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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/git/checkouts/tokio-377c595163f99a10/dfe252d/tokio/src/runtime/task/harness.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>harness.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../../normalize.css"><link rel="stylesheet" href="../../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../../ayu.css" disabled><link rel="stylesheet" href="../../../../dark.css" disabled><link rel="stylesheet" href="../../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../../storage.js"></script><script defer src="../../../../source-script.js"></script><script defer src="../../../../source-files.js"></script><script defer src="../../../../main.js"></script><noscript><link rel="stylesheet" href="../../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../../tokio/index.html"><img class="rust-logo" src="../../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span>
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</pre><pre class="rust"><code><span class="kw">use </span><span class="kw">crate</span>::future::Future;
<span class="kw">use </span><span class="kw">crate</span>::runtime::task::core::{Cell, Core, Header, Trailer};
<span class="kw">use </span><span class="kw">crate</span>::runtime::task::state::{Snapshot, State};
<span class="kw">use </span><span class="kw">crate</span>::runtime::task::waker::waker_ref;
<span class="kw">use </span><span class="kw">crate</span>::runtime::task::{JoinError, Notified, RawTask, Schedule, Task};
<span class="kw">use </span>std::mem;
<span class="kw">use </span>std::mem::ManuallyDrop;
<span class="kw">use </span>std::panic;
<span class="kw">use </span>std::ptr::NonNull;
<span class="kw">use </span>std::task::{Context, Poll, Waker};
<span class="doccomment">/// Typed raw task handle.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>Harness&lt;T: Future, S: <span class="lifetime">&#39;static</span>&gt; {
cell: NonNull&lt;Cell&lt;T, S&gt;&gt;,
}
<span class="kw">impl</span>&lt;T, S&gt; Harness&lt;T, S&gt;
<span class="kw">where
</span>T: Future,
S: <span class="lifetime">&#39;static</span>,
{
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>from_raw(ptr: NonNull&lt;Header&gt;) -&gt; Harness&lt;T, S&gt; {
Harness {
cell: ptr.cast::&lt;Cell&lt;T, S&gt;&gt;(),
}
}
<span class="kw">fn </span>header_ptr(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; NonNull&lt;Header&gt; {
<span class="self">self</span>.cell.cast()
}
<span class="kw">fn </span>header(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>Header {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;*</span><span class="self">self</span>.header_ptr().as_ptr() }
}
<span class="kw">fn </span>state(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>State {
<span class="kw-2">&amp;</span><span class="self">self</span>.header().state
}
<span class="kw">fn </span>trailer(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>Trailer {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;</span><span class="self">self</span>.cell.as_ref().trailer }
}
<span class="kw">fn </span>core(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>Core&lt;T, S&gt; {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;</span><span class="self">self</span>.cell.as_ref().core }
}
}
<span class="doccomment">/// Task operations that can be implemented without being generic over the
/// scheduler or task. Only one version of these methods should exist in the
/// final binary.
</span><span class="kw">impl </span>RawTask {
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>drop_reference(<span class="self">self</span>) {
<span class="kw">if </span><span class="self">self</span>.state().ref_dec() {
<span class="self">self</span>.dealloc();
}
}
<span class="doccomment">/// This call consumes a ref-count and notifies the task. This will create a
/// new Notified and submit it if necessary.
///
/// The caller does not need to hold a ref-count besides the one that was
/// passed to this call.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>wake_by_val(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="kw">use </span><span class="kw">super</span>::state::TransitionToNotifiedByVal;
<span class="kw">match </span><span class="self">self</span>.state().transition_to_notified_by_val() {
TransitionToNotifiedByVal::Submit =&gt; {
<span class="comment">// The caller has given us a ref-count, and the transition has
// created a new ref-count, so we now hold two. We turn the new
// ref-count Notified and pass it to the call to `schedule`.
//
// The old ref-count is retained for now to ensure that the task
// is not dropped during the call to `schedule` if the call
// drops the task it was given.
</span><span class="self">self</span>.schedule();
<span class="comment">// Now that we have completed the call to schedule, we can
// release our ref-count.
</span><span class="self">self</span>.drop_reference();
}
TransitionToNotifiedByVal::Dealloc =&gt; {
<span class="self">self</span>.dealloc();
}
TransitionToNotifiedByVal::DoNothing =&gt; {}
}
}
<span class="doccomment">/// This call notifies the task. It will not consume any ref-counts, but the
/// caller should hold a ref-count. This will create a new Notified and
/// submit it if necessary.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>wake_by_ref(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="kw">use </span><span class="kw">super</span>::state::TransitionToNotifiedByRef;
<span class="kw">match </span><span class="self">self</span>.state().transition_to_notified_by_ref() {
TransitionToNotifiedByRef::Submit =&gt; {
<span class="comment">// The transition above incremented the ref-count for a new task
// and the caller also holds a ref-count. The caller&#39;s ref-count
// ensures that the task is not destroyed even if the new task
// is dropped before `schedule` returns.
</span><span class="self">self</span>.schedule();
}
TransitionToNotifiedByRef::DoNothing =&gt; {}
}
}
<span class="doccomment">/// Remotely aborts the task.
///
/// The caller should hold a ref-count, but we do not consume it.
///
/// This is similar to `shutdown` except that it asks the runtime to perform
/// the shutdown. This is necessary to avoid the shutdown happening in the
/// wrong thread for non-Send tasks.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>remote_abort(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="kw">if </span><span class="self">self</span>.state().transition_to_notified_and_cancel() {
<span class="comment">// The transition has created a new ref-count, which we turn into
// a Notified and pass to the task.
//
// Since the caller holds a ref-count, the task cannot be destroyed
// before the call to `schedule` returns even if the call drops the
// `Notified` internally.
</span><span class="self">self</span>.schedule();
}
}
<span class="doccomment">/// Try to set the waker notified when the task is complete. Returns true if
/// the task has already completed. If this call returns false, then the
/// waker will not be notified.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>try_set_join_waker(<span class="kw-2">&amp;</span><span class="self">self</span>, waker: <span class="kw-2">&amp;</span>Waker) -&gt; bool {
can_read_output(<span class="self">self</span>.header(), <span class="self">self</span>.trailer(), waker)
}
}
<span class="kw">impl</span>&lt;T, S&gt; Harness&lt;T, S&gt;
<span class="kw">where
</span>T: Future,
S: Schedule,
{
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>drop_reference(<span class="self">self</span>) {
<span class="kw">if </span><span class="self">self</span>.state().ref_dec() {
<span class="self">self</span>.dealloc();
}
}
<span class="doccomment">/// Polls the inner future. A ref-count is consumed.
///
/// All necessary state checks and transitions are performed.
/// Panics raised while polling the future are handled.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>poll(<span class="self">self</span>) {
<span class="comment">// We pass our ref-count to `poll_inner`.
</span><span class="kw">match </span><span class="self">self</span>.poll_inner() {
PollFuture::Notified =&gt; {
<span class="comment">// The `poll_inner` call has given us two ref-counts back.
// We give one of them to a new task and call `yield_now`.
</span><span class="self">self</span>.core()
.scheduler
.yield_now(Notified(<span class="self">self</span>.get_new_task()));
<span class="comment">// The remaining ref-count is now dropped. We kept the extra
// ref-count until now to ensure that even if the `yield_now`
// call drops the provided task, the task isn&#39;t deallocated
// before after `yield_now` returns.
</span><span class="self">self</span>.drop_reference();
}
PollFuture::Complete =&gt; {
<span class="self">self</span>.complete();
}
PollFuture::Dealloc =&gt; {
<span class="self">self</span>.dealloc();
}
PollFuture::Done =&gt; (),
}
}
<span class="doccomment">/// Polls the task and cancel it if necessary. This takes ownership of a
/// ref-count.
///
/// If the return value is Notified, the caller is given ownership of two
/// ref-counts.
///
/// If the return value is Complete, the caller is given ownership of a
/// single ref-count, which should be passed on to `complete`.
///
/// If the return value is Dealloc, then this call consumed the last
/// ref-count and the caller should call `dealloc`.
///
/// Otherwise the ref-count is consumed and the caller should not access
/// `self` again.
</span><span class="kw">fn </span>poll_inner(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; PollFuture {
<span class="kw">use </span><span class="kw">super</span>::state::{TransitionToIdle, TransitionToRunning};
<span class="kw">match </span><span class="self">self</span>.state().transition_to_running() {
TransitionToRunning::Success =&gt; {
<span class="kw">let </span>header_ptr = <span class="self">self</span>.header_ptr();
<span class="kw">let </span>waker_ref = waker_ref::&lt;T, S&gt;(<span class="kw-2">&amp;</span>header_ptr);
<span class="kw">let </span>cx = Context::from_waker(<span class="kw-2">&amp;</span>waker_ref);
<span class="kw">let </span>res = poll_future(<span class="self">self</span>.core(), cx);
<span class="kw">if </span>res == Poll::Ready(()) {
<span class="comment">// The future completed. Move on to complete the task.
</span><span class="kw">return </span>PollFuture::Complete;
}
<span class="kw">match </span><span class="self">self</span>.state().transition_to_idle() {
TransitionToIdle::Ok =&gt; PollFuture::Done,
TransitionToIdle::OkNotified =&gt; PollFuture::Notified,
TransitionToIdle::OkDealloc =&gt; PollFuture::Dealloc,
TransitionToIdle::Cancelled =&gt; {
<span class="comment">// The transition to idle failed because the task was
// cancelled during the poll.
</span>cancel_task(<span class="self">self</span>.core());
PollFuture::Complete
}
}
}
TransitionToRunning::Cancelled =&gt; {
cancel_task(<span class="self">self</span>.core());
PollFuture::Complete
}
TransitionToRunning::Failed =&gt; PollFuture::Done,
TransitionToRunning::Dealloc =&gt; PollFuture::Dealloc,
}
}
<span class="doccomment">/// Forcibly shuts down the task.
///
/// Attempt to transition to `Running` in order to forcibly shutdown the
/// task. If the task is currently running or in a state of completion, then
/// there is nothing further to do. When the task completes running, it will
/// notice the `CANCELLED` bit and finalize the task.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>shutdown(<span class="self">self</span>) {
<span class="kw">if </span>!<span class="self">self</span>.state().transition_to_shutdown() {
<span class="comment">// The task is concurrently running. No further work needed.
</span><span class="self">self</span>.drop_reference();
<span class="kw">return</span>;
}
<span class="comment">// By transitioning the lifecycle to `Running`, we have permission to
// drop the future.
</span>cancel_task(<span class="self">self</span>.core());
<span class="self">self</span>.complete();
}
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>dealloc(<span class="self">self</span>) {
<span class="comment">// Release the join waker, if there is one.
</span><span class="self">self</span>.trailer().waker.with_mut(drop);
<span class="comment">// Check causality
</span><span class="self">self</span>.core().stage.with_mut(drop);
<span class="comment">// Safety: The caller of this method just transitioned our ref-count to
// zero, so it is our responsibility to release the allocation.
//
// We don&#39;t hold any references into the allocation at this point, but
// it is possible for another thread to still hold a `&amp;State` into the
// allocation if that other thread has decremented its last ref-count,
// but has not yet returned from the relevant method on `State`.
//
// However, the `State` type consists of just an `AtomicUsize`, and an
// `AtomicUsize` wraps the entirety of its contents in an `UnsafeCell`.
// As explained in the documentation for `UnsafeCell`, such references
// are allowed to be dangling after their last use, even if the
// reference has not yet gone out of scope.
</span><span class="kw">unsafe </span>{
drop(Box::from_raw(<span class="self">self</span>.cell.as_ptr()));
}
}
<span class="comment">// ===== join handle =====
</span><span class="doccomment">/// Read the task output into `dst`.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>try_read_output(<span class="self">self</span>, dst: <span class="kw-2">&amp;mut </span>Poll&lt;<span class="kw">super</span>::Result&lt;T::Output&gt;&gt;, waker: <span class="kw-2">&amp;</span>Waker) {
<span class="kw">if </span>can_read_output(<span class="self">self</span>.header(), <span class="self">self</span>.trailer(), waker) {
<span class="kw-2">*</span>dst = Poll::Ready(<span class="self">self</span>.core().take_output());
}
}
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>drop_join_handle_slow(<span class="self">self</span>) {
<span class="comment">// Try to unset `JOIN_INTEREST`. This must be done as a first step in
// case the task concurrently completed.
</span><span class="kw">if </span><span class="self">self</span>.state().unset_join_interested().is_err() {
<span class="comment">// It is our responsibility to drop the output. This is critical as
// the task output may not be `Send` and as such must remain with
// the scheduler or `JoinHandle`. i.e. if the output remains in the
// task structure until the task is deallocated, it may be dropped
// by a Waker on any arbitrary thread.
//
// Panics are delivered to the user via the `JoinHandle`. Given that
// they are dropping the `JoinHandle`, we assume they are not
// interested in the panic and swallow it.
</span><span class="kw">let _ </span>= panic::catch_unwind(panic::AssertUnwindSafe(|| {
<span class="self">self</span>.core().drop_future_or_output();
}));
}
<span class="comment">// Drop the `JoinHandle` reference, possibly deallocating the task
</span><span class="self">self</span>.drop_reference();
}
<span class="comment">// ====== internal ======
</span><span class="doccomment">/// Completes the task. This method assumes that the state is RUNNING.
</span><span class="kw">fn </span>complete(<span class="self">self</span>) {
<span class="comment">// The future has completed and its output has been written to the task
// stage. We transition from running to complete.
</span><span class="kw">let </span>snapshot = <span class="self">self</span>.state().transition_to_complete();
<span class="comment">// We catch panics here in case dropping the future or waking the
// JoinHandle panics.
</span><span class="kw">let _ </span>= panic::catch_unwind(panic::AssertUnwindSafe(|| {
<span class="kw">if </span>!snapshot.is_join_interested() {
<span class="comment">// The `JoinHandle` is not interested in the output of
// this task. It is our responsibility to drop the
// output.
</span><span class="self">self</span>.core().drop_future_or_output();
} <span class="kw">else if </span>snapshot.is_join_waker_set() {
<span class="comment">// Notify the waker. Reading the waker field is safe per rule 4
// in task/mod.rs, since the JOIN_WAKER bit is set and the call
// to transition_to_complete() above set the COMPLETE bit.
</span><span class="self">self</span>.trailer().wake_join();
}
}));
<span class="comment">// The task has completed execution and will no longer be scheduled.
</span><span class="kw">let </span>num_release = <span class="self">self</span>.release();
<span class="kw">if </span><span class="self">self</span>.state().transition_to_terminal(num_release) {
<span class="self">self</span>.dealloc();
}
}
<span class="doccomment">/// Releases the task from the scheduler. Returns the number of ref-counts
/// that should be decremented.
</span><span class="kw">fn </span>release(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; usize {
<span class="comment">// We don&#39;t actually increment the ref-count here, but the new task is
// never destroyed, so that&#39;s ok.
</span><span class="kw">let </span>me = ManuallyDrop::new(<span class="self">self</span>.get_new_task());
<span class="kw">if let </span><span class="prelude-val">Some</span>(task) = <span class="self">self</span>.core().scheduler.release(<span class="kw-2">&amp;</span>me) {
mem::forget(task);
<span class="number">2
</span>} <span class="kw">else </span>{
<span class="number">1
</span>}
}
<span class="doccomment">/// Creates a new task that holds its own ref-count.
///
/// # Safety
///
/// Any use of `self` after this call must ensure that a ref-count to the
/// task holds the task alive until after the use of `self`. Passing the
/// returned Task to any method on `self` is unsound if dropping the Task
/// could drop `self` before the call on `self` returned.
</span><span class="kw">fn </span>get_new_task(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; Task&lt;S&gt; {
<span class="comment">// safety: The header is at the beginning of the cell, so this cast is
// safe.
</span><span class="kw">unsafe </span>{ Task::from_raw(<span class="self">self</span>.cell.cast()) }
}
}
<span class="kw">fn </span>can_read_output(header: <span class="kw-2">&amp;</span>Header, trailer: <span class="kw-2">&amp;</span>Trailer, waker: <span class="kw-2">&amp;</span>Waker) -&gt; bool {
<span class="comment">// Load a snapshot of the current task state
</span><span class="kw">let </span>snapshot = header.state.load();
<span class="macro">debug_assert!</span>(snapshot.is_join_interested());
<span class="kw">if </span>!snapshot.is_complete() {
<span class="comment">// If the task is not complete, try storing the provided waker in the
// task&#39;s waker field.
</span><span class="kw">let </span>res = <span class="kw">if </span>snapshot.is_join_waker_set() {
<span class="comment">// If JOIN_WAKER is set, then JoinHandle has previously stored a
// waker in the waker field per step (iii) of rule 5 in task/mod.rs.
// Optimization: if the stored waker and the provided waker wake the
// same task, then return without touching the waker field. (Reading
// the waker field below is safe per rule 3 in task/mod.rs.)
</span><span class="kw">if unsafe </span>{ trailer.will_wake(waker) } {
<span class="kw">return </span><span class="bool-val">false</span>;
}
<span class="comment">// Otherwise swap the stored waker with the provided waker by
// following the rule 5 in task/mod.rs.
</span>header
.state
.unset_waker()
.and_then(|snapshot| set_join_waker(header, trailer, waker.clone(), snapshot))
} <span class="kw">else </span>{
<span class="comment">// If JOIN_WAKER is unset, then JoinHandle has mutable access to the
// waker field per rule 2 in task/mod.rs; therefore, skip step (i)
// of rule 5 and try to store the provided waker in the waker field.
</span>set_join_waker(header, trailer, waker.clone(), snapshot)
};
<span class="kw">match </span>res {
<span class="prelude-val">Ok</span>(<span class="kw">_</span>) =&gt; <span class="kw">return </span><span class="bool-val">false</span>,
<span class="prelude-val">Err</span>(snapshot) =&gt; {
<span class="macro">assert!</span>(snapshot.is_complete());
}
}
}
<span class="bool-val">true
</span>}
<span class="kw">fn </span>set_join_waker(
header: <span class="kw-2">&amp;</span>Header,
trailer: <span class="kw-2">&amp;</span>Trailer,
waker: Waker,
snapshot: Snapshot,
) -&gt; <span class="prelude-ty">Result</span>&lt;Snapshot, Snapshot&gt; {
<span class="macro">assert!</span>(snapshot.is_join_interested());
<span class="macro">assert!</span>(!snapshot.is_join_waker_set());
<span class="comment">// Safety: Only the `JoinHandle` may set the `waker` field. When
// `JOIN_INTEREST` is **not** set, nothing else will touch the field.
</span><span class="kw">unsafe </span>{
trailer.set_waker(<span class="prelude-val">Some</span>(waker));
}
<span class="comment">// Update the `JoinWaker` state accordingly
</span><span class="kw">let </span>res = header.state.set_join_waker();
<span class="comment">// If the state could not be updated, then clear the join waker
</span><span class="kw">if </span>res.is_err() {
<span class="kw">unsafe </span>{
trailer.set_waker(<span class="prelude-val">None</span>);
}
}
res
}
<span class="kw">enum </span>PollFuture {
Complete,
Notified,
Done,
Dealloc,
}
<span class="doccomment">/// Cancels the task and store the appropriate error in the stage field.
</span><span class="kw">fn </span>cancel_task&lt;T: Future, S: Schedule&gt;(core: <span class="kw-2">&amp;</span>Core&lt;T, S&gt;) {
<span class="comment">// Drop the future from a panic guard.
</span><span class="kw">let </span>res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
core.drop_future_or_output();
}));
<span class="kw">match </span>res {
<span class="prelude-val">Ok</span>(()) =&gt; {
core.store_output(<span class="prelude-val">Err</span>(JoinError::cancelled(core.task_id)));
}
<span class="prelude-val">Err</span>(panic) =&gt; {
core.store_output(<span class="prelude-val">Err</span>(JoinError::panic(core.task_id, panic)));
}
}
}
<span class="doccomment">/// Polls the future. If the future completes, the output is written to the
/// stage field.
</span><span class="kw">fn </span>poll_future&lt;T: Future, S: Schedule&gt;(core: <span class="kw-2">&amp;</span>Core&lt;T, S&gt;, cx: Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;()&gt; {
<span class="comment">// Poll the future.
</span><span class="kw">let </span>output = panic::catch_unwind(panic::AssertUnwindSafe(|| {
<span class="kw">struct </span>Guard&lt;<span class="lifetime">&#39;a</span>, T: Future, S: Schedule&gt; {
core: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>Core&lt;T, S&gt;,
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>, T: Future, S: Schedule&gt; Drop <span class="kw">for </span>Guard&lt;<span class="lifetime">&#39;a</span>, T, S&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="comment">// If the future panics on poll, we drop it inside the panic
// guard.
</span><span class="self">self</span>.core.drop_future_or_output();
}
}
<span class="kw">let </span>guard = Guard { core };
<span class="kw">let </span>res = guard.core.poll(cx);
mem::forget(guard);
res
}));
<span class="comment">// Prepare output for being placed in the core stage.
</span><span class="kw">let </span>output = <span class="kw">match </span>output {
<span class="prelude-val">Ok</span>(Poll::Pending) =&gt; <span class="kw">return </span>Poll::Pending,
<span class="prelude-val">Ok</span>(Poll::Ready(output)) =&gt; <span class="prelude-val">Ok</span>(output),
<span class="prelude-val">Err</span>(panic) =&gt; {
core.scheduler.unhandled_panic();
<span class="prelude-val">Err</span>(JoinError::panic(core.task_id, panic))
}
};
<span class="comment">// Catch and ignore panics if the future panics on drop.
</span><span class="kw">let </span>res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
core.store_output(output);
}));
<span class="kw">if </span>res.is_err() {
core.scheduler.unhandled_panic();
}
Poll::Ready(())
}
</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>