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Auto merge of #67076 - mbrubeck:condvar, r=dtolnay 

Stabilize Condvar::wait_while and wait_timeout_while (previously wait_until, wait_timeout_until)

Closes #47960.
This commit is contained in:
bors 2020-01-14 10:34:43 +00:00
parent c06e4aca19 98d054af08
commit cb6122db3f
1 changed files with 34 additions and 43 deletions
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77
src/libstd/sync/condvar.rs
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@ -204,9 +204,7 @@ impl Condvar {
}
/// Blocks the current thread until this condition variable receives a
/// notification and the required condition is met. Spurious wakeups are
/// ignored and this function will only return once the condition has been
/// met.
/// 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
@ -228,29 +226,27 @@ impl Condvar {
/// # Examples
///
/// ```
/// #![feature(wait_until)]
///
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair = Arc::new((Mutex::new(true), Condvar::new()));
/// let pair2 = pair.clone();
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// 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 `false`, we wait.
/// let _guard = cvar.wait_until(lock.lock().unwrap(), |started| { *started }).unwrap();
/// // As long as the value inside the `Mutex<bool>` is `true`, we wait.
/// let _guard = cvar.wait_while(lock.lock().unwrap(), |pending| { *pending }).unwrap();
/// ```
#[unstable(feature = "wait_until", issue = "47960")]
pub fn wait_until<'a, T, F>(
#[stable(feature = "wait_until", since = "1.42.0")]
pub fn wait_while<'a, T, F>(
&self,
mut guard: MutexGuard<'a, T>,
mut condition: F,
@ -258,7 +254,7 @@ impl Condvar {
where
F: FnMut(&mut T) -> bool,
{
while !condition(&mut *guard) {
while condition(&mut *guard) {
guard = self.wait(guard)?;
}
Ok(guard)
@ -343,11 +339,10 @@ impl Condvar {
/// 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 time-out to not exceed some duration in
/// 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_until` method
/// to wait until a condition is met with a total time-out regardless
/// of spurious wakes.
/// 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.
@ -356,7 +351,7 @@ impl Condvar {
/// returns, regardless of whether the timeout elapsed or not.
///
/// [`wait`]: #method.wait
/// [`wait_timeout_until`]: #method.wait_timeout_until
/// [`wait_timeout_while`]: #method.wait_timeout_while
/// [`WaitTimeoutResult`]: struct.WaitTimeoutResult.html
///
/// # Examples
@ -407,10 +402,9 @@ impl Condvar {
}
/// Waits on this condition variable for a notification, timing out after a
/// specified duration. Spurious wakes will not cause this function to
/// return.
/// specified duration.
///
/// The semantics of this function are equivalent to [`wait_until`] except
/// 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 may not cause the maximum
@ -423,47 +417,45 @@ impl Condvar {
/// The returned [`WaitTimeoutResult`] value indicates if the timeout is
/// known to have elapsed without the condition being met.
///
/// Like [`wait_until`], the lock specified will be re-acquired when this
/// Like [`wait_while`], the lock specified will be re-acquired when this
/// function returns, regardless of whether the timeout elapsed or not.
///
/// [`wait_until`]: #method.wait_until
/// [`wait_while`]: #method.wait_while
/// [`wait_timeout`]: #method.wait_timeout
/// [`WaitTimeoutResult`]: struct.WaitTimeoutResult.html
///
/// # Examples
///
/// ```
/// #![feature(wait_timeout_until)]
///
/// use std::sync::{Arc, Mutex, Condvar};
/// use std::thread;
/// use std::time::Duration;
///
/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
/// let pair = Arc::new((Mutex::new(true), Condvar::new()));
/// let pair2 = pair.clone();
///
/// thread::spawn(move|| {
/// let (lock, cvar) = &*pair2;
/// let mut started = lock.lock().unwrap();
/// *started = true;
/// 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_until(
/// let result = cvar.wait_timeout_while(
/// lock.lock().unwrap(),
/// Duration::from_millis(100),
/// |&mut started| started,
/// |&mut pending| pending,
/// ).unwrap();
/// if result.1.timed_out() {
/// // timed-out without the condition ever evaluating to true.
/// // timed-out without the condition ever evaluating to false.
/// }
/// // access the locked mutex via result.0
/// ```
#[unstable(feature = "wait_timeout_until", issue = "47960")]
pub fn wait_timeout_until<'a, T, F>(
#[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,
@ -474,7 +466,7 @@ impl Condvar {
{
let start = Instant::now();
loop {
if condition(&mut *guard) {
if !condition(&mut *guard) {
return Ok((guard, WaitTimeoutResult(false)));
}
let timeout = match dur.checked_sub(start.elapsed()) {
@ -613,7 +605,6 @@ impl Drop for Condvar {
#[cfg(test)]
mod tests {
use crate::sync::atomic::{AtomicBool, Ordering};
/// #![feature(wait_until)]
use crate::sync::mpsc::channel;
use crate::sync::{Arc, Condvar, Mutex};
use crate::thread;
@ -683,7 +674,7 @@ mod tests {
#[test]
#[cfg_attr(target_os = "emscripten", ignore)]
fn wait_until() {
fn wait_while() {
let pair = Arc::new((Mutex::new(false), Condvar::new()));
let pair2 = pair.clone();
@ -698,7 +689,7 @@ mod tests {
// Wait for the thread to start up.
let &(ref lock, ref cvar) = &*pair;
let guard = cvar.wait_until(lock.lock().unwrap(), |started| *started);
let guard = cvar.wait_while(lock.lock().unwrap(), |started| !*started);
assert!(*guard.unwrap());
}
@ -725,24 +716,24 @@ mod tests {
#[test]
#[cfg_attr(target_os = "emscripten", ignore)]
#[cfg_attr(target_env = "sgx", ignore)] // FIXME: https://github.com/fortanix/rust-sgx/issues/31
fn wait_timeout_until_wait() {
fn wait_timeout_while_wait() {
let m = Arc::new(Mutex::new(()));
let c = Arc::new(Condvar::new());
let g = m.lock().unwrap();
let (_g, wait) = c.wait_timeout_until(g, Duration::from_millis(1), |_| false).unwrap();
let (_g, wait) = c.wait_timeout_while(g, Duration::from_millis(1), |_| true).unwrap();
// no spurious wakeups. ensure it timed-out
assert!(wait.timed_out());
}
#[test]
#[cfg_attr(target_os = "emscripten", ignore)]
fn wait_timeout_until_instant_satisfy() {
fn wait_timeout_while_instant_satisfy() {
let m = Arc::new(Mutex::new(()));
let c = Arc::new(Condvar::new());
let g = m.lock().unwrap();
let (_g, wait) = c.wait_timeout_until(g, Duration::from_millis(0), |_| true).unwrap();
let (_g, wait) = c.wait_timeout_while(g, Duration::from_millis(0), |_| false).unwrap();
// ensure it didn't time-out even if we were not given any time.
assert!(!wait.timed_out());
}
@ -750,7 +741,7 @@ mod tests {
#[test]
#[cfg_attr(target_os = "emscripten", ignore)]
#[cfg_attr(target_env = "sgx", ignore)] // FIXME: https://github.com/fortanix/rust-sgx/issues/31
fn wait_timeout_until_wake() {
fn wait_timeout_while_wake() {
let pair = Arc::new((Mutex::new(false), Condvar::new()));
let pair_copy = pair.clone();
@ -764,7 +755,7 @@ mod tests {
cvar.notify_one();
});
let (g2, wait) = c
.wait_timeout_until(g, Duration::from_millis(u64::MAX), |&mut notified| notified)
.wait_timeout_while(g, Duration::from_millis(u64::MAX), |&mut notified| !notified)
.unwrap();
// ensure it didn't time-out even if we were not given any time.
assert!(!wait.timed_out());