src/libstd/sync/condvar.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use prelude::v1::*;
  12
  13 use sync::atomic::{AtomicUsize, Ordering};
  14 use sync::{mutex, MutexGuard, PoisonError};
  15 use sys_common::condvar as sys;
  16 use sys_common::mutex as sys_mutex;
  17 use sys_common::poison::{self, LockResult};
  18 use time::{Instant, Duration};
  19
  20 /// A type indicating whether a timed wait on a condition variable returned
  21 /// due to a time out or not.
  22 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
  23 #[stable(feature = "wait_timeout", since = "1.5.0")]
  24 pub struct WaitTimeoutResult(bool);
  25
  26 impl WaitTimeoutResult {
  27     /// Returns whether the wait was known to have timed out.
  28     #[stable(feature = "wait_timeout", since = "1.5.0")]
  29     pub fn timed_out(&self) -> bool {
  30         self.0
  31     }
  32 }
  33
  34 /// A Condition Variable
  35 ///
  36 /// Condition variables represent the ability to block a thread such that it
  37 /// consumes no CPU time while waiting for an event to occur. Condition
  38 /// variables are typically associated with a boolean predicate (a condition)
  39 /// and a mutex. The predicate is always verified inside of the mutex before
  40 /// determining that thread must block.
  41 ///
  42 /// Functions in this module will block the current **thread** of execution and
  43 /// are bindings to system-provided condition variables where possible. Note
  44 /// that this module places one additional restriction over the system condition
  45 /// variables: each condvar can be used with precisely one mutex at runtime. Any
  46 /// attempt to use multiple mutexes on the same condition variable will result
  47 /// in a runtime panic. If this is not desired, then the unsafe primitives in
  48 /// `sys` do not have this restriction but may result in undefined behavior.
  49 ///
  50 /// # Examples
  51 ///
  52 /// ```
  53 /// use std::sync::{Arc, Mutex, Condvar};
  54 /// use std::thread;
  55 ///
  56 /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
  57 /// let pair2 = pair.clone();
  58 ///
  59 /// // Inside of our lock, spawn a new thread, and then wait for it to start
  60 /// thread::spawn(move|| {
  61 ///     let &(ref lock, ref cvar) = &*pair2;
  62 ///     let mut started = lock.lock().unwrap();
  63 ///     *started = true;
  64 ///     cvar.notify_one();
  65 /// });
  66 ///
  67 /// // wait for the thread to start up
  68 /// let &(ref lock, ref cvar) = &*pair;
  69 /// let mut started = lock.lock().unwrap();
  70 /// while !*started {
  71 ///     started = cvar.wait(started).unwrap();
  72 /// }
  73 /// ```
  74 #[stable(feature = "rust1", since = "1.0.0")]
  75 pub struct Condvar { inner: Box<StaticCondvar> }
  76
  77 /// Statically allocated condition variables.
  78 ///
  79 /// This structure is identical to `Condvar` except that it is suitable for use
  80 /// in static initializers for other structures.
  81 ///
  82 /// # Examples
  83 ///
  84 /// ```
  85 /// #![feature(static_condvar)]
  86 ///
  87 /// use std::sync::{StaticCondvar, CONDVAR_INIT};
  88 ///
  89 /// static CVAR: StaticCondvar = CONDVAR_INIT;
  90 /// ```
  91 #[unstable(feature = "static_condvar",
  92            reason = "may be merged with Condvar in the future",
  93            issue = "27717")]
  94 pub struct StaticCondvar {
  95     inner: sys::Condvar,
  96     mutex: AtomicUsize,
  97 }
  98
  99 /// Constant initializer for a statically allocated condition variable.
 100 #[unstable(feature = "static_condvar",
 101            reason = "may be merged with Condvar in the future",
 102            issue = "27717")]
 103 pub const CONDVAR_INIT: StaticCondvar = StaticCondvar::new();
 104
 105 impl Condvar {
 106     /// Creates a new condition variable which is ready to be waited on and
 107     /// notified.
 108     #[stable(feature = "rust1", since = "1.0.0")]
 109     pub fn new() -> Condvar {
 110         Condvar {
 111             inner: box StaticCondvar {
 112                 inner: sys::Condvar::new(),
 113                 mutex: AtomicUsize::new(0),
 114             }
 115         }
 116     }
 117
 118     /// Blocks the current thread until this condition variable receives a
 119     /// notification.
 120     ///
 121     /// This function will atomically unlock the mutex specified (represented by
 122     /// `mutex_guard`) and block the current thread. This means that any calls
 123     /// to `notify_*()` which happen logically after the mutex is unlocked are
 124     /// candidates to wake this thread up. When this function call returns, the
 125     /// lock specified will have been re-acquired.
 126     ///
 127     /// Note that this function is susceptible to spurious wakeups. Condition
 128     /// variables normally have a boolean predicate associated with them, and
 129     /// the predicate must always be checked each time this function returns to
 130     /// protect against spurious wakeups.
 131     ///
 132     /// # Failure
 133     ///
 134     /// This function will return an error if the mutex being waited on is
 135     /// poisoned when this thread re-acquires the lock. For more information,
 136     /// see information about poisoning on the Mutex type.
 137     ///
 138     /// # Panics
 139     ///
 140     /// This function will `panic!()` if it is used with more than one mutex
 141     /// over time. Each condition variable is dynamically bound to exactly one
 142     /// mutex to ensure defined behavior across platforms. If this functionality
 143     /// is not desired, then unsafe primitives in `sys` are provided.
 144     #[stable(feature = "rust1", since = "1.0.0")]
 145     pub fn wait<'a, T>(&self, guard: MutexGuard<'a, T>)
 146                        -> LockResult<MutexGuard<'a, T>> {
 147         unsafe {
 148             let me: &'static Condvar = &*(self as *const _);
 149             me.inner.wait(guard)
 150         }
 151     }
 152
 153     /// Waits on this condition variable for a notification, timing out after a
 154     /// specified duration.
 155     ///
 156     /// The semantics of this function are equivalent to `wait()`
 157     /// except that the thread will be blocked for roughly no longer
 158     /// than `ms` milliseconds. This method should not be used for
 159     /// precise timing due to anomalies such as preemption or platform
 160     /// differences that may not cause the maximum amount of time
 161     /// waited to be precisely `ms`.
 162     ///
 163     /// The returned boolean is `false` only if the timeout is known
 164     /// to have elapsed.
 165     ///
 166     /// Like `wait`, the lock specified will be re-acquired when this function
 167     /// returns, regardless of whether the timeout elapsed or not.
 168     #[stable(feature = "rust1", since = "1.0.0")]
 169     #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::sync::Condvar::wait_timeout`")]
 170     #[allow(deprecated)]
 171     pub fn wait_timeout_ms<'a, T>(&self, guard: MutexGuard<'a, T>, ms: u32)
 172                                   -> LockResult<(MutexGuard<'a, T>, bool)> {
 173         unsafe {
 174             let me: &'static Condvar = &*(self as *const _);
 175             me.inner.wait_timeout_ms(guard, ms)
 176         }
 177     }
 178
 179     /// Waits on this condition variable for a notification, timing out after a
 180     /// specified duration.
 181     ///
 182     /// The semantics of this function are equivalent to `wait()` except that
 183     /// the thread will be blocked for roughly no longer than `dur`. This
 184     /// method should not be used for precise timing due to anomalies such as
 185     /// preemption or platform differences that may not cause the maximum
 186     /// amount of time waited to be precisely `dur`.
 187     ///
 188     /// The returned `WaitTimeoutResult` value indicates if the timeout is
 189     /// known to have elapsed.
 190     ///
 191     /// Like `wait`, the lock specified will be re-acquired when this function
 192     /// returns, regardless of whether the timeout elapsed or not.
 193     #[stable(feature = "wait_timeout", since = "1.5.0")]
 194     pub fn wait_timeout<'a, T>(&self, guard: MutexGuard<'a, T>,
 195                                dur: Duration)
 196                                -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
 197         unsafe {
 198             let me: &'static Condvar = &*(self as *const _);
 199             me.inner.wait_timeout(guard, dur)
 200         }
 201     }
 202
 203     /// Waits on this condition variable for a notification, timing out after a
 204     /// specified duration.
 205     ///
 206     /// The semantics of this function are equivalent to `wait_timeout` except
 207     /// that the implementation will repeatedly wait while the duration has not
 208     /// passed and the provided function returns `false`.
 209     #[unstable(feature = "wait_timeout_with",
 210                reason = "unsure if this API is broadly needed or what form it should take",
 211                issue = "27748")]
 212     pub fn wait_timeout_with<'a, T, F>(&self,
 213                                        guard: MutexGuard<'a, T>,
 214                                        dur: Duration,
 215                                        f: F)
 216                                        -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
 217             where F: FnMut(LockResult<&mut T>) -> bool {
 218         unsafe {
 219             let me: &'static Condvar = &*(self as *const _);
 220             me.inner.wait_timeout_with(guard, dur, f)
 221         }
 222     }
 223
 224     /// Wakes up one blocked thread on this condvar.
 225     ///
 226     /// If there is a blocked thread on this condition variable, then it will
 227     /// be woken up from its call to `wait` or `wait_timeout`. Calls to
 228     /// `notify_one` are not buffered in any way.
 229     ///
 230     /// To wake up all threads, see `notify_all()`.
 231     #[stable(feature = "rust1", since = "1.0.0")]
 232     pub fn notify_one(&self) { unsafe { self.inner.inner.notify_one() } }
 233
 234     /// Wakes up all blocked threads on this condvar.
 235     ///
 236     /// This method will ensure that any current waiters on the condition
 237     /// variable are awoken. Calls to `notify_all()` are not buffered in any
 238     /// way.
 239     ///
 240     /// To wake up only one thread, see `notify_one()`.
 241     #[stable(feature = "rust1", since = "1.0.0")]
 242     pub fn notify_all(&self) { unsafe { self.inner.inner.notify_all() } }
 243 }
 244
 245 #[stable(feature = "rust1", since = "1.0.0")]
 246 impl Drop for Condvar {
 247     fn drop(&mut self) {
 248         unsafe { self.inner.inner.destroy() }
 249     }
 250 }
 251
 252 impl StaticCondvar {
 253     /// Creates a new condition variable
 254     #[unstable(feature = "static_condvar",
 255                reason = "may be merged with Condvar in the future",
 256                issue = "27717")]
 257     pub const fn new() -> StaticCondvar {
 258         StaticCondvar {
 259             inner: sys::Condvar::new(),
 260             mutex: AtomicUsize::new(0),
 261         }
 262     }
 263
 264     /// Blocks the current thread until this condition variable receives a
 265     /// notification.
 266     ///
 267     /// See `Condvar::wait`.
 268     #[unstable(feature = "static_condvar",
 269                reason = "may be merged with Condvar in the future",
 270                issue = "27717")]
 271     pub fn wait<'a, T>(&'static self, guard: MutexGuard<'a, T>)
 272                        -> LockResult<MutexGuard<'a, T>> {
 273         let poisoned = unsafe {
 274             let lock = mutex::guard_lock(&guard);
 275             self.verify(lock);
 276             self.inner.wait(lock);
 277             mutex::guard_poison(&guard).get()
 278         };
 279         if poisoned {
 280             Err(PoisonError::new(guard))
 281         } else {
 282             Ok(guard)
 283         }
 284     }
 285
 286     /// Waits on this condition variable for a notification, timing out after a
 287     /// specified duration.
 288     ///
 289     /// See `Condvar::wait_timeout`.
 290     #[unstable(feature = "static_condvar",
 291                reason = "may be merged with Condvar in the future",
 292                issue = "27717")]
 293     #[rustc_deprecated(since = "1.6.0",
 294                        reason = "replaced by `std::sync::StaticCondvar::wait_timeout`")]
 295     pub fn wait_timeout_ms<'a, T>(&'static self, guard: MutexGuard<'a, T>, ms: u32)
 296                                   -> LockResult<(MutexGuard<'a, T>, bool)> {
 297         match self.wait_timeout(guard, Duration::from_millis(ms as u64)) {
 298             Ok((guard, timed_out)) => Ok((guard, !timed_out.timed_out())),
 299             Err(poison) => {
 300                 let (guard, timed_out) = poison.into_inner();
 301                 Err(PoisonError::new((guard, !timed_out.timed_out())))
 302             }
 303         }
 304     }
 305
 306     /// Waits on this condition variable for a notification, timing out after a
 307     /// specified duration.
 308     ///
 309     /// See `Condvar::wait_timeout`.
 310     #[unstable(feature = "static_condvar",
 311                reason = "may be merged with Condvar in the future",
 312                issue = "27717")]
 313     pub fn wait_timeout<'a, T>(&'static self,
 314                                guard: MutexGuard<'a, T>,
 315                                timeout: Duration)
 316                                -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
 317         let (poisoned, result) = unsafe {
 318             let lock = mutex::guard_lock(&guard);
 319             self.verify(lock);
 320             let success = self.inner.wait_timeout(lock, timeout);
 321             (mutex::guard_poison(&guard).get(), WaitTimeoutResult(!success))
 322         };
 323         if poisoned {
 324             Err(PoisonError::new((guard, result)))
 325         } else {
 326             Ok((guard, result))
 327         }
 328     }
 329
 330     /// Waits on this condition variable for a notification, timing out after a
 331     /// specified duration.
 332     ///
 333     /// The implementation will repeatedly wait while the duration has not
 334     /// passed and the function returns `false`.
 335     ///
 336     /// See `Condvar::wait_timeout_with`.
 337     #[unstable(feature = "static_condvar",
 338                reason = "may be merged with Condvar in the future",
 339                issue = "27717")]
 340     pub fn wait_timeout_with<'a, T, F>(&'static self,
 341                                        guard: MutexGuard<'a, T>,
 342                                        dur: Duration,
 343                                        mut f: F)
 344                                        -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
 345             where F: FnMut(LockResult<&mut T>) -> bool {
 346         // This could be made more efficient by pushing the implementation into
 347         // sys::condvar
 348         let start = Instant::now();
 349         let mut guard_result: LockResult<MutexGuard<'a, T>> = Ok(guard);
 350         while !f(guard_result
 351                     .as_mut()
 352                     .map(|g| &mut **g)
 353                     .map_err(|e| PoisonError::new(&mut **e.get_mut()))) {
 354             let consumed = start.elapsed();
 355             let guard = guard_result.unwrap_or_else(|e| e.into_inner());
 356             let (new_guard_result, timed_out) = if consumed > dur {
 357                 (Ok(guard), WaitTimeoutResult(true))
 358             } else {
 359                 match self.wait_timeout(guard, dur - consumed) {
 360                     Ok((new_guard, timed_out)) => (Ok(new_guard), timed_out),
 361                     Err(err) => {
 362                         let (new_guard, no_timeout) = err.into_inner();
 363                         (Err(PoisonError::new(new_guard)), no_timeout)
 364                     }
 365                 }
 366             };
 367             guard_result = new_guard_result;
 368             if timed_out.timed_out() {
 369                 let result = f(guard_result
 370                                     .as_mut()
 371                                     .map(|g| &mut **g)
 372                                     .map_err(|e| PoisonError::new(&mut **e.get_mut())));
 373                 let result = WaitTimeoutResult(!result);
 374                 return poison::map_result(guard_result, |g| (g, result));
 375             }
 376         }
 377
 378         poison::map_result(guard_result, |g| (g, WaitTimeoutResult(false)))
 379     }
 380
 381     /// Wakes up one blocked thread on this condvar.
 382     ///
 383     /// See `Condvar::notify_one`.
 384     #[unstable(feature = "static_condvar",
 385                reason = "may be merged with Condvar in the future",
 386                issue = "27717")]
 387     pub fn notify_one(&'static self) { unsafe { self.inner.notify_one() } }
 388
 389     /// Wakes up all blocked threads on this condvar.
 390     ///
 391     /// See `Condvar::notify_all`.
 392     #[unstable(feature = "static_condvar",
 393                reason = "may be merged with Condvar in the future",
 394                issue = "27717")]
 395     pub fn notify_all(&'static self) { unsafe { self.inner.notify_all() } }
 396
 397     /// Deallocates all resources associated with this static condvar.
 398     ///
 399     /// This method is unsafe to call as there is no guarantee that there are no
 400     /// active users of the condvar, and this also doesn't prevent any future
 401     /// users of the condvar. This method is required to be called to not leak
 402     /// memory on all platforms.
 403     #[unstable(feature = "static_condvar",
 404                reason = "may be merged with Condvar in the future",
 405                issue = "27717")]
 406     pub unsafe fn destroy(&'static self) {
 407         self.inner.destroy()
 408     }
 409
 410     fn verify(&self, mutex: &sys_mutex::Mutex) {
 411         let addr = mutex as *const _ as usize;
 412         match self.mutex.compare_and_swap(0, addr, Ordering::SeqCst) {
 413             // If we got out 0, then we have successfully bound the mutex to
 414             // this cvar.
 415             0 => {}
 416
 417             // If we get out a value that's the same as `addr`, then someone
 418             // already beat us to the punch.
 419             n if n == addr => {}
 420
 421             // Anything else and we're using more than one mutex on this cvar,
 422             // which is currently disallowed.
 423             _ => panic!("attempted to use a condition variable with two \
 424                          mutexes"),
 425         }
 426     }
 427 }
 428
 429 #[cfg(test)]
 430 mod tests {
 431     use prelude::v1::*;
 432
 433     use super::StaticCondvar;
 434     use sync::mpsc::channel;
 435     use sync::{StaticMutex, Condvar, Mutex, Arc};
 436     use sync::atomic::{AtomicUsize, Ordering};
 437     use thread;
 438     use time::Duration;
 439     use u32;
 440
 441     #[test]
 442     fn smoke() {
 443         let c = Condvar::new();
 444         c.notify_one();
 445         c.notify_all();
 446     }
 447
 448     #[test]
 449     fn static_smoke() {
 450         static C: StaticCondvar = StaticCondvar::new();
 451         C.notify_one();
 452         C.notify_all();
 453         unsafe { C.destroy(); }
 454     }
 455
 456     #[test]
 457     fn notify_one() {
 458         static C: StaticCondvar = StaticCondvar::new();
 459         static M: StaticMutex = StaticMutex::new();
 460
 461         let g = M.lock().unwrap();
 462         let _t = thread::spawn(move|| {
 463             let _g = M.lock().unwrap();
 464             C.notify_one();
 465         });
 466         let g = C.wait(g).unwrap();
 467         drop(g);
 468         unsafe { C.destroy(); M.destroy(); }
 469     }
 470
 471     #[test]
 472     fn notify_all() {
 473         const N: usize = 10;
 474
 475         let data = Arc::new((Mutex::new(0), Condvar::new()));
 476         let (tx, rx) = channel();
 477         for _ in 0..N {
 478             let data = data.clone();
 479             let tx = tx.clone();
 480             thread::spawn(move|| {
 481                 let &(ref lock, ref cond) = &*data;
 482                 let mut cnt = lock.lock().unwrap();
 483                 *cnt += 1;
 484                 if *cnt == N {
 485                     tx.send(()).unwrap();
 486                 }
 487                 while *cnt != 0 {
 488                     cnt = cond.wait(cnt).unwrap();
 489                 }
 490                 tx.send(()).unwrap();
 491             });
 492         }
 493         drop(tx);
 494
 495         let &(ref lock, ref cond) = &*data;
 496         rx.recv().unwrap();
 497         let mut cnt = lock.lock().unwrap();
 498         *cnt = 0;
 499         cond.notify_all();
 500         drop(cnt);
 501
 502         for _ in 0..N {
 503             rx.recv().unwrap();
 504         }
 505     }
 506
 507     #[test]
 508     fn wait_timeout_ms() {
 509         static C: StaticCondvar = StaticCondvar::new();
 510         static M: StaticMutex = StaticMutex::new();
 511
 512         let g = M.lock().unwrap();
 513         let (g, _no_timeout) = C.wait_timeout_ms(g, 1).unwrap();
 514         // spurious wakeups mean this isn't necessarily true
 515         // assert!(!no_timeout);
 516         let _t = thread::spawn(move || {
 517             let _g = M.lock().unwrap();
 518             C.notify_one();
 519         });
 520         let (g, no_timeout) = C.wait_timeout_ms(g, u32::MAX).unwrap();
 521         assert!(no_timeout);
 522         drop(g);
 523         unsafe { C.destroy(); M.destroy(); }
 524     }
 525
 526     #[test]
 527     fn wait_timeout_with() {
 528         static C: StaticCondvar = StaticCondvar::new();
 529         static M: StaticMutex = StaticMutex::new();
 530         static S: AtomicUsize = AtomicUsize::new(0);
 531
 532         let g = M.lock().unwrap();
 533         let (g, timed_out) = C.wait_timeout_with(g, Duration::new(0, 1000), |_| {
 534             false
 535         }).unwrap();
 536         assert!(timed_out.timed_out());
 537
 538         let (tx, rx) = channel();
 539         let _t = thread::spawn(move || {
 540             rx.recv().unwrap();
 541             let g = M.lock().unwrap();
 542             S.store(1, Ordering::SeqCst);
 543             C.notify_one();
 544             drop(g);
 545
 546             rx.recv().unwrap();
 547             let g = M.lock().unwrap();
 548             S.store(2, Ordering::SeqCst);
 549             C.notify_one();
 550             drop(g);
 551
 552             rx.recv().unwrap();
 553             let _g = M.lock().unwrap();
 554             S.store(3, Ordering::SeqCst);
 555             C.notify_one();
 556         });
 557
 558         let mut state = 0;
 559         let day = 24 * 60 * 60;
 560         let (_g, timed_out) = C.wait_timeout_with(g, Duration::new(day, 0), |_| {
 561             assert_eq!(state, S.load(Ordering::SeqCst));
 562             tx.send(()).unwrap();
 563             state += 1;
 564             match state {
 565                 1|2 => false,
 566                 _ => true,
 567             }
 568         }).unwrap();
 569         assert!(!timed_out.timed_out());
 570     }
 571
 572     #[test]
 573     #[should_panic]
 574     fn two_mutexes() {
 575         static M1: StaticMutex = StaticMutex::new();
 576         static M2: StaticMutex = StaticMutex::new();
 577         static C: StaticCondvar = StaticCondvar::new();
 578
 579         let mut g = M1.lock().unwrap();
 580         let _t = thread::spawn(move|| {
 581             let _g = M1.lock().unwrap();
 582             C.notify_one();
 583         });
 584         g = C.wait(g).unwrap();
 585         drop(g);
 586
 587         let _ = C.wait(M2.lock().unwrap()).unwrap();
 588     }
 589 }