1 files changed, 275 insertions, 0 deletions
diff --git a/vendor/rayon-core/src/sleep/counters.rs b/vendor/rayon-core/src/sleep/counters.rs
new file mode 100644
index 000000000..29d3b18e2
--- /dev/null
+++ b/vendor/rayon-core/src/sleep/counters.rs
@@ -0,0 +1,275 @@
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+pub(super) struct AtomicCounters {
+    /// Packs together a number of counters. The counters are ordered as
+    /// follows, from least to most significant bits (here, we assuming
+    /// that [`THREADS_BITS`] is equal to 10):
+    ///
+    /// * Bits 0..10: Stores the number of **sleeping threads**
+    /// * Bits 10..20: Stores the number of **inactive threads**
+    /// * Bits 20..: Stores the **job event counter** (JEC)
+    ///
+    /// This uses 10 bits ([`THREADS_BITS`]) to encode the number of threads. Note
+    /// that the total number of bits (and hence the number of bits used for the
+    /// JEC) will depend on whether we are using a 32- or 64-bit architecture.
+    value: AtomicUsize,
+}
+
+#[derive(Copy, Clone)]
+pub(super) struct Counters {
+    word: usize,
+}
+
+/// A value read from the **Jobs Event Counter**.
+/// See the [`README.md`](README.md) for more
+/// coverage of how the jobs event counter works.
+#[derive(Copy, Clone, Debug, PartialEq, PartialOrd)]
+pub(super) struct JobsEventCounter(usize);
+
+impl JobsEventCounter {
+    pub(super) const DUMMY: JobsEventCounter = JobsEventCounter(std::usize::MAX);
+
+    #[inline]
+    pub(super) fn as_usize(self) -> usize {
+        self.0
+    }
+
+    /// The JEC "is sleepy" if the last thread to increment it was in the
+    /// process of becoming sleepy. This is indicated by its value being *even*.
+    /// When new jobs are posted, they check if the JEC is sleepy, and if so
+    /// they incremented it.
+    #[inline]
+    pub(super) fn is_sleepy(self) -> bool {
+        (self.as_usize() & 1) == 0
+    }
+
+    /// The JEC "is active" if the last thread to increment it was posting new
+    /// work. This is indicated by its value being *odd*. When threads get
+    /// sleepy, they will check if the JEC is active, and increment it.
+    #[inline]
+    pub(super) fn is_active(self) -> bool {
+        !self.is_sleepy()
+    }
+}
+
+/// Number of bits used for the thread counters.
+#[cfg(target_pointer_width = "64")]
+const THREADS_BITS: usize = 16;
+
+#[cfg(target_pointer_width = "32")]
+const THREADS_BITS: usize = 8;
+
+/// Bits to shift to select the sleeping threads
+/// (used with `select_bits`).
+const SLEEPING_SHIFT: usize = 0 * THREADS_BITS;
+
+/// Bits to shift to select the inactive threads
+/// (used with `select_bits`).
+const INACTIVE_SHIFT: usize = 1 * THREADS_BITS;
+
+/// Bits to shift to select the JEC
+/// (use JOBS_BITS).
+const JEC_SHIFT: usize = 2 * THREADS_BITS;
+
+/// Max value for the thread counters.
+pub(crate) const THREADS_MAX: usize = (1 << THREADS_BITS) - 1;
+
+/// Constant that can be added to add one sleeping thread.
+const ONE_SLEEPING: usize = 1;
+
+/// Constant that can be added to add one inactive thread.
+/// An inactive thread is either idle, sleepy, or sleeping.
+const ONE_INACTIVE: usize = 1 << INACTIVE_SHIFT;
+
+/// Constant that can be added to add one to the JEC.
+const ONE_JEC: usize = 1 << JEC_SHIFT;
+
+impl AtomicCounters {
+    #[inline]
+    pub(super) fn new() -> AtomicCounters {
+        AtomicCounters {
+            value: AtomicUsize::new(0),
+        }
+    }
+
+    /// Load and return the current value of the various counters.
+    /// This value can then be given to other method which will
+    /// attempt to update the counters via compare-and-swap.
+    #[inline]
+    pub(super) fn load(&self, ordering: Ordering) -> Counters {
+        Counters::new(self.value.load(ordering))
+    }
+
+    #[inline]
+    fn try_exchange(&self, old_value: Counters, new_value: Counters, ordering: Ordering) -> bool {
+        self.value
+            .compare_exchange(old_value.word, new_value.word, ordering, Ordering::Relaxed)
+            .is_ok()
+    }
+
+    /// Adds an inactive thread. This cannot fail.
+    ///
+    /// This should be invoked when a thread enters its idle loop looking
+    /// for work. It is decremented when work is found. Note that it is
+    /// not decremented if the thread transitions from idle to sleepy or sleeping;
+    /// so the number of inactive threads is always greater-than-or-equal
+    /// to the number of sleeping threads.
+    #[inline]
+    pub(super) fn add_inactive_thread(&self) {
+        self.value.fetch_add(ONE_INACTIVE, Ordering::SeqCst);
+    }
+
+    /// Increments the jobs event counter if `increment_when`, when applied to
+    /// the current value, is true. Used to toggle the JEC from even (sleepy) to
+    /// odd (active) or vice versa. Returns the final value of the counters, for
+    /// which `increment_when` is guaranteed to return false.
+    pub(super) fn increment_jobs_event_counter_if(
+        &self,
+        increment_when: impl Fn(JobsEventCounter) -> bool,
+    ) -> Counters {
+        loop {
+            let old_value = self.load(Ordering::SeqCst);
+            if increment_when(old_value.jobs_counter()) {
+                let new_value = old_value.increment_jobs_counter();
+                if self.try_exchange(old_value, new_value, Ordering::SeqCst) {
+                    return new_value;
+                }
+            } else {
+                return old_value;
+            }
+        }
+    }
+
+    /// Subtracts an inactive thread. This cannot fail. It is invoked
+    /// when a thread finds work and hence becomes active. It returns the
+    /// number of sleeping threads to wake up (if any).
+    ///
+    /// See `add_inactive_thread`.
+    #[inline]
+    pub(super) fn sub_inactive_thread(&self) -> usize {
+        let old_value = Counters::new(self.value.fetch_sub(ONE_INACTIVE, Ordering::SeqCst));
+        debug_assert!(
+            old_value.inactive_threads() > 0,
+            "sub_inactive_thread: old_value {:?} has no inactive threads",
+            old_value,
+        );
+        debug_assert!(
+            old_value.sleeping_threads() <= old_value.inactive_threads(),
+            "sub_inactive_thread: old_value {:?} had {} sleeping threads and {} inactive threads",
+            old_value,
+            old_value.sleeping_threads(),
+            old_value.inactive_threads(),
+        );
+
+        // Current heuristic: whenever an inactive thread goes away, if
+        // there are any sleeping threads, wake 'em up.
+        let sleeping_threads = old_value.sleeping_threads();
+        std::cmp::min(sleeping_threads, 2)
+    }
+
+    /// Subtracts a sleeping thread. This cannot fail, but it is only
+    /// safe to do if you you know the number of sleeping threads is
+    /// non-zero (i.e., because you have just awoken a sleeping
+    /// thread).
+    #[inline]
+    pub(super) fn sub_sleeping_thread(&self) {
+        let old_value = Counters::new(self.value.fetch_sub(ONE_SLEEPING, Ordering::SeqCst));
+        debug_assert!(
+            old_value.sleeping_threads() > 0,
+            "sub_sleeping_thread: old_value {:?} had no sleeping threads",
+            old_value,
+        );
+        debug_assert!(
+            old_value.sleeping_threads() <= old_value.inactive_threads(),
+            "sub_sleeping_thread: old_value {:?} had {} sleeping threads and {} inactive threads",
+            old_value,
+            old_value.sleeping_threads(),
+            old_value.inactive_threads(),
+        );
+    }
+
+    #[inline]
+    pub(super) fn try_add_sleeping_thread(&self, old_value: Counters) -> bool {
+        debug_assert!(
+            old_value.inactive_threads() > 0,
+            "try_add_sleeping_thread: old_value {:?} has no inactive threads",
+            old_value,
+        );
+        debug_assert!(
+            old_value.sleeping_threads() < THREADS_MAX,
+            "try_add_sleeping_thread: old_value {:?} has too many sleeping threads",
+            old_value,
+        );
+
+        let mut new_value = old_value;
+        new_value.word += ONE_SLEEPING;
+
+        self.try_exchange(old_value, new_value, Ordering::SeqCst)
+    }
+}
+
+#[inline]
+fn select_thread(word: usize, shift: usize) -> usize {
+    ((word >> shift) as usize) & THREADS_MAX
+}
+
+#[inline]
+fn select_jec(word: usize) -> usize {
+    (word >> JEC_SHIFT) as usize
+}
+
+impl Counters {
+    #[inline]
+    fn new(word: usize) -> Counters {
+        Counters { word }
+    }
+
+    #[inline]
+    fn increment_jobs_counter(self) -> Counters {
+        // We can freely add to JEC because it occupies the most significant bits.
+        // Thus it doesn't overflow into the other counters, just wraps itself.
+        Counters {
+            word: self.word.wrapping_add(ONE_JEC),
+        }
+    }
+
+    #[inline]
+    pub(super) fn jobs_counter(self) -> JobsEventCounter {
+        JobsEventCounter(select_jec(self.word))
+    }
+
+    /// The number of threads that are not actively
+    /// executing work. They may be idle, sleepy, or asleep.
+    #[inline]
+    pub(super) fn inactive_threads(self) -> usize {
+        select_thread(self.word, INACTIVE_SHIFT)
+    }
+
+    #[inline]
+    pub(super) fn awake_but_idle_threads(self) -> usize {
+        debug_assert!(
+            self.sleeping_threads() <= self.inactive_threads(),
+            "sleeping threads: {} > raw idle threads {}",
+            self.sleeping_threads(),
+            self.inactive_threads()
+        );
+        self.inactive_threads() - self.sleeping_threads()
+    }
+
+    #[inline]
+    pub(super) fn sleeping_threads(self) -> usize {
+        select_thread(self.word, SLEEPING_SHIFT)
+    }
+}
+
+impl std::fmt::Debug for Counters {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let word = format!("{:016x}", self.word);
+        fmt.debug_struct("Counters")
+            .field("word", &word)
+            .field("jobs", &self.jobs_counter().0)
+            .field("inactive", &self.inactive_threads())
+            .field("sleeping", &self.sleeping_threads())
+            .finish()
+    }
+}