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Diffstat (limited to 'vendor/crossbeam-utils/src/sync/parker.rs')
| -rw-r--r-- | vendor/crossbeam-utils/src/sync/parker.rs | 415 |
1 files changed, 0 insertions, 415 deletions
diff --git a/vendor/crossbeam-utils/src/sync/parker.rs b/vendor/crossbeam-utils/src/sync/parker.rs deleted file mode 100644 index 971981d..0000000 --- a/vendor/crossbeam-utils/src/sync/parker.rs +++ /dev/null @@ -1,415 +0,0 @@ -use crate::primitive::sync::atomic::{AtomicUsize, Ordering::SeqCst}; -use crate::primitive::sync::{Arc, Condvar, Mutex}; -use std::fmt; -use std::marker::PhantomData; -use std::time::{Duration, Instant}; - -/// A thread parking primitive. -/// -/// Conceptually, each `Parker` has an associated token which is initially not present: -/// -/// * The [`park`] method blocks the current thread unless or until the token is available, at -/// which point it automatically consumes the token. -/// -/// * The [`park_timeout`] and [`park_deadline`] methods work the same as [`park`], but block for -/// a specified maximum time. -/// -/// * The [`unpark`] method atomically makes the token available if it wasn't already. Because the -/// token is initially absent, [`unpark`] followed by [`park`] will result in the second call -/// returning immediately. -/// -/// In other words, each `Parker` acts a bit like a spinlock that can be locked and unlocked using -/// [`park`] and [`unpark`]. -/// -/// # Examples -/// -/// ``` -/// use std::thread; -/// use std::time::Duration; -/// use crossbeam_utils::sync::Parker; -/// -/// let p = Parker::new(); -/// let u = p.unparker().clone(); -/// -/// // Make the token available. -/// u.unpark(); -/// // Wakes up immediately and consumes the token. -/// p.park(); -/// -/// thread::spawn(move || { -/// thread::sleep(Duration::from_millis(500)); -/// u.unpark(); -/// }); -/// -/// // Wakes up when `u.unpark()` provides the token. -/// p.park(); -/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371 -/// ``` -/// -/// [`park`]: Parker::park -/// [`park_timeout`]: Parker::park_timeout -/// [`park_deadline`]: Parker::park_deadline -/// [`unpark`]: Unparker::unpark -pub struct Parker { - unparker: Unparker, - _marker: PhantomData<*const ()>, -} - -unsafe impl Send for Parker {} - -impl Default for Parker { - fn default() -> Self { - Self { - unparker: Unparker { - inner: Arc::new(Inner { - state: AtomicUsize::new(EMPTY), - lock: Mutex::new(()), - cvar: Condvar::new(), - }), - }, - _marker: PhantomData, - } - } -} - -impl Parker { - /// Creates a new `Parker`. - /// - /// # Examples - /// - /// ``` - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// ``` - /// - pub fn new() -> Parker { - Self::default() - } - - /// Blocks the current thread until the token is made available. - /// - /// # Examples - /// - /// ``` - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// let u = p.unparker().clone(); - /// - /// // Make the token available. - /// u.unpark(); - /// - /// // Wakes up immediately and consumes the token. - /// p.park(); - /// ``` - pub fn park(&self) { - self.unparker.inner.park(None); - } - - /// Blocks the current thread until the token is made available, but only for a limited time. - /// - /// # Examples - /// - /// ``` - /// use std::time::Duration; - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// - /// // Waits for the token to become available, but will not wait longer than 500 ms. - /// p.park_timeout(Duration::from_millis(500)); - /// ``` - pub fn park_timeout(&self, timeout: Duration) { - match Instant::now().checked_add(timeout) { - Some(deadline) => self.park_deadline(deadline), - None => self.park(), - } - } - - /// Blocks the current thread until the token is made available, or until a certain deadline. - /// - /// # Examples - /// - /// ``` - /// use std::time::{Duration, Instant}; - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// let deadline = Instant::now() + Duration::from_millis(500); - /// - /// // Waits for the token to become available, but will not wait longer than 500 ms. - /// p.park_deadline(deadline); - /// ``` - pub fn park_deadline(&self, deadline: Instant) { - self.unparker.inner.park(Some(deadline)) - } - - /// Returns a reference to an associated [`Unparker`]. - /// - /// The returned [`Unparker`] doesn't have to be used by reference - it can also be cloned. - /// - /// # Examples - /// - /// ``` - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// let u = p.unparker().clone(); - /// - /// // Make the token available. - /// u.unpark(); - /// // Wakes up immediately and consumes the token. - /// p.park(); - /// ``` - /// - /// [`park`]: Parker::park - /// [`park_timeout`]: Parker::park_timeout - pub fn unparker(&self) -> &Unparker { - &self.unparker - } - - /// Converts a `Parker` into a raw pointer. - /// - /// # Examples - /// - /// ``` - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// let raw = Parker::into_raw(p); - /// # let _ = unsafe { Parker::from_raw(raw) }; - /// ``` - pub fn into_raw(this: Parker) -> *const () { - Unparker::into_raw(this.unparker) - } - - /// Converts a raw pointer into a `Parker`. - /// - /// # Safety - /// - /// This method is safe to use only with pointers returned by [`Parker::into_raw`]. - /// - /// # Examples - /// - /// ``` - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// let raw = Parker::into_raw(p); - /// let p = unsafe { Parker::from_raw(raw) }; - /// ``` - pub unsafe fn from_raw(ptr: *const ()) -> Parker { - Parker { - unparker: Unparker::from_raw(ptr), - _marker: PhantomData, - } - } -} - -impl fmt::Debug for Parker { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.pad("Parker { .. }") - } -} - -/// Unparks a thread parked by the associated [`Parker`]. -pub struct Unparker { - inner: Arc<Inner>, -} - -unsafe impl Send for Unparker {} -unsafe impl Sync for Unparker {} - -impl Unparker { - /// Atomically makes the token available if it is not already. - /// - /// This method will wake up the thread blocked on [`park`] or [`park_timeout`], if there is - /// any. - /// - /// # Examples - /// - /// ``` - /// use std::thread; - /// use std::time::Duration; - /// use crossbeam_utils::sync::Parker; - /// - /// let p = Parker::new(); - /// let u = p.unparker().clone(); - /// - /// thread::spawn(move || { - /// thread::sleep(Duration::from_millis(500)); - /// u.unpark(); - /// }); - /// - /// // Wakes up when `u.unpark()` provides the token. - /// p.park(); - /// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371 - /// ``` - /// - /// [`park`]: Parker::park - /// [`park_timeout`]: Parker::park_timeout - pub fn unpark(&self) { - self.inner.unpark() - } - - /// Converts an `Unparker` into a raw pointer. - /// - /// # Examples - /// - /// ``` - /// use crossbeam_utils::sync::{Parker, Unparker}; - /// - /// let p = Parker::new(); - /// let u = p.unparker().clone(); - /// let raw = Unparker::into_raw(u); - /// # let _ = unsafe { Unparker::from_raw(raw) }; - /// ``` - pub fn into_raw(this: Unparker) -> *const () { - Arc::into_raw(this.inner).cast::<()>() - } - - /// Converts a raw pointer into an `Unparker`. - /// - /// # Safety - /// - /// This method is safe to use only with pointers returned by [`Unparker::into_raw`]. - /// - /// # Examples - /// - /// ``` - /// use crossbeam_utils::sync::{Parker, Unparker}; - /// - /// let p = Parker::new(); - /// let u = p.unparker().clone(); - /// - /// let raw = Unparker::into_raw(u); - /// let u = unsafe { Unparker::from_raw(raw) }; - /// ``` - pub unsafe fn from_raw(ptr: *const ()) -> Unparker { - Unparker { - inner: Arc::from_raw(ptr.cast::<Inner>()), - } - } -} - -impl fmt::Debug for Unparker { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.pad("Unparker { .. }") - } -} - -impl Clone for Unparker { - fn clone(&self) -> Unparker { - Unparker { - inner: self.inner.clone(), - } - } -} - -const EMPTY: usize = 0; -const PARKED: usize = 1; -const NOTIFIED: usize = 2; - -struct Inner { - state: AtomicUsize, - lock: Mutex<()>, - cvar: Condvar, -} - -impl Inner { - fn park(&self, deadline: Option<Instant>) { - // If we were previously notified then we consume this notification and return quickly. - if self - .state - .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst) - .is_ok() - { - return; - } - - // If the timeout is zero, then there is no need to actually block. - if let Some(deadline) = deadline { - if deadline <= Instant::now() { - return; - } - } - - // Otherwise we need to coordinate going to sleep. - let mut m = self.lock.lock().unwrap(); - - match self.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) { - Ok(_) => {} - // Consume this notification to avoid spurious wakeups in the next park. - Err(NOTIFIED) => { - // We must read `state` here, even though we know it will be `NOTIFIED`. This is - // because `unpark` may have been called again since we read `NOTIFIED` in the - // `compare_exchange` above. We must perform an acquire operation that synchronizes - // with that `unpark` to observe any writes it made before the call to `unpark`. To - // do that we must read from the write it made to `state`. - let old = self.state.swap(EMPTY, SeqCst); - assert_eq!(old, NOTIFIED, "park state changed unexpectedly"); - return; - } - Err(n) => panic!("inconsistent park_timeout state: {}", n), - } - - loop { - // Block the current thread on the conditional variable. - m = match deadline { - None => self.cvar.wait(m).unwrap(), - Some(deadline) => { - let now = Instant::now(); - if now < deadline { - // We could check for a timeout here, in the return value of wait_timeout, - // but in the case that a timeout and an unpark arrive simultaneously, we - // prefer to report the former. - self.cvar.wait_timeout(m, deadline - now).unwrap().0 - } else { - // We've timed out; swap out the state back to empty on our way out - match self.state.swap(EMPTY, SeqCst) { - NOTIFIED | PARKED => return, - n => panic!("inconsistent park_timeout state: {}", n), - }; - } - } - }; - - if self - .state - .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst) - .is_ok() - { - // got a notification - return; - } - - // Spurious wakeup, go back to sleep. Alternatively, if we timed out, it will be caught - // in the branch above, when we discover the deadline is in the past - } - } - - pub(crate) fn unpark(&self) { - // To ensure the unparked thread will observe any writes we made before this call, we must - // perform a release operation that `park` can synchronize with. To do that we must write - // `NOTIFIED` even if `state` is already `NOTIFIED`. That is why this must be a swap rather - // than a compare-and-swap that returns if it reads `NOTIFIED` on failure. - match self.state.swap(NOTIFIED, SeqCst) { - EMPTY => return, // no one was waiting - NOTIFIED => return, // already unparked - PARKED => {} // gotta go wake someone up - _ => panic!("inconsistent state in unpark"), - } - - // There is a period between when the parked thread sets `state` to `PARKED` (or last - // checked `state` in the case of a spurious wakeup) and when it actually waits on `cvar`. - // If we were to notify during this period it would be ignored and then when the parked - // thread went to sleep it would never wake up. Fortunately, it has `lock` locked at this - // stage so we can acquire `lock` to wait until it is ready to receive the notification. - // - // Releasing `lock` before the call to `notify_one` means that when the parked thread wakes - // it doesn't get woken only to have to wait for us to release `lock`. - drop(self.lock.lock().unwrap()); - self.cvar.notify_one(); - } -} |