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// 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 prelude::*; use sync::atomic::{mod, AtomicUint}; use sync::poison::{mod, LockResult}; use sys_common::condvar as sys; use sys_common::mutex as sys_mutex; use time::Duration; use sync::{mutex, MutexGuard}; /// 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. /// /// # Example /// /// ``` /// use std::sync::{Arc, Mutex, Condvar}; /// use std::thread::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(); /// }).detach(); /// /// // 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] pub struct Condvar { inner: Box<StaticCondvar> } unsafe impl Send for Condvar {} unsafe impl Sync for Condvar {} /// Statically allocated condition variables. /// /// This structure is identical to `Condvar` except that it is suitable for use /// in static initializers for other structures. /// /// # Example /// /// ``` /// use std::sync::{StaticCondvar, CONDVAR_INIT}; /// /// static CVAR: StaticCondvar = CONDVAR_INIT; /// ``` #[unstable = "may be merged with Condvar in the future"] pub struct StaticCondvar { inner: sys::Condvar, mutex: AtomicUint, } unsafe impl Send for StaticCondvar {} unsafe impl Sync for StaticCondvar {} /// Constant initializer for a statically allocated condition variable. #[unstable = "may be merged with Condvar in the future"] pub const CONDVAR_INIT: StaticCondvar = StaticCondvar { inner: sys::CONDVAR_INIT, mutex: atomic::INIT_ATOMIC_UINT, }; impl Condvar { /// Creates a new condition variable which is ready to be waited on and /// notified. #[stable] pub fn new() -> Condvar { Condvar { inner: box StaticCondvar { inner: unsafe { sys::Condvar::new() }, mutex: AtomicUint::new(0), } } } /// Block 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. /// /// # Failure /// /// 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] pub fn wait<'a, T>(&self, guard: MutexGuard<'a, T>) -> LockResult<MutexGuard<'a, T>> { unsafe { let me: &'static Condvar = &*(self as *const _); me.inner.wait(guard) } } /// Wait 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`. /// /// If the wait timed out, then `false` will be returned. Otherwise if a /// notification was received then `true` will be returned. /// /// Like `wait`, the lock specified will be re-acquired when this function /// returns, regardless of whether the timeout elapsed or not. // Note that this method is *not* public, and this is quite intentional // because we're not quite sure about the semantics of relative vs absolute // durations or how the timing guarantees play into what the system APIs // provide. There are also additional concerns about the unix-specific // implementation which may need to be addressed. #[allow(dead_code)] fn wait_timeout<'a, T>(&self, guard: MutexGuard<'a, T>, dur: Duration) -> LockResult<(MutexGuard<'a, T>, bool)> { unsafe { let me: &'static Condvar = &*(self as *const _); me.inner.wait_timeout(guard, dur) } } /// Wake 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_one()`. #[stable] pub fn notify_one(&self) { unsafe { self.inner.inner.notify_one() } } /// Wake 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] pub fn notify_all(&self) { unsafe { self.inner.inner.notify_all() } } } impl Drop for Condvar { fn drop(&mut self) { unsafe { self.inner.inner.destroy() } } } impl StaticCondvar { /// Block the current thread until this condition variable receives a /// notification. /// /// See `Condvar::wait`. #[unstable = "may be merged with Condvar in the future"] pub fn wait<'a, T>(&'static 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(poison::new_poison_error(guard)) } else { Ok(guard) } } /// Wait on this condition variable for a notification, timing out after a /// specified duration. /// /// See `Condvar::wait_timeout`. #[allow(dead_code)] // may want to stabilize this later, see wait_timeout above fn wait_timeout<'a, T>(&'static self, guard: MutexGuard<'a, T>, dur: Duration) -> LockResult<(MutexGuard<'a, T>, bool)> { let (poisoned, success) = unsafe { let lock = mutex::guard_lock(&guard); self.verify(lock); let success = self.inner.wait_timeout(lock, dur); (mutex::guard_poison(&guard).get(), success) }; if poisoned { Err(poison::new_poison_error((guard, success))) } else { Ok((guard, success)) } } /// Wake up one blocked thread on this condvar. /// /// See `Condvar::notify_one`. #[unstable = "may be merged with Condvar in the future"] pub fn notify_one(&'static self) { unsafe { self.inner.notify_one() } } /// Wake up all blocked threads on this condvar. /// /// See `Condvar::notify_all`. #[unstable = "may be merged with Condvar in the future"] pub fn notify_all(&'static self) { unsafe { self.inner.notify_all() } } /// Deallocate all resources associated with this static condvar. /// /// This method is unsafe to call as there is no guarantee that there are no /// active users of the condvar, and this also doesn't prevent any future /// users of the condvar. This method is required to be called to not leak /// memory on all platforms. #[unstable = "may be merged with Condvar in the future"] pub unsafe fn destroy(&'static self) { self.inner.destroy() } fn verify(&self, mutex: &sys_mutex::Mutex) { let addr = mutex as *const _ as uint; match self.mutex.compare_and_swap(0, addr, atomic::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"), } } } #[cfg(test)] mod tests { use prelude::*; use time::Duration; use super::{StaticCondvar, CONDVAR_INIT}; use sync::{StaticMutex, MUTEX_INIT, Condvar, Mutex, Arc}; #[test] fn smoke() { let c = Condvar::new(); c.notify_one(); c.notify_all(); } #[test] fn static_smoke() { static C: StaticCondvar = CONDVAR_INIT; C.notify_one(); C.notify_all(); unsafe { C.destroy(); } } #[test] fn notify_one() { static C: StaticCondvar = CONDVAR_INIT; static M: StaticMutex = MUTEX_INIT; let g = M.lock().unwrap(); spawn(move|| { let _g = M.lock().unwrap(); C.notify_one(); }); let g = C.wait(g).unwrap(); drop(g); unsafe { C.destroy(); M.destroy(); } } #[test] fn notify_all() { const N: uint = 10; let data = Arc::new((Mutex::new(0), Condvar::new())); let (tx, rx) = channel(); for _ in range(0, N) { let data = data.clone(); let tx = tx.clone(); spawn(move|| { let &(ref lock, ref cond) = &*data; let mut cnt = lock.lock().unwrap(); *cnt += 1; if *cnt == N { tx.send(()); } while *cnt != 0 { cnt = cond.wait(cnt).unwrap(); } tx.send(()); }); } drop(tx); let &(ref lock, ref cond) = &*data; rx.recv(); let mut cnt = lock.lock().unwrap(); *cnt = 0; cond.notify_all(); drop(cnt); for _ in range(0, N) { rx.recv(); } } #[test] fn wait_timeout() { static C: StaticCondvar = CONDVAR_INIT; static M: StaticMutex = MUTEX_INIT; let g = M.lock().unwrap(); let (g, success) = C.wait_timeout(g, Duration::nanoseconds(1000)).unwrap(); assert!(!success); spawn(move|| { let _g = M.lock().unwrap(); C.notify_one(); }); let (g, success) = C.wait_timeout(g, Duration::days(1)).unwrap(); assert!(success); drop(g); unsafe { C.destroy(); M.destroy(); } } #[test] #[should_fail] fn two_mutexes() { static M1: StaticMutex = MUTEX_INIT; static M2: StaticMutex = MUTEX_INIT; static C: StaticCondvar = CONDVAR_INIT; let mut g = M1.lock().unwrap(); spawn(move|| { let _g = M1.lock().unwrap(); C.notify_one(); }); g = C.wait(g).unwrap(); drop(g); C.wait(M2.lock().unwrap()).unwrap(); } }