src/libstd/sys/unix/condvar.rs

   1 use crate::cell::UnsafeCell;
   2 use crate::sys::mutex::{self, Mutex};
   3 use crate::time::Duration;
   4
   5 pub struct Condvar {
   6     inner: UnsafeCell<libc::pthread_cond_t>,
   7 }
   8
   9 unsafe impl Send for Condvar {}
  10 unsafe impl Sync for Condvar {}
  11
  12 const TIMESPEC_MAX: libc::timespec =
  13     libc::timespec { tv_sec: <libc::time_t>::MAX, tv_nsec: 1_000_000_000 - 1 };
  14
  15 fn saturating_cast_to_time_t(value: u64) -> libc::time_t {
  16     if value > <libc::time_t>::MAX as u64 { <libc::time_t>::MAX } else { value as libc::time_t }
  17 }
  18
  19 impl Condvar {
  20     pub const fn new() -> Condvar {
  21         // Might be moved and address is changing it is better to avoid
  22         // initialization of potentially opaque OS data before it landed
  23         Condvar { inner: UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER) }
  24     }
  25
  26     #[cfg(any(
  27         target_os = "macos",
  28         target_os = "ios",
  29         target_os = "l4re",
  30         target_os = "android",
  31         target_os = "redox"
  32     ))]
  33     pub unsafe fn init(&mut self) {}
  34
  35     #[cfg(not(any(
  36         target_os = "macos",
  37         target_os = "ios",
  38         target_os = "l4re",
  39         target_os = "android",
  40         target_os = "redox"
  41     )))]
  42     pub unsafe fn init(&mut self) {
  43         use crate::mem::MaybeUninit;
  44         let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit();
  45         let r = libc::pthread_condattr_init(attr.as_mut_ptr());
  46         assert_eq!(r, 0);
  47         let r = libc::pthread_condattr_setclock(attr.as_mut_ptr(), libc::CLOCK_MONOTONIC);
  48         assert_eq!(r, 0);
  49         let r = libc::pthread_cond_init(self.inner.get(), attr.as_ptr());
  50         assert_eq!(r, 0);
  51         let r = libc::pthread_condattr_destroy(attr.as_mut_ptr());
  52         assert_eq!(r, 0);
  53     }
  54
  55     #[inline]
  56     pub unsafe fn notify_one(&self) {
  57         let r = libc::pthread_cond_signal(self.inner.get());
  58         debug_assert_eq!(r, 0);
  59     }
  60
  61     #[inline]
  62     pub unsafe fn notify_all(&self) {
  63         let r = libc::pthread_cond_broadcast(self.inner.get());
  64         debug_assert_eq!(r, 0);
  65     }
  66
  67     #[inline]
  68     pub unsafe fn wait(&self, mutex: &Mutex) {
  69         let r = libc::pthread_cond_wait(self.inner.get(), mutex::raw(mutex));
  70         debug_assert_eq!(r, 0);
  71     }
  72
  73     // This implementation is used on systems that support pthread_condattr_setclock
  74     // where we configure condition variable to use monotonic clock (instead of
  75     // default system clock). This approach avoids all problems that result
  76     // from changes made to the system time.
  77     #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "android")))]
  78     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
  79         use crate::mem;
  80
  81         let mut now: libc::timespec = mem::zeroed();
  82         let r = libc::clock_gettime(libc::CLOCK_MONOTONIC, &mut now);
  83         assert_eq!(r, 0);
  84
  85         // Nanosecond calculations can't overflow because both values are below 1e9.
  86         let nsec = dur.subsec_nanos() + now.tv_nsec as u32;
  87
  88         let sec = saturating_cast_to_time_t(dur.as_secs())
  89             .checked_add((nsec / 1_000_000_000) as libc::time_t)
  90             .and_then(|s| s.checked_add(now.tv_sec));
  91         let nsec = nsec % 1_000_000_000;
  92
  93         let timeout =
  94             sec.map(|s| libc::timespec { tv_sec: s, tv_nsec: nsec as _ }).unwrap_or(TIMESPEC_MAX);
  95
  96         let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex), &timeout);
  97         assert!(r == libc::ETIMEDOUT || r == 0);
  98         r == 0
  99     }
 100
 101     // This implementation is modeled after libcxx's condition_variable
 102     // https://github.com/llvm-mirror/libcxx/blob/release_35/src/condition_variable.cpp#L46
 103     // https://github.com/llvm-mirror/libcxx/blob/release_35/include/__mutex_base#L367
 104     #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android"))]
 105     pub unsafe fn wait_timeout(&self, mutex: &Mutex, mut dur: Duration) -> bool {
 106         use crate::ptr;
 107         use crate::time::Instant;
 108
 109         // 1000 years
 110         let max_dur = Duration::from_secs(1000 * 365 * 86400);
 111
 112         if dur > max_dur {
 113             // OSX implementation of `pthread_cond_timedwait` is buggy
 114             // with super long durations. When duration is greater than
 115             // 0x100_0000_0000_0000 seconds, `pthread_cond_timedwait`
 116             // in macOS Sierra return error 316.
 117             //
 118             // This program demonstrates the issue:
 119             // https://gist.github.com/stepancheg/198db4623a20aad2ad7cddb8fda4a63c
 120             //
 121             // To work around this issue, and possible bugs of other OSes, timeout
 122             // is clamped to 1000 years, which is allowable per the API of `wait_timeout`
 123             // because of spurious wakeups.
 124
 125             dur = max_dur;
 126         }
 127
 128         // First, figure out what time it currently is, in both system and
 129         // stable time.  pthread_cond_timedwait uses system time, but we want to
 130         // report timeout based on stable time.
 131         let mut sys_now = libc::timeval { tv_sec: 0, tv_usec: 0 };
 132         let stable_now = Instant::now();
 133         let r = libc::gettimeofday(&mut sys_now, ptr::null_mut());
 134         debug_assert_eq!(r, 0);
 135
 136         let nsec = dur.subsec_nanos() as libc::c_long + (sys_now.tv_usec * 1000) as libc::c_long;
 137         let extra = (nsec / 1_000_000_000) as libc::time_t;
 138         let nsec = nsec % 1_000_000_000;
 139         let seconds = saturating_cast_to_time_t(dur.as_secs());
 140
 141         let timeout = sys_now
 142             .tv_sec
 143             .checked_add(extra)
 144             .and_then(|s| s.checked_add(seconds))
 145             .map(|s| libc::timespec { tv_sec: s, tv_nsec: nsec })
 146             .unwrap_or(TIMESPEC_MAX);
 147
 148         // And wait!
 149         let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex), &timeout);
 150         debug_assert!(r == libc::ETIMEDOUT || r == 0);
 151
 152         // ETIMEDOUT is not a totally reliable method of determining timeout due
 153         // to clock shifts, so do the check ourselves
 154         stable_now.elapsed() < dur
 155     }
 156
 157     #[inline]
 158     #[cfg(not(target_os = "dragonfly"))]
 159     pub unsafe fn destroy(&self) {
 160         let r = libc::pthread_cond_destroy(self.inner.get());
 161         debug_assert_eq!(r, 0);
 162     }
 163
 164     #[inline]
 165     #[cfg(target_os = "dragonfly")]
 166     pub unsafe fn destroy(&self) {
 167         let r = libc::pthread_cond_destroy(self.inner.get());
 168         // On DragonFly pthread_cond_destroy() returns EINVAL if called on
 169         // a condvar that was just initialized with
 170         // libc::PTHREAD_COND_INITIALIZER. Once it is used or
 171         // pthread_cond_init() is called, this behaviour no longer occurs.
 172         debug_assert!(r == 0 || r == libc::EINVAL);
 173     }
 174 }