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| </pre><pre class="rust"><code><span class="doccomment">//! Thread-local context used in select. |
| |
| </span><span class="kw">use </span>std::cell::Cell; |
| <span class="kw">use </span>std::ptr; |
| <span class="kw">use </span>std::sync::atomic::{AtomicPtr, AtomicUsize, Ordering}; |
| <span class="kw">use </span>std::sync::Arc; |
| <span class="kw">use </span>std::thread::{<span class="self">self</span>, Thread, ThreadId}; |
| <span class="kw">use </span>std::time::Instant; |
| |
| <span class="kw">use </span>crossbeam_utils::Backoff; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::select::Selected; |
| |
| <span class="doccomment">/// Thread-local context used in select. |
| </span><span class="comment">// This is a private API that is used by the select macro. |
| </span><span class="attribute">#[derive(Debug, Clone)] |
| </span><span class="kw">pub struct </span>Context { |
| inner: Arc<Inner>, |
| } |
| |
| <span class="doccomment">/// Inner representation of `Context`. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">struct </span>Inner { |
| <span class="doccomment">/// Selected operation. |
| </span>select: AtomicUsize, |
| |
| <span class="doccomment">/// A slot into which another thread may store a pointer to its `Packet`. |
| </span>packet: AtomicPtr<()>, |
| |
| <span class="doccomment">/// Thread handle. |
| </span>thread: Thread, |
| |
| <span class="doccomment">/// Thread id. |
| </span>thread_id: ThreadId, |
| } |
| |
| <span class="kw">impl </span>Context { |
| <span class="doccomment">/// Creates a new context for the duration of the closure. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>with<F, R>(f: F) -> R |
| <span class="kw">where |
| </span>F: FnOnce(<span class="kw-2">&</span>Context) -> R, |
| { |
| <span class="macro">thread_local! </span>{ |
| <span class="doccomment">/// Cached thread-local context. |
| </span><span class="kw">static </span>CONTEXT: Cell<<span class="prelude-ty">Option</span><Context>> = Cell::new(<span class="prelude-val">Some</span>(Context::new())); |
| } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="prelude-val">Some</span>(f); |
| <span class="kw">let </span><span class="kw-2">mut </span>f = |cx: <span class="kw-2">&</span>Context| -> R { |
| <span class="kw">let </span>f = f.take().unwrap(); |
| f(cx) |
| }; |
| |
| CONTEXT |
| .try_with(|cell| <span class="kw">match </span>cell.take() { |
| <span class="prelude-val">None </span>=> f(<span class="kw-2">&</span>Context::new()), |
| <span class="prelude-val">Some</span>(cx) => { |
| cx.reset(); |
| <span class="kw">let </span>res = f(<span class="kw-2">&</span>cx); |
| cell.set(<span class="prelude-val">Some</span>(cx)); |
| res |
| } |
| }) |
| .unwrap_or_else(|<span class="kw">_</span>| f(<span class="kw-2">&</span>Context::new())) |
| } |
| |
| <span class="doccomment">/// Creates a new `Context`. |
| </span><span class="attribute">#[cold] |
| </span><span class="kw">fn </span>new() -> Context { |
| Context { |
| inner: Arc::new(Inner { |
| select: AtomicUsize::new(Selected::Waiting.into()), |
| packet: AtomicPtr::new(ptr::null_mut()), |
| thread: thread::current(), |
| thread_id: thread::current().id(), |
| }), |
| } |
| } |
| |
| <span class="doccomment">/// Resets `select` and `packet`. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>reset(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="self">self</span>.inner |
| .select |
| .store(Selected::Waiting.into(), Ordering::Release); |
| <span class="self">self</span>.inner.packet.store(ptr::null_mut(), Ordering::Release); |
| } |
| |
| <span class="doccomment">/// Attempts to select an operation. |
| /// |
| /// On failure, the previously selected operation is returned. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>try_select(<span class="kw-2">&</span><span class="self">self</span>, select: Selected) -> <span class="prelude-ty">Result</span><(), Selected> { |
| <span class="self">self</span>.inner |
| .select |
| .compare_exchange( |
| Selected::Waiting.into(), |
| select.into(), |
| Ordering::AcqRel, |
| Ordering::Acquire, |
| ) |
| .map(|<span class="kw">_</span>| ()) |
| .map_err(|e| e.into()) |
| } |
| |
| <span class="doccomment">/// Returns the selected operation. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>selected(<span class="kw-2">&</span><span class="self">self</span>) -> Selected { |
| Selected::from(<span class="self">self</span>.inner.select.load(Ordering::Acquire)) |
| } |
| |
| <span class="doccomment">/// Stores a packet. |
| /// |
| /// This method must be called after `try_select` succeeds and there is a packet to provide. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>store_packet(<span class="kw-2">&</span><span class="self">self</span>, packet: <span class="kw-2">*mut </span>()) { |
| <span class="kw">if </span>!packet.is_null() { |
| <span class="self">self</span>.inner.packet.store(packet, Ordering::Release); |
| } |
| } |
| |
| <span class="doccomment">/// Waits until a packet is provided and returns it. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>wait_packet(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">*mut </span>() { |
| <span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>packet = <span class="self">self</span>.inner.packet.load(Ordering::Acquire); |
| <span class="kw">if </span>!packet.is_null() { |
| <span class="kw">return </span>packet; |
| } |
| backoff.snooze(); |
| } |
| } |
| |
| <span class="doccomment">/// Waits until an operation is selected and returns it. |
| /// |
| /// If the deadline is reached, `Selected::Aborted` will be selected. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>wait_until(<span class="kw-2">&</span><span class="self">self</span>, deadline: <span class="prelude-ty">Option</span><Instant>) -> Selected { |
| <span class="comment">// Spin for a short time, waiting until an operation is selected. |
| </span><span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>sel = Selected::from(<span class="self">self</span>.inner.select.load(Ordering::Acquire)); |
| <span class="kw">if </span>sel != Selected::Waiting { |
| <span class="kw">return </span>sel; |
| } |
| |
| <span class="kw">if </span>backoff.is_completed() { |
| <span class="kw">break</span>; |
| } <span class="kw">else </span>{ |
| backoff.snooze(); |
| } |
| } |
| |
| <span class="kw">loop </span>{ |
| <span class="comment">// Check whether an operation has been selected. |
| </span><span class="kw">let </span>sel = Selected::from(<span class="self">self</span>.inner.select.load(Ordering::Acquire)); |
| <span class="kw">if </span>sel != Selected::Waiting { |
| <span class="kw">return </span>sel; |
| } |
| |
| <span class="comment">// If there's a deadline, park the current thread until the deadline is reached. |
| </span><span class="kw">if let </span><span class="prelude-val">Some</span>(end) = deadline { |
| <span class="kw">let </span>now = Instant::now(); |
| |
| <span class="kw">if </span>now < end { |
| thread::park_timeout(end - now); |
| } <span class="kw">else </span>{ |
| <span class="comment">// The deadline has been reached. Try aborting select. |
| </span><span class="kw">return match </span><span class="self">self</span>.try_select(Selected::Aborted) { |
| <span class="prelude-val">Ok</span>(()) => Selected::Aborted, |
| <span class="prelude-val">Err</span>(s) => s, |
| }; |
| } |
| } <span class="kw">else </span>{ |
| thread::park(); |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Unparks the thread this context belongs to. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>unpark(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="self">self</span>.inner.thread.unpark(); |
| } |
| |
| <span class="doccomment">/// Returns the id of the thread this context belongs to. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>thread_id(<span class="kw-2">&</span><span class="self">self</span>) -> ThreadId { |
| <span class="self">self</span>.inner.thread_id |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="crossbeam_channel" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
