1use crate::sync::atomic::Ordering::Relaxed;
2use crate::sys::futex::{Futex, futex_wait, futex_wake, futex_wake_all};
3use crate::sys::sync::Mutex;
4use crate::time::Duration;
5
6pub struct Condvar {
7 // The value of this atomic is simply incremented on every notification.
8 // This is used by `.wait()` to not miss any notifications after
9 // unlocking the mutex and before waiting for notifications.
10 futex: Futex,
11}
12
13impl Condvar {
14 #[inline]
15 pub const fn new() -> Self {
16 Self { futex: Futex::new(0) }
17 }
18
19 // All the memory orderings here are `Relaxed`,
20 // because synchronization is done by unlocking and locking the mutex.
21
22 pub fn notify_one(&self) {
23 self.futex.fetch_add(1, Relaxed);
24 futex_wake(&self.futex);
25 }
26
27 pub fn notify_all(&self) {
28 self.futex.fetch_add(1, Relaxed);
29 futex_wake_all(&self.futex);
30 }
31
32 pub unsafe fn wait(&self, mutex: &Mutex) {
33 self.wait_optional_timeout(mutex, None);
34 }
35
36 pub unsafe fn wait_timeout(&self, mutex: &Mutex, timeout: Duration) -> bool {
37 self.wait_optional_timeout(mutex, Some(timeout))
38 }
39
40 unsafe fn wait_optional_timeout(&self, mutex: &Mutex, timeout: Option<Duration>) -> bool {
41 // Examine the notification counter _before_ we unlock the mutex.
42 let futex_value = self.futex.load(Relaxed);
43
44 // Unlock the mutex before going to sleep.
45 mutex.unlock();
46
47 // Wait, but only if there hasn't been any
48 // notification since we unlocked the mutex.
49 let r = futex_wait(&self.futex, futex_value, timeout);
50
51 // Lock the mutex again.
52 mutex.lock();
53
54 r
55 }
56}
57