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-rw-r--r--vendor/crossbeam-utils/src/backoff.rs287
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diff --git a/vendor/crossbeam-utils/src/backoff.rs b/vendor/crossbeam-utils/src/backoff.rs
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--- a/vendor/crossbeam-utils/src/backoff.rs
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-use crate::primitive::hint;
-use core::cell::Cell;
-use core::fmt;
-
-const SPIN_LIMIT: u32 = 6;
-const YIELD_LIMIT: u32 = 10;
-
-/// Performs exponential backoff in spin loops.
-///
-/// Backing off in spin loops reduces contention and improves overall performance.
-///
-/// This primitive can execute *YIELD* and *PAUSE* instructions, yield the current thread to the OS
-/// scheduler, and tell when is a good time to block the thread using a different synchronization
-/// mechanism. Each step of the back off procedure takes roughly twice as long as the previous
-/// step.
-///
-/// # Examples
-///
-/// Backing off in a lock-free loop:
-///
-/// ```
-/// use crossbeam_utils::Backoff;
-/// use std::sync::atomic::AtomicUsize;
-/// use std::sync::atomic::Ordering::SeqCst;
-///
-/// fn fetch_mul(a: &AtomicUsize, b: usize) -> usize {
-/// let backoff = Backoff::new();
-/// loop {
-/// let val = a.load(SeqCst);
-/// if a.compare_exchange(val, val.wrapping_mul(b), SeqCst, SeqCst).is_ok() {
-/// return val;
-/// }
-/// backoff.spin();
-/// }
-/// }
-/// ```
-///
-/// Waiting for an [`AtomicBool`] to become `true`:
-///
-/// ```
-/// use crossbeam_utils::Backoff;
-/// use std::sync::atomic::AtomicBool;
-/// use std::sync::atomic::Ordering::SeqCst;
-///
-/// fn spin_wait(ready: &AtomicBool) {
-/// let backoff = Backoff::new();
-/// while !ready.load(SeqCst) {
-/// backoff.snooze();
-/// }
-/// }
-/// ```
-///
-/// Waiting for an [`AtomicBool`] to become `true` and parking the thread after a long wait.
-/// Note that whoever sets the atomic variable to `true` must notify the parked thread by calling
-/// [`unpark()`]:
-///
-/// ```
-/// use crossbeam_utils::Backoff;
-/// use std::sync::atomic::AtomicBool;
-/// use std::sync::atomic::Ordering::SeqCst;
-/// use std::thread;
-///
-/// fn blocking_wait(ready: &AtomicBool) {
-/// let backoff = Backoff::new();
-/// while !ready.load(SeqCst) {
-/// if backoff.is_completed() {
-/// thread::park();
-/// } else {
-/// backoff.snooze();
-/// }
-/// }
-/// }
-/// ```
-///
-/// [`is_completed`]: Backoff::is_completed
-/// [`std::thread::park()`]: std::thread::park
-/// [`Condvar`]: std::sync::Condvar
-/// [`AtomicBool`]: std::sync::atomic::AtomicBool
-/// [`unpark()`]: std::thread::Thread::unpark
-pub struct Backoff {
- step: Cell<u32>,
-}
-
-impl Backoff {
- /// Creates a new `Backoff`.
- ///
- /// # Examples
- ///
- /// ```
- /// use crossbeam_utils::Backoff;
- ///
- /// let backoff = Backoff::new();
- /// ```
- #[inline]
- pub fn new() -> Self {
- Backoff { step: Cell::new(0) }
- }
-
- /// Resets the `Backoff`.
- ///
- /// # Examples
- ///
- /// ```
- /// use crossbeam_utils::Backoff;
- ///
- /// let backoff = Backoff::new();
- /// backoff.reset();
- /// ```
- #[inline]
- pub fn reset(&self) {
- self.step.set(0);
- }
-
- /// Backs off in a lock-free loop.
- ///
- /// This method should be used when we need to retry an operation because another thread made
- /// progress.
- ///
- /// The processor may yield using the *YIELD* or *PAUSE* instruction.
- ///
- /// # Examples
- ///
- /// Backing off in a lock-free loop:
- ///
- /// ```
- /// use crossbeam_utils::Backoff;
- /// use std::sync::atomic::AtomicUsize;
- /// use std::sync::atomic::Ordering::SeqCst;
- ///
- /// fn fetch_mul(a: &AtomicUsize, b: usize) -> usize {
- /// let backoff = Backoff::new();
- /// loop {
- /// let val = a.load(SeqCst);
- /// if a.compare_exchange(val, val.wrapping_mul(b), SeqCst, SeqCst).is_ok() {
- /// return val;
- /// }
- /// backoff.spin();
- /// }
- /// }
- ///
- /// let a = AtomicUsize::new(7);
- /// assert_eq!(fetch_mul(&a, 8), 7);
- /// assert_eq!(a.load(SeqCst), 56);
- /// ```
- #[inline]
- pub fn spin(&self) {
- for _ in 0..1 << self.step.get().min(SPIN_LIMIT) {
- hint::spin_loop();
- }
-
- if self.step.get() <= SPIN_LIMIT {
- self.step.set(self.step.get() + 1);
- }
- }
-
- /// Backs off in a blocking loop.
- ///
- /// This method should be used when we need to wait for another thread to make progress.
- ///
- /// The processor may yield using the *YIELD* or *PAUSE* instruction and the current thread
- /// may yield by giving up a timeslice to the OS scheduler.
- ///
- /// In `#[no_std]` environments, this method is equivalent to [`spin`].
- ///
- /// If possible, use [`is_completed`] to check when it is advised to stop using backoff and
- /// block the current thread using a different synchronization mechanism instead.
- ///
- /// [`spin`]: Backoff::spin
- /// [`is_completed`]: Backoff::is_completed
- ///
- /// # Examples
- ///
- /// Waiting for an [`AtomicBool`] to become `true`:
- ///
- /// ```
- /// use crossbeam_utils::Backoff;
- /// use std::sync::Arc;
- /// use std::sync::atomic::AtomicBool;
- /// use std::sync::atomic::Ordering::SeqCst;
- /// use std::thread;
- /// use std::time::Duration;
- ///
- /// fn spin_wait(ready: &AtomicBool) {
- /// let backoff = Backoff::new();
- /// while !ready.load(SeqCst) {
- /// backoff.snooze();
- /// }
- /// }
- ///
- /// let ready = Arc::new(AtomicBool::new(false));
- /// let ready2 = ready.clone();
- ///
- /// thread::spawn(move || {
- /// thread::sleep(Duration::from_millis(100));
- /// ready2.store(true, SeqCst);
- /// });
- ///
- /// assert_eq!(ready.load(SeqCst), false);
- /// spin_wait(&ready);
- /// assert_eq!(ready.load(SeqCst), true);
- /// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
- /// ```
- ///
- /// [`AtomicBool`]: std::sync::atomic::AtomicBool
- #[inline]
- pub fn snooze(&self) {
- if self.step.get() <= SPIN_LIMIT {
- for _ in 0..1 << self.step.get() {
- hint::spin_loop();
- }
- } else {
- #[cfg(not(feature = "std"))]
- for _ in 0..1 << self.step.get() {
- hint::spin_loop();
- }
-
- #[cfg(feature = "std")]
- ::std::thread::yield_now();
- }
-
- if self.step.get() <= YIELD_LIMIT {
- self.step.set(self.step.get() + 1);
- }
- }
-
- /// Returns `true` if exponential backoff has completed and blocking the thread is advised.
- ///
- /// # Examples
- ///
- /// Waiting for an [`AtomicBool`] to become `true` and parking the thread after a long wait:
- ///
- /// ```
- /// use crossbeam_utils::Backoff;
- /// use std::sync::Arc;
- /// use std::sync::atomic::AtomicBool;
- /// use std::sync::atomic::Ordering::SeqCst;
- /// use std::thread;
- /// use std::time::Duration;
- ///
- /// fn blocking_wait(ready: &AtomicBool) {
- /// let backoff = Backoff::new();
- /// while !ready.load(SeqCst) {
- /// if backoff.is_completed() {
- /// thread::park();
- /// } else {
- /// backoff.snooze();
- /// }
- /// }
- /// }
- ///
- /// let ready = Arc::new(AtomicBool::new(false));
- /// let ready2 = ready.clone();
- /// let waiter = thread::current();
- ///
- /// thread::spawn(move || {
- /// thread::sleep(Duration::from_millis(100));
- /// ready2.store(true, SeqCst);
- /// waiter.unpark();
- /// });
- ///
- /// assert_eq!(ready.load(SeqCst), false);
- /// blocking_wait(&ready);
- /// assert_eq!(ready.load(SeqCst), true);
- /// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
- /// ```
- ///
- /// [`AtomicBool`]: std::sync::atomic::AtomicBool
- #[inline]
- pub fn is_completed(&self) -> bool {
- self.step.get() > YIELD_LIMIT
- }
-}
-
-impl fmt::Debug for Backoff {
- fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
- f.debug_struct("Backoff")
- .field("step", &self.step)
- .field("is_completed", &self.is_completed())
- .finish()
- }
-}
-
-impl Default for Backoff {
- fn default() -> Backoff {
- Backoff::new()
- }
-}
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