1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562
#[cfg(test)]
mod tests;
use crate::fmt;
use crate::sync::{mutex, poison, LockResult, MutexGuard, PoisonError};
use crate::sys::locks as sys;
use crate::time::{Duration, Instant};
/// A type indicating whether a timed wait on a condition variable returned
/// due to a time out or not.
///
/// It is returned by the [`wait_timeout`] method.
///
/// [`wait_timeout`]: Condvar::wait_timeout
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
#[stable(feature = "wait_timeout", since = "1.5.0")]
pub struct WaitTimeoutResult(bool);
impl WaitTimeoutResult {
/// Returns `true` if the wait was known to have timed out.
///
/// # Examples
///
/// This example spawns a thread which will sleep 20 milliseconds before
/// updating a boolean value and then notifying the condvar.
///
/// The main thread will wait with a 10 millisecond timeout on the condvar
/// and will leave the loop upon timeout.
///
/// ```
/// use std::sync::{Arc, Condvar, Mutex};
/// use std::thread;
/// use std::time::Duration;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move || {
/// let (lock, cvar) = &*pair2;
///
/// // Let's wait 20 milliseconds before notifying the condvar.
/// thread::sleep(Duration::from_millis(20));
///
/// let mut started = lock.lock().unwrap();
/// // We update the boolean value.
/// *started = true;
/// cvar.notify_one();
/// });
///
/// // Wait for the thread to start up.
/// let (lock, cvar) = &*pair;
/// loop {
/// // Let's put a timeout on the condvar's wait.
/// let result = cvar.wait_timeout(lock.lock().unwrap(), Duration::from_millis(10)).unwrap();
/// // 10 milliseconds have passed.
/// if result.1.timed_out() {
/// // timed out now and we can leave.
/// break
/// }
/// }
/// ```
#[must_use]
#[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 a thread must block.
///
/// Functions in this module will block the current **thread** of execution.
/// Note that any attempt to use multiple mutexes on the same condition
/// variable may result in a runtime panic.
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// // Inside of our lock, spawn a new thread, and then wait for it to start.
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// // We notify the condvar that the value has changed.
/// cvar.notify_one();
/// });
///
/// // Wait for the thread to start up.
/// let (lock, 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: sys::Condvar,
}
impl Condvar {
/// Creates a new condition variable which is ready to be waited on and
/// notified.
///
/// # Examples
///
/// ```
/// use std::sync::Condvar;
///
/// let condvar = Condvar::new();
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
#[must_use]
#[inline]
pub const fn new() -> Condvar {
Condvar { inner: sys::Condvar::new() }
}
/// Blocks the current thread until this condition variable receives a
/// notification.
///
/// This function will atomically unlock the mutex specified (represented by
/// `guard`) and block the current thread. This means that any calls
/// to [`notify_one`] or [`notify_all`] 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 may [`panic!`] if it is used with more than one mutex
/// over time.
///
/// [`notify_one`]: Self::notify_one
/// [`notify_all`]: Self::notify_all
/// [poisoning]: super::Mutex#poisoning
/// [`Mutex`]: super::Mutex
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// // We notify the condvar that the value has changed.
/// cvar.notify_one();
/// });
///
/// // Wait for the thread to start up.
/// let (lock, cvar) = &*pair;
/// let mut started = lock.lock().unwrap();
/// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
/// while !*started {
/// started = cvar.wait(started).unwrap();
/// }
/// ```
#[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.inner.wait(lock);
mutex::guard_poison(&guard).get()
};
if poisoned { Err(PoisonError::new(guard)) } else { Ok(guard) }
}
/// Blocks the current thread until this condition variable receives a
/// notification and the provided condition is false.
///
/// This function will atomically unlock the mutex specified (represented by
/// `guard`) and block the current thread. This means that any calls
/// to [`notify_one`] or [`notify_all`] 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.
///
/// # 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.
///
/// [`notify_one`]: Self::notify_one
/// [`notify_all`]: Self::notify_all
/// [poisoning]: super::Mutex#poisoning
/// [`Mutex`]: super::Mutex
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
///
/// let pair = Arc::new((Mutex::new(true), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut pending = lock.lock().unwrap();
/// *pending = false;
/// // We notify the condvar that the value has changed.
/// cvar.notify_one();
/// });
///
/// // Wait for the thread to start up.
/// let (lock, cvar) = &*pair;
/// // As long as the value inside the `Mutex<bool>` is `true`, we wait.
/// let _guard = cvar.wait_while(lock.lock().unwrap(), |pending| { *pending }).unwrap();
/// ```
#[stable(feature = "wait_until", since = "1.42.0")]
pub fn wait_while<'a, T, F>(
&self,
mut guard: MutexGuard<'a, T>,
mut condition: F,
) -> LockResult<MutexGuard<'a, T>>
where
F: FnMut(&mut T) -> bool,
{
while condition(&mut *guard) {
guard = self.wait(guard)?;
}
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 might 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.
///
/// [`wait`]: Self::wait
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// // We notify the condvar that the value has changed.
/// cvar.notify_one();
/// });
///
/// // Wait for the thread to start up.
/// let (lock, cvar) = &*pair;
/// let mut started = lock.lock().unwrap();
/// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
/// loop {
/// let result = cvar.wait_timeout_ms(started, 10).unwrap();
/// // 10 milliseconds have passed, or maybe the value changed!
/// started = result.0;
/// if *started == true {
/// // We received the notification and the value has been updated, we can leave.
/// break
/// }
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[deprecated(since = "1.6.0", note = "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 might 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. 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. Additionally, it is
/// typically desirable for the timeout to not exceed some duration in
/// spite of spurious wakes, thus the sleep-duration is decremented by the
/// amount slept. Alternatively, use the `wait_timeout_while` method
/// to wait with a timeout while a predicate is true.
///
/// 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.
///
/// [`wait`]: Self::wait
/// [`wait_timeout_while`]: Self::wait_timeout_while
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
/// use std::time::Duration;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// // We notify the condvar that the value has changed.
/// cvar.notify_one();
/// });
///
/// // wait for the thread to start up
/// let (lock, cvar) = &*pair;
/// let mut started = lock.lock().unwrap();
/// // as long as the value inside the `Mutex<bool>` is `false`, we wait
/// loop {
/// let result = cvar.wait_timeout(started, Duration::from_millis(10)).unwrap();
/// // 10 milliseconds have passed, or maybe the value changed!
/// started = result.0;
/// if *started == true {
/// // We received the notification and the value has been updated, we can leave.
/// break
/// }
/// }
/// ```
#[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);
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)) }
}
/// Waits on this condition variable for a notification, timing out after a
/// specified duration.
///
/// The semantics of this function are equivalent to [`wait_while`] 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 might 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 without the condition being met.
///
/// Like [`wait_while`], the lock specified will be re-acquired when this
/// function returns, regardless of whether the timeout elapsed or not.
///
/// [`wait_while`]: Self::wait_while
/// [`wait_timeout`]: Self::wait_timeout
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
/// use std::time::Duration;
///
/// let pair = Arc::new((Mutex::new(true), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut pending = lock.lock().unwrap();
/// *pending = false;
/// // We notify the condvar that the value has changed.
/// cvar.notify_one();
/// });
///
/// // wait for the thread to start up
/// let (lock, cvar) = &*pair;
/// let result = cvar.wait_timeout_while(
/// lock.lock().unwrap(),
/// Duration::from_millis(100),
/// |&mut pending| pending,
/// ).unwrap();
/// if result.1.timed_out() {
/// // timed-out without the condition ever evaluating to false.
/// }
/// // access the locked mutex via result.0
/// ```
#[stable(feature = "wait_timeout_until", since = "1.42.0")]
pub fn wait_timeout_while<'a, T, F>(
&self,
mut guard: MutexGuard<'a, T>,
dur: Duration,
mut condition: F,
) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
where
F: FnMut(&mut T) -> bool,
{
let start = Instant::now();
loop {
if !condition(&mut *guard) {
return Ok((guard, WaitTimeoutResult(false)));
}
let timeout = match dur.checked_sub(start.elapsed()) {
Some(timeout) => timeout,
None => return Ok((guard, WaitTimeoutResult(true))),
};
guard = self.wait_timeout(guard, timeout)?.0;
}
}
/// 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`].
///
/// [`wait`]: Self::wait
/// [`wait_timeout`]: Self::wait_timeout
/// [`notify_all`]: Self::notify_all
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// // We notify the condvar that the value has changed.
/// cvar.notify_one();
/// });
///
/// // Wait for the thread to start up.
/// let (lock, cvar) = &*pair;
/// let mut started = lock.lock().unwrap();
/// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
/// while !*started {
/// started = cvar.wait(started).unwrap();
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn notify_one(&self) {
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`].
///
/// [`notify_one`]: Self::notify_one
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair2 = Arc::clone(&pair);
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// // We notify the condvar that the value has changed.
/// cvar.notify_all();
/// });
///
/// // Wait for the thread to start up.
/// let (lock, cvar) = &*pair;
/// let mut started = lock.lock().unwrap();
/// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
/// while !*started {
/// started = cvar.wait(started).unwrap();
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn notify_all(&self) {
self.inner.notify_all()
}
}
#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for Condvar {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Condvar").finish_non_exhaustive()
}
}
#[stable(feature = "condvar_default", since = "1.10.0")]
impl Default for Condvar {
/// Creates a `Condvar` which is ready to be waited on and notified.
fn default() -> Condvar {
Condvar::new()
}
}