src/libstd/sync/condvar.rs - rust - Git at Google

 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.

 use sync::atomic::{AtomicUsize, Ordering};
 use sync::{mutex, MutexGuard, PoisonError};
 use sys_common::condvar as sys;
 use sys_common::mutex as sys_mutex;
 use sys_common::poison::{self, LockResult};
 use time::Duration;

 /// A type indicating whether a timed wait on a condition variable returned
 /// due to a time out or not.
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
 #[stable(feature = "wait_timeout", since = "1.5.0")]
 pub struct WaitTimeoutResult(bool);

 impl WaitTimeoutResult {
     /// Returns whether the wait was known to have timed out.
     #[stable(feature = "wait_timeout", since = "1.5.0")]
     pub fn timed_out(&self) -> bool {
         self.0
     }
 }

 /// A Condition Variable
 ///
 /// Condition variables represent the ability to block a thread such that it
 /// consumes no CPU time while waiting for an event to occur. Condition
 /// variables are typically associated with a boolean predicate (a condition)
 /// and a mutex. The predicate is always verified inside of the mutex before
 /// determining that thread must block.
 ///
 /// Functions in this module will block the current **thread** of execution and
 /// are bindings to system-provided condition variables where possible. Note
 /// that this module places one additional restriction over the system condition
 /// variables: each condvar can be used with precisely one mutex at runtime. Any
 /// attempt to use multiple mutexes on the same condition variable will result
 /// in a runtime panic. If this is not desired, then the unsafe primitives in
 /// `sys` do not have this restriction but may result in undefined behavior.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::sync::{Arc, Mutex, Condvar};
 /// use std::thread;
 ///
 /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
 /// let pair2 = pair.clone();
 ///
 /// // Inside of our lock, spawn a new thread, and then wait for it to start
 /// thread::spawn(move|| {
 ///     let &(ref lock, ref cvar) = &*pair2;
 ///     let mut started = lock.lock().unwrap();
 ///     *started = true;
 ///     cvar.notify_one();
 /// });
 ///
 /// // wait for the thread to start up
 /// let &(ref lock, ref cvar) = &*pair;
 /// let mut started = lock.lock().unwrap();
 /// while !*started {
 ///     started = cvar.wait(started).unwrap();
 /// }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Condvar {
     inner: Box<sys::Condvar>,
     mutex: AtomicUsize,
 }

 impl Condvar {
     /// Creates a new condition variable which is ready to be waited on and
     /// notified.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new() -> Condvar {
         let mut c = Condvar {
             inner: box sys::Condvar::new(),
             mutex: AtomicUsize::new(0),
         };
         unsafe {
             c.inner.init();
         }
         c
     }

     /// Blocks the current thread until this condition variable receives a
     /// notification.
     ///
     /// This function will atomically unlock the mutex specified (represented by
     /// `mutex_guard`) and block the current thread. This means that any calls
     /// to `notify_*()` which happen logically after the mutex is unlocked are
     /// candidates to wake this thread up. When this function call returns, the
     /// lock specified will have been re-acquired.
     ///
     /// Note that this function is susceptible to spurious wakeups. Condition
     /// variables normally have a boolean predicate associated with them, and
     /// the predicate must always be checked each time this function returns to
     /// protect against spurious wakeups.
     ///
     /// # Errors
     ///
     /// This function will return an error if the mutex being waited on is
     /// poisoned when this thread re-acquires the lock. For more information,
     /// see information about poisoning on the Mutex type.
     ///
     /// # Panics
     ///
     /// This function will `panic!()` if it is used with more than one mutex
     /// over time. Each condition variable is dynamically bound to exactly one
     /// mutex to ensure defined behavior across platforms. If this functionality
     /// is not desired, then unsafe primitives in `sys` are provided.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn wait<'a, T>(&self, guard: MutexGuard<'a, T>)
                        -> LockResult<MutexGuard<'a, T>> {
         let poisoned = unsafe {
             let lock = mutex::guard_lock(&guard);
             self.verify(lock);
             self.inner.wait(lock);
             mutex::guard_poison(&guard).get()
         };
         if poisoned {
             Err(PoisonError::new(guard))
         } else {
             Ok(guard)
         }
     }

     /// Waits on this condition variable for a notification, timing out after a
     /// specified duration.
     ///
     /// The semantics of this function are equivalent to `wait()`
     /// except that the thread will be blocked for roughly no longer
     /// than `ms` milliseconds. This method should not be used for
     /// precise timing due to anomalies such as preemption or platform
     /// differences that may not cause the maximum amount of time
     /// waited to be precisely `ms`.
     ///
     /// Note that the best effort is made to ensure that the time waited is
     /// measured with a monotonic clock, and not affected by the changes made to
     /// the system time.
     ///
     /// The returned boolean is `false` only if the timeout is known
     /// to have elapsed.
     ///
     /// Like `wait`, the lock specified will be re-acquired when this function
     /// returns, regardless of whether the timeout elapsed or not.
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::sync::Condvar::wait_timeout`")]
     pub fn wait_timeout_ms<'a, T>(&self, guard: MutexGuard<'a, T>, ms: u32)
                                   -> LockResult<(MutexGuard<'a, T>, bool)> {
         let res = self.wait_timeout(guard, Duration::from_millis(ms as u64));
         poison::map_result(res, |(a, b)| {
             (a, !b.timed_out())
         })
     }

     /// Waits on this condition variable for a notification, timing out after a
     /// specified duration.
     ///
     /// The semantics of this function are equivalent to `wait()` except that
     /// the thread will be blocked for roughly no longer than `dur`. This
     /// method should not be used for precise timing due to anomalies such as
     /// preemption or platform differences that may not cause the maximum
     /// amount of time waited to be precisely `dur`.
     ///
     /// Note that the best effort is made to ensure that the time waited is
     /// measured with a monotonic clock, and not affected by the changes made to
     /// the system time.
     ///
     /// The returned `WaitTimeoutResult` value indicates if the timeout is
     /// known to have elapsed.
     ///
     /// Like `wait`, the lock specified will be re-acquired when this function
     /// returns, regardless of whether the timeout elapsed or not.
     #[stable(feature = "wait_timeout", since = "1.5.0")]
     pub fn wait_timeout<'a, T>(&self, guard: MutexGuard<'a, T>,
                                dur: Duration)
                                -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
         let (poisoned, result) = unsafe {
             let lock = mutex::guard_lock(&guard);
             self.verify(lock);
             let success = self.inner.wait_timeout(lock, dur);
             (mutex::guard_poison(&guard).get(), WaitTimeoutResult(!success))
         };
         if poisoned {
             Err(PoisonError::new((guard, result)))
         } else {
             Ok((guard, result))
         }
     }

     /// Wakes up one blocked thread on this condvar.
     ///
     /// If there is a blocked thread on this condition variable, then it will
     /// be woken up from its call to `wait` or `wait_timeout`. Calls to
     /// `notify_one` are not buffered in any way.
     ///
     /// To wake up all threads, see `notify_all()`.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn notify_one(&self) {
         unsafe { self.inner.notify_one() }
     }

     /// Wakes up all blocked threads on this condvar.
     ///
     /// This method will ensure that any current waiters on the condition
     /// variable are awoken. Calls to `notify_all()` are not buffered in any
     /// way.
     ///
     /// To wake up only one thread, see `notify_one()`.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn notify_all(&self) {
         unsafe { self.inner.notify_all() }
     }

     fn verify(&self, mutex: &sys_mutex::Mutex) {
         let addr = mutex as *const _ as usize;
         match self.mutex.compare_and_swap(0, addr, Ordering::SeqCst) {
             // If we got out 0, then we have successfully bound the mutex to
             // this cvar.
             0 => {}

             // If we get out a value that's the same as `addr`, then someone
             // already beat us to the punch.
             n if n == addr => {}

             // Anything else and we're using more than one mutex on this cvar,
             // which is currently disallowed.
             _ => panic!("attempted to use a condition variable with two \
                          mutexes"),
         }
     }
 }

 #[stable(feature = "condvar_default", since = "1.9.0")]
 impl Default for Condvar {
     /// Creates a `Condvar` which is ready to be waited on and notified.
     fn default() -> Condvar {
         Condvar::new()
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl Drop for Condvar {
     fn drop(&mut self) {
         unsafe { self.inner.destroy() }
     }
 }

 #[cfg(test)]
 mod tests {
     use sync::mpsc::channel;
     use sync::{Condvar, Mutex, Arc};
     use thread;
     use time::Duration;
     use u32;

     #[test]
     fn smoke() {
         let c = Condvar::new();
         c.notify_one();
         c.notify_all();
     }

     #[test]
     fn notify_one() {
         let m = Arc::new(Mutex::new(()));
         let m2 = m.clone();
         let c = Arc::new(Condvar::new());
         let c2 = c.clone();

         let g = m.lock().unwrap();
         let _t = thread::spawn(move|| {
             let _g = m2.lock().unwrap();
             c2.notify_one();
         });
         let g = c.wait(g).unwrap();
         drop(g);
     }

     #[test]
     fn notify_all() {
         const N: usize = 10;

         let data = Arc::new((Mutex::new(0), Condvar::new()));
         let (tx, rx) = channel();
         for _ in 0..N {
             let data = data.clone();
             let tx = tx.clone();
             thread::spawn(move|| {
                 let &(ref lock, ref cond) = &*data;
                 let mut cnt = lock.lock().unwrap();
                 *cnt += 1;
                 if *cnt == N {
                     tx.send(()).unwrap();
                 }
                 while *cnt != 0 {
                     cnt = cond.wait(cnt).unwrap();
                 }
                 tx.send(()).unwrap();
             });
         }
         drop(tx);

         let &(ref lock, ref cond) = &*data;
         rx.recv().unwrap();
         let mut cnt = lock.lock().unwrap();
         *cnt = 0;
         cond.notify_all();
         drop(cnt);

         for _ in 0..N {
             rx.recv().unwrap();
         }
     }

     #[test]
     fn wait_timeout_ms() {
         let m = Arc::new(Mutex::new(()));
         let m2 = m.clone();
         let c = Arc::new(Condvar::new());
         let c2 = c.clone();

         let g = m.lock().unwrap();
         let (g, _no_timeout) = c.wait_timeout(g, Duration::from_millis(1)).unwrap();
         // spurious wakeups mean this isn't necessarily true
         // assert!(!no_timeout);
         let _t = thread::spawn(move || {
             let _g = m2.lock().unwrap();
             c2.notify_one();
         });
         let (g, timeout_res) = c.wait_timeout(g, Duration::from_millis(u32::MAX as u64)).unwrap();
         assert!(!timeout_res.timed_out());
         drop(g);
     }

     #[test]
     #[should_panic]
     fn two_mutexes() {
         let m = Arc::new(Mutex::new(()));
         let m2 = m.clone();
         let c = Arc::new(Condvar::new());
         let c2 = c.clone();

         let mut g = m.lock().unwrap();
         let _t = thread::spawn(move|| {
             let _g = m2.lock().unwrap();
             c2.notify_one();
         });
         g = c.wait(g).unwrap();
         drop(g);

         let m = Mutex::new(());
         let _ = c.wait(m.lock().unwrap()).unwrap();
     }
 }
	// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
	// file at the top-level directory of this distribution and at
	// http://rust-lang.org/COPYRIGHT.
	//
	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
	// option. This file may not be copied, modified, or distributed
	// except according to those terms.

	use sync::atomic::{AtomicUsize, Ordering};
	use sync::{mutex, MutexGuard, PoisonError};
	use sys_common::condvar as sys;
	use sys_common::mutex as sys_mutex;
	use sys_common::poison::{self, LockResult};
	use time::Duration;

	/// A type indicating whether a timed wait on a condition variable returned
	/// due to a time out or not.
	#[derive(Debug, PartialEq, Eq, Copy, Clone)]
	#[stable(feature = "wait_timeout", since = "1.5.0")]
	pub struct WaitTimeoutResult(bool);

	impl WaitTimeoutResult {
	/// Returns whether the wait was known to have timed out.
	#[stable(feature = "wait_timeout", since = "1.5.0")]
	pub fn timed_out(&self) -> bool {
	self.0
	}
	}

	/// A Condition Variable
	///
	/// Condition variables represent the ability to block a thread such that it
	/// consumes no CPU time while waiting for an event to occur. Condition
	/// variables are typically associated with a boolean predicate (a condition)
	/// and a mutex. The predicate is always verified inside of the mutex before
	/// determining that thread must block.
	///
	/// Functions in this module will block the current thread of execution and
	/// are bindings to system-provided condition variables where possible. Note
	/// that this module places one additional restriction over the system condition
	/// variables: each condvar can be used with precisely one mutex at runtime. Any
	/// attempt to use multiple mutexes on the same condition variable will result
	/// in a runtime panic. If this is not desired, then the unsafe primitives in
	/// `sys` do not have this restriction but may result in undefined behavior.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::{Arc, Mutex, Condvar};
	/// use std::thread;
	///
	/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
	/// let pair2 = pair.clone();
	///
	/// // Inside of our lock, spawn a new thread, and then wait for it to start
	/// thread::spawn(move\|\| {
	/// let &(ref lock, ref cvar) = &*pair2;
	/// let mut started = lock.lock().unwrap();
	/// *started = true;
	/// cvar.notify_one();
	/// });
	///
	/// // wait for the thread to start up
	/// let &(ref lock, ref cvar) = &*pair;
	/// let mut started = lock.lock().unwrap();
	/// while !*started {
	/// started = cvar.wait(started).unwrap();
	/// }
	/// ```
	#[stable(feature = "rust1", since = "1.0.0")]
	pub struct Condvar {
	inner: Box<sys::Condvar>,
	mutex: AtomicUsize,
	}

	impl Condvar {
	/// Creates a new condition variable which is ready to be waited on and
	/// notified.
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn new() -> Condvar {
	let mut c = Condvar {
	inner: box sys::Condvar::new(),
	mutex: AtomicUsize::new(0),
	};
	unsafe {
	c.inner.init();
	}
	c
	}

	/// Blocks the current thread until this condition variable receives a
	/// notification.
	///
	/// This function will atomically unlock the mutex specified (represented by
	/// `mutex_guard`) and block the current thread. This means that any calls
	/// to `notify_*()` which happen logically after the mutex is unlocked are
	/// candidates to wake this thread up. When this function call returns, the
	/// lock specified will have been re-acquired.
	///
	/// Note that this function is susceptible to spurious wakeups. Condition
	/// variables normally have a boolean predicate associated with them, and
	/// the predicate must always be checked each time this function returns to
	/// protect against spurious wakeups.
	///
	/// # Errors
	///
	/// This function will return an error if the mutex being waited on is
	/// poisoned when this thread re-acquires the lock. For more information,
	/// see information about poisoning on the Mutex type.
	///
	/// # Panics
	///
	/// This function will `panic!()` if it is used with more than one mutex
	/// over time. Each condition variable is dynamically bound to exactly one
	/// mutex to ensure defined behavior across platforms. If this functionality
	/// is not desired, then unsafe primitives in `sys` are provided.
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn wait<'a, T>(&self, guard: MutexGuard<'a, T>)
	-> LockResult<MutexGuard<'a, T>> {
	let poisoned = unsafe {
	let lock = mutex::guard_lock(&guard);
	self.verify(lock);
	self.inner.wait(lock);
	mutex::guard_poison(&guard).get()
	};
	if poisoned {
	Err(PoisonError::new(guard))
	} else {
	Ok(guard)
	}
	}

	/// Waits on this condition variable for a notification, timing out after a
	/// specified duration.
	///
	/// The semantics of this function are equivalent to `wait()`
	/// except that the thread will be blocked for roughly no longer
	/// than `ms` milliseconds. This method should not be used for
	/// precise timing due to anomalies such as preemption or platform
	/// differences that may not cause the maximum amount of time
	/// waited to be precisely `ms`.
	///
	/// Note that the best effort is made to ensure that the time waited is
	/// measured with a monotonic clock, and not affected by the changes made to
	/// the system time.
	///
	/// The returned boolean is `false` only if the timeout is known
	/// to have elapsed.
	///
	/// Like `wait`, the lock specified will be re-acquired when this function
	/// returns, regardless of whether the timeout elapsed or not.
	#[stable(feature = "rust1", since = "1.0.0")]
	#[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::sync::Condvar::wait_timeout`")]
	pub fn wait_timeout_ms<'a, T>(&self, guard: MutexGuard<'a, T>, ms: u32)
	-> LockResult<(MutexGuard<'a, T>, bool)> {
	let res = self.wait_timeout(guard, Duration::from_millis(ms as u64));
	poison::map_result(res, \|(a, b)\| {
	(a, !b.timed_out())
	})
	}

	/// Waits on this condition variable for a notification, timing out after a
	/// specified duration.
	///
	/// The semantics of this function are equivalent to `wait()` except that
	/// the thread will be blocked for roughly no longer than `dur`. This
	/// method should not be used for precise timing due to anomalies such as
	/// preemption or platform differences that may not cause the maximum
	/// amount of time waited to be precisely `dur`.
	///
	/// Note that the best effort is made to ensure that the time waited is
	/// measured with a monotonic clock, and not affected by the changes made to
	/// the system time.
	///
	/// The returned `WaitTimeoutResult` value indicates if the timeout is
	/// known to have elapsed.
	///
	/// Like `wait`, the lock specified will be re-acquired when this function
	/// returns, regardless of whether the timeout elapsed or not.
	#[stable(feature = "wait_timeout", since = "1.5.0")]
	pub fn wait_timeout<'a, T>(&self, guard: MutexGuard<'a, T>,
	dur: Duration)
	-> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
	let (poisoned, result) = unsafe {
	let lock = mutex::guard_lock(&guard);
	self.verify(lock);
	let success = self.inner.wait_timeout(lock, dur);
	(mutex::guard_poison(&guard).get(), WaitTimeoutResult(!success))
	};
	if poisoned {
	Err(PoisonError::new((guard, result)))
	} else {
	Ok((guard, result))
	}
	}

	/// Wakes up one blocked thread on this condvar.
	///
	/// If there is a blocked thread on this condition variable, then it will
	/// be woken up from its call to `wait` or `wait_timeout`. Calls to
	/// `notify_one` are not buffered in any way.
	///
	/// To wake up all threads, see `notify_all()`.
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn notify_one(&self) {
	unsafe { self.inner.notify_one() }
	}

	/// Wakes up all blocked threads on this condvar.
	///
	/// This method will ensure that any current waiters on the condition
	/// variable are awoken. Calls to `notify_all()` are not buffered in any
	/// way.
	///
	/// To wake up only one thread, see `notify_one()`.
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn notify_all(&self) {
	unsafe { self.inner.notify_all() }
	}

	fn verify(&self, mutex: &sys_mutex::Mutex) {
	let addr = mutex as *const _ as usize;
	match self.mutex.compare_and_swap(0, addr, Ordering::SeqCst) {
	// If we got out 0, then we have successfully bound the mutex to
	// this cvar.
	0 => {}

	// If we get out a value that's the same as `addr`, then someone
	// already beat us to the punch.
	n if n == addr => {}

	// Anything else and we're using more than one mutex on this cvar,
	// which is currently disallowed.
	_ => panic!("attempted to use a condition variable with two \
	mutexes"),
	}
	}
	}

	#[stable(feature = "condvar_default", since = "1.9.0")]
	impl Default for Condvar {
	/// Creates a `Condvar` which is ready to be waited on and notified.
	fn default() -> Condvar {
	Condvar::new()
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl Drop for Condvar {
	fn drop(&mut self) {
	unsafe { self.inner.destroy() }
	}
	}

	#[cfg(test)]
	mod tests {
	use sync::mpsc::channel;
	use sync::{Condvar, Mutex, Arc};
	use thread;
	use time::Duration;
	use u32;

	#[test]
	fn smoke() {
	let c = Condvar::new();
	c.notify_one();
	c.notify_all();
	}

	#[test]
	fn notify_one() {
	let m = Arc::new(Mutex::new(()));
	let m2 = m.clone();
	let c = Arc::new(Condvar::new());
	let c2 = c.clone();

	let g = m.lock().unwrap();
	let _t = thread::spawn(move\|\| {
	let _g = m2.lock().unwrap();
	c2.notify_one();
	});
	let g = c.wait(g).unwrap();
	drop(g);
	}

	#[test]
	fn notify_all() {
	const N: usize = 10;

	let data = Arc::new((Mutex::new(0), Condvar::new()));
	let (tx, rx) = channel();
	for _ in 0..N {
	let data = data.clone();
	let tx = tx.clone();
	thread::spawn(move\|\| {
	let &(ref lock, ref cond) = &*data;
	let mut cnt = lock.lock().unwrap();
	*cnt += 1;
	if *cnt == N {
	tx.send(()).unwrap();
	}
	while *cnt != 0 {
	cnt = cond.wait(cnt).unwrap();
	}
	tx.send(()).unwrap();
	});
	}
	drop(tx);

	let &(ref lock, ref cond) = &*data;
	rx.recv().unwrap();
	let mut cnt = lock.lock().unwrap();
	*cnt = 0;
	cond.notify_all();
	drop(cnt);

	for _ in 0..N {
	rx.recv().unwrap();
	}
	}

	#[test]
	fn wait_timeout_ms() {
	let m = Arc::new(Mutex::new(()));
	let m2 = m.clone();
	let c = Arc::new(Condvar::new());
	let c2 = c.clone();

	let g = m.lock().unwrap();
	let (g, _no_timeout) = c.wait_timeout(g, Duration::from_millis(1)).unwrap();
	// spurious wakeups mean this isn't necessarily true
	// assert!(!no_timeout);
	let _t = thread::spawn(move \|\| {
	let _g = m2.lock().unwrap();
	c2.notify_one();
	});
	let (g, timeout_res) = c.wait_timeout(g, Duration::from_millis(u32::MAX as u64)).unwrap();
	assert!(!timeout_res.timed_out());
	drop(g);
	}

	#[test]
	#[should_panic]
	fn two_mutexes() {
	let m = Arc::new(Mutex::new(()));
	let m2 = m.clone();
	let c = Arc::new(Condvar::new());
	let c2 = c.clone();

	let mut g = m.lock().unwrap();
	let _t = thread::spawn(move\|\| {
	let _g = m2.lock().unwrap();
	c2.notify_one();
	});
	g = c.wait(g).unwrap();
	drop(g);

	let m = Mutex::new(());
	let _ = c.wait(m.lock().unwrap()).unwrap();
	}
	}