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</pre><pre class="rust"><code><span class="doccomment">//! Code that decides when workers should go to sleep. See README.md
//! for an overview.
</span><span class="kw">use </span><span class="kw">crate</span>::latch::CoreLatch;
<span class="kw">use </span><span class="kw">crate</span>::log::Event::<span class="kw-2">*</span>;
<span class="kw">use </span><span class="kw">crate</span>::log::Logger;
<span class="kw">use </span>crossbeam_utils::CachePadded;
<span class="kw">use </span>std::sync::atomic::Ordering;
<span class="kw">use </span>std::sync::{Condvar, Mutex};
<span class="kw">use </span>std::thread;
<span class="kw">use </span>std::usize;
<span class="kw">mod </span>counters;
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span><span class="self">self</span>::counters::THREADS_MAX;
<span class="kw">use </span><span class="self">self</span>::counters::{AtomicCounters, JobsEventCounter};
<span class="doccomment">/// The `Sleep` struct is embedded into each registry. It governs the waking and sleeping
/// of workers. It has callbacks that are invoked periodically at significant events,
/// such as when workers are looping and looking for work, when latches are set, or when
/// jobs are published, and it either blocks threads or wakes them in response to these
/// events. See the [`README.md`] in this module for more details.
///
/// [`README.md`] README.md
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>Sleep {
logger: Logger,
<span class="doccomment">/// One &quot;sleep state&quot; per worker. Used to track if a worker is sleeping and to have
/// them block.
</span>worker_sleep_states: Vec&lt;CachePadded&lt;WorkerSleepState&gt;&gt;,
counters: AtomicCounters,
}
<span class="doccomment">/// An instance of this struct is created when a thread becomes idle.
/// It is consumed when the thread finds work, and passed by `&amp;mut`
/// reference for operations that preserve the idle state. (In other
/// words, producing one of these structs is evidence the thread is
/// idle.) It tracks state such as how long the thread has been idle.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>IdleState {
<span class="doccomment">/// What is worker index of the idle thread?
</span>worker_index: usize,
<span class="doccomment">/// How many rounds have we been circling without sleeping?
</span>rounds: u32,
<span class="doccomment">/// Once we become sleepy, what was the sleepy counter value?
/// Set to `INVALID_SLEEPY_COUNTER` otherwise.
</span>jobs_counter: JobsEventCounter,
}
<span class="doccomment">/// The &quot;sleep state&quot; for an individual worker.
</span><span class="attribute">#[derive(Default)]
</span><span class="kw">struct </span>WorkerSleepState {
<span class="doccomment">/// Set to true when the worker goes to sleep; set to false when
/// the worker is notified or when it wakes.
</span>is_blocked: Mutex&lt;bool&gt;,
condvar: Condvar,
}
<span class="kw">const </span>ROUNDS_UNTIL_SLEEPY: u32 = <span class="number">32</span>;
<span class="kw">const </span>ROUNDS_UNTIL_SLEEPING: u32 = ROUNDS_UNTIL_SLEEPY + <span class="number">1</span>;
<span class="kw">impl </span>Sleep {
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new(logger: Logger, n_threads: usize) -&gt; Sleep {
<span class="macro">assert!</span>(n_threads &lt;= THREADS_MAX);
Sleep {
logger,
worker_sleep_states: (<span class="number">0</span>..n_threads).map(|<span class="kw">_</span>| Default::default()).collect(),
counters: AtomicCounters::new(),
}
}
<span class="attribute">#[inline]
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>start_looking(<span class="kw-2">&amp;</span><span class="self">self</span>, worker_index: usize, latch: <span class="kw-2">&amp;</span>CoreLatch) -&gt; IdleState {
<span class="self">self</span>.logger.log(|| ThreadIdle {
worker: worker_index,
latch_addr: latch.addr(),
});
<span class="self">self</span>.counters.add_inactive_thread();
IdleState {
worker_index,
rounds: <span class="number">0</span>,
jobs_counter: JobsEventCounter::DUMMY,
}
}
<span class="attribute">#[inline]
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>work_found(<span class="kw-2">&amp;</span><span class="self">self</span>, idle_state: IdleState) {
<span class="self">self</span>.logger.log(|| ThreadFoundWork {
worker: idle_state.worker_index,
yields: idle_state.rounds,
});
<span class="comment">// If we were the last idle thread and other threads are still sleeping,
// then we should wake up another thread.
</span><span class="kw">let </span>threads_to_wake = <span class="self">self</span>.counters.sub_inactive_thread();
<span class="self">self</span>.wake_any_threads(threads_to_wake <span class="kw">as </span>u32);
}
<span class="attribute">#[inline]
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>no_work_found(
<span class="kw-2">&amp;</span><span class="self">self</span>,
idle_state: <span class="kw-2">&amp;mut </span>IdleState,
latch: <span class="kw-2">&amp;</span>CoreLatch,
has_injected_jobs: <span class="kw">impl </span>FnOnce() -&gt; bool,
) {
<span class="kw">if </span>idle_state.rounds &lt; ROUNDS_UNTIL_SLEEPY {
thread::yield_now();
idle_state.rounds += <span class="number">1</span>;
} <span class="kw">else if </span>idle_state.rounds == ROUNDS_UNTIL_SLEEPY {
idle_state.jobs_counter = <span class="self">self</span>.announce_sleepy(idle_state.worker_index);
idle_state.rounds += <span class="number">1</span>;
thread::yield_now();
} <span class="kw">else if </span>idle_state.rounds &lt; ROUNDS_UNTIL_SLEEPING {
idle_state.rounds += <span class="number">1</span>;
thread::yield_now();
} <span class="kw">else </span>{
<span class="macro">debug_assert_eq!</span>(idle_state.rounds, ROUNDS_UNTIL_SLEEPING);
<span class="self">self</span>.sleep(idle_state, latch, has_injected_jobs);
}
}
<span class="attribute">#[cold]
</span><span class="kw">fn </span>announce_sleepy(<span class="kw-2">&amp;</span><span class="self">self</span>, worker_index: usize) -&gt; JobsEventCounter {
<span class="kw">let </span>counters = <span class="self">self
</span>.counters
.increment_jobs_event_counter_if(JobsEventCounter::is_active);
<span class="kw">let </span>jobs_counter = counters.jobs_counter();
<span class="self">self</span>.logger.log(|| ThreadSleepy {
worker: worker_index,
jobs_counter: jobs_counter.as_usize(),
});
jobs_counter
}
<span class="attribute">#[cold]
</span><span class="kw">fn </span>sleep(
<span class="kw-2">&amp;</span><span class="self">self</span>,
idle_state: <span class="kw-2">&amp;mut </span>IdleState,
latch: <span class="kw-2">&amp;</span>CoreLatch,
has_injected_jobs: <span class="kw">impl </span>FnOnce() -&gt; bool,
) {
<span class="kw">let </span>worker_index = idle_state.worker_index;
<span class="kw">if </span>!latch.get_sleepy() {
<span class="self">self</span>.logger.log(|| ThreadSleepInterruptedByLatch {
worker: worker_index,
latch_addr: latch.addr(),
});
<span class="kw">return</span>;
}
<span class="kw">let </span>sleep_state = <span class="kw-2">&amp;</span><span class="self">self</span>.worker_sleep_states[worker_index];
<span class="kw">let </span><span class="kw-2">mut </span>is_blocked = sleep_state.is_blocked.lock().unwrap();
<span class="macro">debug_assert!</span>(!<span class="kw-2">*</span>is_blocked);
<span class="comment">// Our latch was signalled. We should wake back up fully as we
// will have some stuff to do.
</span><span class="kw">if </span>!latch.fall_asleep() {
<span class="self">self</span>.logger.log(|| ThreadSleepInterruptedByLatch {
worker: worker_index,
latch_addr: latch.addr(),
});
idle_state.wake_fully();
<span class="kw">return</span>;
}
<span class="kw">loop </span>{
<span class="kw">let </span>counters = <span class="self">self</span>.counters.load(Ordering::SeqCst);
<span class="comment">// Check if the JEC has changed since we got sleepy.
</span><span class="macro">debug_assert!</span>(idle_state.jobs_counter.is_sleepy());
<span class="kw">if </span>counters.jobs_counter() != idle_state.jobs_counter {
<span class="comment">// JEC has changed, so a new job was posted, but for some reason
// we didn&#39;t see it. We should return to just before the SLEEPY
// state so we can do another search and (if we fail to find
// work) go back to sleep.
</span><span class="self">self</span>.logger.log(|| ThreadSleepInterruptedByJob {
worker: worker_index,
});
idle_state.wake_partly();
latch.wake_up();
<span class="kw">return</span>;
}
<span class="comment">// Otherwise, let&#39;s move from IDLE to SLEEPING.
</span><span class="kw">if </span><span class="self">self</span>.counters.try_add_sleeping_thread(counters) {
<span class="kw">break</span>;
}
}
<span class="comment">// Successfully registered as asleep.
</span><span class="self">self</span>.logger.log(|| ThreadSleeping {
worker: worker_index,
latch_addr: latch.addr(),
});
<span class="comment">// We have one last check for injected jobs to do. This protects against
// deadlock in the very unlikely event that
//
// - an external job is being injected while we are sleepy
// - that job triggers the rollover over the JEC such that we don&#39;t see it
// - we are the last active worker thread
</span>std::sync::atomic::fence(Ordering::SeqCst);
<span class="kw">if </span>has_injected_jobs() {
<span class="comment">// If we see an externally injected job, then we have to &#39;wake
// ourselves up&#39;. (Ordinarily, `sub_sleeping_thread` is invoked by
// the one that wakes us.)
</span><span class="self">self</span>.counters.sub_sleeping_thread();
} <span class="kw">else </span>{
<span class="comment">// If we don&#39;t see an injected job (the normal case), then flag
// ourselves as asleep and wait till we are notified.
//
// (Note that `is_blocked` is held under a mutex and the mutex was
// acquired *before* we incremented the &quot;sleepy counter&quot;. This means
// that whomever is coming to wake us will have to wait until we
// release the mutex in the call to `wait`, so they will see this
// boolean as true.)
</span><span class="kw-2">*</span>is_blocked = <span class="bool-val">true</span>;
<span class="kw">while </span><span class="kw-2">*</span>is_blocked {
is_blocked = sleep_state.condvar.wait(is_blocked).unwrap();
}
}
<span class="comment">// Update other state:
</span>idle_state.wake_fully();
latch.wake_up();
<span class="self">self</span>.logger.log(|| ThreadAwoken {
worker: worker_index,
latch_addr: latch.addr(),
});
}
<span class="doccomment">/// Notify the given thread that it should wake up (if it is
/// sleeping). When this method is invoked, we typically know the
/// thread is asleep, though in rare cases it could have been
/// awoken by (e.g.) new work having been posted.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>notify_worker_latch_is_set(<span class="kw-2">&amp;</span><span class="self">self</span>, target_worker_index: usize) {
<span class="self">self</span>.wake_specific_thread(target_worker_index);
}
<span class="doccomment">/// Signals that `num_jobs` new jobs were injected into the thread
/// pool from outside. This function will ensure that there are
/// threads available to process them, waking threads from sleep
/// if necessary.
///
/// # Parameters
///
/// - `source_worker_index` -- index of the thread that did the
/// push, or `usize::MAX` if this came from outside the thread
/// pool -- it is used only for logging.
/// - `num_jobs` -- lower bound on number of jobs available for stealing.
/// We&#39;ll try to get at least one thread per job.
</span><span class="attribute">#[inline]
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new_injected_jobs(
<span class="kw-2">&amp;</span><span class="self">self</span>,
source_worker_index: usize,
num_jobs: u32,
queue_was_empty: bool,
) {
<span class="comment">// This fence is needed to guarantee that threads
// as they are about to fall asleep, observe any
// new jobs that may have been injected.
</span>std::sync::atomic::fence(Ordering::SeqCst);
<span class="self">self</span>.new_jobs(source_worker_index, num_jobs, queue_was_empty)
}
<span class="doccomment">/// Signals that `num_jobs` new jobs were pushed onto a thread&#39;s
/// local deque. This function will try to ensure that there are
/// threads available to process them, waking threads from sleep
/// if necessary. However, this is not guaranteed: under certain
/// race conditions, the function may fail to wake any new
/// threads; in that case the existing thread should eventually
/// pop the job.
///
/// # Parameters
///
/// - `source_worker_index` -- index of the thread that did the
/// push, or `usize::MAX` if this came from outside the thread
/// pool -- it is used only for logging.
/// - `num_jobs` -- lower bound on number of jobs available for stealing.
/// We&#39;ll try to get at least one thread per job.
</span><span class="attribute">#[inline]
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new_internal_jobs(
<span class="kw-2">&amp;</span><span class="self">self</span>,
source_worker_index: usize,
num_jobs: u32,
queue_was_empty: bool,
) {
<span class="self">self</span>.new_jobs(source_worker_index, num_jobs, queue_was_empty)
}
<span class="doccomment">/// Common helper for `new_injected_jobs` and `new_internal_jobs`.
</span><span class="attribute">#[inline]
</span><span class="kw">fn </span>new_jobs(<span class="kw-2">&amp;</span><span class="self">self</span>, source_worker_index: usize, num_jobs: u32, queue_was_empty: bool) {
<span class="comment">// Read the counters and -- if sleepy workers have announced themselves
// -- announce that there is now work available. The final value of `counters`
// with which we exit the loop thus corresponds to a state when
</span><span class="kw">let </span>counters = <span class="self">self
</span>.counters
.increment_jobs_event_counter_if(JobsEventCounter::is_sleepy);
<span class="kw">let </span>num_awake_but_idle = counters.awake_but_idle_threads();
<span class="kw">let </span>num_sleepers = counters.sleeping_threads();
<span class="self">self</span>.logger.log(|| JobThreadCounts {
worker: source_worker_index,
num_idle: num_awake_but_idle <span class="kw">as </span>u16,
num_sleepers: num_sleepers <span class="kw">as </span>u16,
});
<span class="kw">if </span>num_sleepers == <span class="number">0 </span>{
<span class="comment">// nobody to wake
</span><span class="kw">return</span>;
}
<span class="comment">// Promote from u16 to u32 so we can interoperate with
// num_jobs more easily.
</span><span class="kw">let </span>num_awake_but_idle = num_awake_but_idle <span class="kw">as </span>u32;
<span class="kw">let </span>num_sleepers = num_sleepers <span class="kw">as </span>u32;
<span class="comment">// If the queue is non-empty, then we always wake up a worker
// -- clearly the existing idle jobs aren&#39;t enough. Otherwise,
// check to see if we have enough idle workers.
</span><span class="kw">if </span>!queue_was_empty {
<span class="kw">let </span>num_to_wake = std::cmp::min(num_jobs, num_sleepers);
<span class="self">self</span>.wake_any_threads(num_to_wake);
} <span class="kw">else if </span>num_awake_but_idle &lt; num_jobs {
<span class="kw">let </span>num_to_wake = std::cmp::min(num_jobs - num_awake_but_idle, num_sleepers);
<span class="self">self</span>.wake_any_threads(num_to_wake);
}
}
<span class="attribute">#[cold]
</span><span class="kw">fn </span>wake_any_threads(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw-2">mut </span>num_to_wake: u32) {
<span class="kw">if </span>num_to_wake &gt; <span class="number">0 </span>{
<span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="self">self</span>.worker_sleep_states.len() {
<span class="kw">if </span><span class="self">self</span>.wake_specific_thread(i) {
num_to_wake -= <span class="number">1</span>;
<span class="kw">if </span>num_to_wake == <span class="number">0 </span>{
<span class="kw">return</span>;
}
}
}
}
}
<span class="kw">fn </span>wake_specific_thread(<span class="kw-2">&amp;</span><span class="self">self</span>, index: usize) -&gt; bool {
<span class="kw">let </span>sleep_state = <span class="kw-2">&amp;</span><span class="self">self</span>.worker_sleep_states[index];
<span class="kw">let </span><span class="kw-2">mut </span>is_blocked = sleep_state.is_blocked.lock().unwrap();
<span class="kw">if </span><span class="kw-2">*</span>is_blocked {
<span class="kw-2">*</span>is_blocked = <span class="bool-val">false</span>;
sleep_state.condvar.notify_one();
<span class="comment">// When the thread went to sleep, it will have incremented
// this value. When we wake it, its our job to decrement
// it. We could have the thread do it, but that would
// introduce a delay between when the thread was
// *notified* and when this counter was decremented. That
// might mislead people with new work into thinking that
// there are sleeping threads that they should try to
// wake, when in fact there is nothing left for them to
// do.
</span><span class="self">self</span>.counters.sub_sleeping_thread();
<span class="self">self</span>.logger.log(|| ThreadNotify { worker: index });
<span class="bool-val">true
</span>} <span class="kw">else </span>{
<span class="bool-val">false
</span>}
}
}
<span class="kw">impl </span>IdleState {
<span class="kw">fn </span>wake_fully(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="self">self</span>.rounds = <span class="number">0</span>;
<span class="self">self</span>.jobs_counter = JobsEventCounter::DUMMY;
}
<span class="kw">fn </span>wake_partly(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="self">self</span>.rounds = ROUNDS_UNTIL_SLEEPY;
<span class="self">self</span>.jobs_counter = JobsEventCounter::DUMMY;
}
}
</code></pre></div>
</section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="rayon_core" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html>