diff options
Diffstat (limited to 'library/std/src/sys/unix/condvar.rs')
| -rw-r--r-- | library/std/src/sys/unix/condvar.rs | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/library/std/src/sys/unix/condvar.rs b/library/std/src/sys/unix/condvar.rs new file mode 100644 index 00000000000..9f1847943f3 --- /dev/null +++ b/library/std/src/sys/unix/condvar.rs @@ -0,0 +1,174 @@ +use crate::cell::UnsafeCell; +use crate::sys::mutex::{self, Mutex}; +use crate::time::Duration; + +pub struct Condvar { + inner: UnsafeCell<libc::pthread_cond_t>, +} + +unsafe impl Send for Condvar {} +unsafe impl Sync for Condvar {} + +const TIMESPEC_MAX: libc::timespec = + libc::timespec { tv_sec: <libc::time_t>::MAX, tv_nsec: 1_000_000_000 - 1 }; + +fn saturating_cast_to_time_t(value: u64) -> libc::time_t { + if value > <libc::time_t>::MAX as u64 { <libc::time_t>::MAX } else { value as libc::time_t } +} + +impl Condvar { + pub const fn new() -> Condvar { + // Might be moved and address is changing it is better to avoid + // initialization of potentially opaque OS data before it landed + Condvar { inner: UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER) } + } + + #[cfg(any( + target_os = "macos", + target_os = "ios", + target_os = "l4re", + target_os = "android", + target_os = "redox" + ))] + pub unsafe fn init(&mut self) {} + + #[cfg(not(any( + target_os = "macos", + target_os = "ios", + target_os = "l4re", + target_os = "android", + target_os = "redox" + )))] + pub unsafe fn init(&mut self) { + use crate::mem::MaybeUninit; + let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit(); + let r = libc::pthread_condattr_init(attr.as_mut_ptr()); + assert_eq!(r, 0); + let r = libc::pthread_condattr_setclock(attr.as_mut_ptr(), libc::CLOCK_MONOTONIC); + assert_eq!(r, 0); + let r = libc::pthread_cond_init(self.inner.get(), attr.as_ptr()); + assert_eq!(r, 0); + let r = libc::pthread_condattr_destroy(attr.as_mut_ptr()); + assert_eq!(r, 0); + } + + #[inline] + pub unsafe fn notify_one(&self) { + let r = libc::pthread_cond_signal(self.inner.get()); + debug_assert_eq!(r, 0); + } + + #[inline] + pub unsafe fn notify_all(&self) { + let r = libc::pthread_cond_broadcast(self.inner.get()); + debug_assert_eq!(r, 0); + } + + #[inline] + pub unsafe fn wait(&self, mutex: &Mutex) { + let r = libc::pthread_cond_wait(self.inner.get(), mutex::raw(mutex)); + debug_assert_eq!(r, 0); + } + + // This implementation is used on systems that support pthread_condattr_setclock + // where we configure condition variable to use monotonic clock (instead of + // default system clock). This approach avoids all problems that result + // from changes made to the system time. + #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "android")))] + pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool { + use crate::mem; + + let mut now: libc::timespec = mem::zeroed(); + let r = libc::clock_gettime(libc::CLOCK_MONOTONIC, &mut now); + assert_eq!(r, 0); + + // Nanosecond calculations can't overflow because both values are below 1e9. + let nsec = dur.subsec_nanos() + now.tv_nsec as u32; + + let sec = saturating_cast_to_time_t(dur.as_secs()) + .checked_add((nsec / 1_000_000_000) as libc::time_t) + .and_then(|s| s.checked_add(now.tv_sec)); + let nsec = nsec % 1_000_000_000; + + let timeout = + sec.map(|s| libc::timespec { tv_sec: s, tv_nsec: nsec as _ }).unwrap_or(TIMESPEC_MAX); + + let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex), &timeout); + assert!(r == libc::ETIMEDOUT || r == 0); + r == 0 + } + + // This implementation is modeled after libcxx's condition_variable + // https://github.com/llvm-mirror/libcxx/blob/release_35/src/condition_variable.cpp#L46 + // https://github.com/llvm-mirror/libcxx/blob/release_35/include/__mutex_base#L367 + #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android"))] + pub unsafe fn wait_timeout(&self, mutex: &Mutex, mut dur: Duration) -> bool { + use crate::ptr; + use crate::time::Instant; + + // 1000 years + let max_dur = Duration::from_secs(1000 * 365 * 86400); + + if dur > max_dur { + // OSX implementation of `pthread_cond_timedwait` is buggy + // with super long durations. When duration is greater than + // 0x100_0000_0000_0000 seconds, `pthread_cond_timedwait` + // in macOS Sierra return error 316. + // + // This program demonstrates the issue: + // https://gist.github.com/stepancheg/198db4623a20aad2ad7cddb8fda4a63c + // + // To work around this issue, and possible bugs of other OSes, timeout + // is clamped to 1000 years, which is allowable per the API of `wait_timeout` + // because of spurious wakeups. + + dur = max_dur; + } + + // First, figure out what time it currently is, in both system and + // stable time. pthread_cond_timedwait uses system time, but we want to + // report timeout based on stable time. + let mut sys_now = libc::timeval { tv_sec: 0, tv_usec: 0 }; + let stable_now = Instant::now(); + let r = libc::gettimeofday(&mut sys_now, ptr::null_mut()); + debug_assert_eq!(r, 0); + + let nsec = dur.subsec_nanos() as libc::c_long + (sys_now.tv_usec * 1000) as libc::c_long; + let extra = (nsec / 1_000_000_000) as libc::time_t; + let nsec = nsec % 1_000_000_000; + let seconds = saturating_cast_to_time_t(dur.as_secs()); + + let timeout = sys_now + .tv_sec + .checked_add(extra) + .and_then(|s| s.checked_add(seconds)) + .map(|s| libc::timespec { tv_sec: s, tv_nsec: nsec }) + .unwrap_or(TIMESPEC_MAX); + + // And wait! + let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex), &timeout); + debug_assert!(r == libc::ETIMEDOUT || r == 0); + + // ETIMEDOUT is not a totally reliable method of determining timeout due + // to clock shifts, so do the check ourselves + stable_now.elapsed() < dur + } + + #[inline] + #[cfg(not(target_os = "dragonfly"))] + pub unsafe fn destroy(&self) { + let r = libc::pthread_cond_destroy(self.inner.get()); + debug_assert_eq!(r, 0); + } + + #[inline] + #[cfg(target_os = "dragonfly")] + pub unsafe fn destroy(&self) { + let r = libc::pthread_cond_destroy(self.inner.get()); + // On DragonFly pthread_cond_destroy() returns EINVAL if called on + // a condvar that was just initialized with + // libc::PTHREAD_COND_INITIALIZER. Once it is used or + // pthread_cond_init() is called, this behaviour no longer occurs. + debug_assert!(r == 0 || r == libc::EINVAL); + } +} |