |
| } |
| |
| <span class="kw">impl </span>Barrier { |
| <span class="doccomment">/// Creates a new barrier that can block a given number of tasks. |
| /// |
| /// A barrier will block `n`-1 tasks which call [`Barrier::wait`] and then wake up all |
| /// tasks at once when the `n`th task calls `wait`. |
| </span><span class="attribute">#[track_caller] |
| </span><span class="kw">pub fn </span>new(<span class="kw-2">mut </span>n: usize) -> Barrier { |
| <span class="kw">let </span>(waker, wait) = <span class="kw">crate</span>::sync::watch::channel(<span class="number">0</span>); |
| |
| <span class="kw">if </span>n == <span class="number">0 </span>{ |
| <span class="comment">// if n is 0, it's not clear what behavior the user wants. |
| // in std::sync::Barrier, an n of 0 exhibits the same behavior as n == 1, where every |
| // .wait() immediately unblocks, so we adopt that here as well. |
| </span>n = <span class="number">1</span>; |
| } |
| |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span><span class="kw">let </span>resource_span = { |
| <span class="kw">let </span>location = std::panic::Location::caller(); |
| <span class="kw">let </span>resource_span = <span class="macro">tracing::trace_span!</span>( |
| <span class="string">"runtime.resource"</span>, |
| concrete_type = <span class="string">"Barrier"</span>, |
| kind = <span class="string">"Sync"</span>, |
| loc.file = location.file(), |
| loc.line = location.line(), |
| loc.col = location.column(), |
| ); |
| |
| resource_span.in_scope(|| { |
| <span class="macro">tracing::trace!</span>( |
| target: <span class="string">"runtime::resource::state_update"</span>, |
| size = n, |
| ); |
| |
| <span class="macro">tracing::trace!</span>( |
| target: <span class="string">"runtime::resource::state_update"</span>, |
| arrived = <span class="number">0</span>, |
| ) |
| }); |
| resource_span |
| }; |
| |
| Barrier { |
| state: Mutex::new(BarrierState { |
| waker, |
| arrived: <span class="number">0</span>, |
| generation: <span class="number">1</span>, |
| }), |
| n, |
| wait, |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span>resource_span, |
| } |
| } |
| |
| <span class="doccomment">/// Does not resolve until all tasks have rendezvoused here. |
| /// |
| /// Barriers are re-usable after all tasks have rendezvoused once, and can |
| /// be used continuously. |
| /// |
| /// A single (arbitrary) future will receive a [`BarrierWaitResult`] that returns `true` from |
| /// [`BarrierWaitResult::is_leader`] when returning from this function, and all other tasks |
| /// will receive a result that will return `false` from `is_leader`. |
| </span><span class="kw">pub async fn </span>wait(<span class="kw-2">&</span><span class="self">self</span>) -> BarrierWaitResult { |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span><span class="kw">return </span>trace::async_op( |
| || <span class="self">self</span>.wait_internal(), |
| <span class="self">self</span>.resource_span.clone(), |
| <span class="string">"Barrier::wait"</span>, |
| <span class="string">"poll"</span>, |
| <span class="bool-val">false</span>, |
| ) |
| .<span class="kw">await</span>; |
| |
| <span class="attribute">#[cfg(any(not(tokio_unstable), not(feature = <span class="string">"tracing"</span>)))] |
| </span><span class="kw">return </span><span class="self">self</span>.wait_internal().<span class="kw">await</span>; |
| } |
| <span class="kw">async fn </span>wait_internal(<span class="kw-2">&</span><span class="self">self</span>) -> BarrierWaitResult { |
| <span class="comment">// NOTE: we are taking a _synchronous_ lock here. |
| // It is okay to do so because the critical section is fast and never yields, so it cannot |
| // deadlock even if another future is concurrently holding the lock. |
| // It is _desirable_ to do so as synchronous Mutexes are, at least in theory, faster than |
| // the asynchronous counter-parts, so we should use them where possible [citation needed]. |
| // NOTE: the extra scope here is so that the compiler doesn't think `state` is held across |
| // a yield point, and thus marks the returned future as !Send. |
| </span><span class="kw">let </span>generation = { |
| <span class="kw">let </span><span class="kw-2">mut </span>state = <span class="self">self</span>.state.lock(); |
| <span class="kw">let </span>generation = state.generation; |
| state.arrived += <span class="number">1</span>; |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span><span class="macro">tracing::trace!</span>( |
| target: <span class="string">"runtime::resource::state_update"</span>, |
| arrived = <span class="number">1</span>, |
| arrived.op = <span class="string">"add"</span>, |
| ); |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span><span class="macro">tracing::trace!</span>( |
| target: <span class="string">"runtime::resource::async_op::state_update"</span>, |
| arrived = <span class="bool-val">true</span>, |
| ); |
| <span class="kw">if </span>state.arrived == <span class="self">self</span>.n { |
| <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">"tracing"</span>))] |
| </span><span class="macro">tracing::trace!</span>( |
| target: <span class="string">"runtime::resource::async_op::state_update"</span>, |
| is_leader = <span class="bool-val">true</span>, |
| ); |
| <span class="comment">// we are the leader for this generation |
| // wake everyone, increment the generation, and return |
| </span>state |
| .waker |
| .send(state.generation) |
| .expect(<span class="string">"there is at least one receiver"</span>); |
| state.arrived = <span class="number">0</span>; |
| state.generation += <span class="number">1</span>; |
| <span class="kw">return </span>BarrierWaitResult(<span class="bool-val">true</span>); |
| } |
| |
| generation |
| }; |
| |
| <span class="comment">// we're going to have to wait for the last of the generation to arrive |
| </span><span class="kw">let </span><span class="kw-2">mut </span>wait = <span class="self">self</span>.wait.clone(); |
| |
| <span class="kw">loop </span>{ |
| <span class="kw">let _ </span>= wait.changed().<span class="kw">await</span>; |
| |
| <span class="comment">// note that the first time through the loop, this _will_ yield a generation |
| // immediately, since we cloned a receiver that has never seen any values. |
| </span><span class="kw">if </span><span class="kw-2">*</span>wait.borrow() >= generation { |
| <span class="kw">break</span>; |
| } |
| } |
| |
| BarrierWaitResult(<span class="bool-val">false</span>) |
| } |
| } |
| |
| <span class="doccomment">/// A `BarrierWaitResult` is returned by `wait` when all tasks in the `Barrier` have rendezvoused. |
| </span><span class="attribute">#[derive(Debug, Clone)] |
| </span><span class="kw">pub struct </span>BarrierWaitResult(bool); |
| |
| <span class="kw">impl </span>BarrierWaitResult { |
| <span class="doccomment">/// Returns `true` if this task from wait is the "leader task". |
| /// |
| /// Only one task will have `true` returned from their result, all other tasks will have |
| /// `false` returned. |
| </span><span class="kw">pub fn </span>is_leader(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.<span class="number">0 |
| </span>} |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tokio" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
