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_value(), 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_value() as u64 {
  17         <libc::time_t>::max_value()
  18     } else {
  19         value as libc::time_t
  20     }
  21 }
  22
  23 impl Condvar {
  24     pub const fn new() -> Condvar {
  25         // Might be moved and address is changing it is better to avoid
  26         // initialization of potentially opaque OS data before it landed
  27         Condvar { inner: UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER) }
  28     }
  29
  30     #[cfg(any(
  31         target_os = "macos",
  32         target_os = "ios",
  33         target_os = "l4re",
  34         target_os = "android",
  35         target_os = "redox"
  36     ))]
  37     pub unsafe fn init(&mut self) {}
  38
  39     #[cfg(not(any(
  40         target_os = "macos",
  41         target_os = "ios",
  42         target_os = "l4re",
  43         target_os = "android",
  44         target_os = "redox"
  45     )))]
  46     pub unsafe fn init(&mut self) {
  47         use crate::mem::MaybeUninit;
  48         let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit();
  49         let r = libc::pthread_condattr_init(attr.as_mut_ptr());
  50         assert_eq!(r, 0);
  51         let r = libc::pthread_condattr_setclock(attr.as_mut_ptr(), libc::CLOCK_MONOTONIC);
  52         assert_eq!(r, 0);
  53         let r = libc::pthread_cond_init(self.inner.get(), attr.as_ptr());
  54         assert_eq!(r, 0);
  55         let r = libc::pthread_condattr_destroy(attr.as_mut_ptr());
  56         assert_eq!(r, 0);
  57     }
  58
  59     #[inline]
  60     pub unsafe fn notify_one(&self) {
  61         let r = libc::pthread_cond_signal(self.inner.get());
  62         debug_assert_eq!(r, 0);
  63     }
  64
  65     #[inline]
  66     pub unsafe fn notify_all(&self) {
  67         let r = libc::pthread_cond_broadcast(self.inner.get());
  68         debug_assert_eq!(r, 0);
  69     }
  70
  71     #[inline]
  72     pub unsafe fn wait(&self, mutex: &Mutex) {
  73         let r = libc::pthread_cond_wait(self.inner.get(), mutex::raw(mutex));
  74         debug_assert_eq!(r, 0);
  75     }
  76
  77     // This implementation is used on systems that support pthread_condattr_setclock
  78     // where we configure condition variable to use monotonic clock (instead of
  79     // default system clock). This approach avoids all problems that result
  80     // from changes made to the system time.
  81     #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "android")))]
  82     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
  83         use crate::mem;
  84
  85         let mut now: libc::timespec = mem::zeroed();
  86         let r = libc::clock_gettime(libc::CLOCK_MONOTONIC, &mut now);
  87         assert_eq!(r, 0);
  88
  89         // Nanosecond calculations can't overflow because both values are below 1e9.
  90         let nsec = dur.subsec_nanos() + now.tv_nsec as u32;
  91
  92         let sec = saturating_cast_to_time_t(dur.as_secs())
  93             .checked_add((nsec / 1_000_000_000) as libc::time_t)
  94             .and_then(|s| s.checked_add(now.tv_sec));
  95         let nsec = nsec % 1_000_000_000;
  96
  97         let timeout =
  98             sec.map(|s| libc::timespec { tv_sec: s, tv_nsec: nsec as _ }).unwrap_or(TIMESPEC_MAX);
  99
 100         let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex), &timeout);
 101         assert!(r == libc::ETIMEDOUT || r == 0);
 102         r == 0
 103     }
 104
 105     // This implementation is modeled after libcxx's condition_variable
 106     // https://github.com/llvm-mirror/libcxx/blob/release_35/src/condition_variable.cpp#L46
 107     // https://github.com/llvm-mirror/libcxx/blob/release_35/include/__mutex_base#L367
 108     #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android"))]
 109     pub unsafe fn wait_timeout(&self, mutex: &Mutex, mut dur: Duration) -> bool {
 110         use crate::ptr;
 111         use crate::time::Instant;
 112
 113         // 1000 years
 114         let max_dur = Duration::from_secs(1000 * 365 * 86400);
 115
 116         if dur > max_dur {
 117             // OSX implementation of `pthread_cond_timedwait` is buggy
 118             // with super long durations. When duration is greater than
 119             // 0x100_0000_0000_0000 seconds, `pthread_cond_timedwait`
 120             // in macOS Sierra return error 316.
 121             //
 122             // This program demonstrates the issue:
 123             // https://gist.github.com/stepancheg/198db4623a20aad2ad7cddb8fda4a63c
 124             //
 125             // To work around this issue, and possible bugs of other OSes, timeout
 126             // is clamped to 1000 years, which is allowable per the API of `wait_timeout`
 127             // because of spurious wakeups.
 128
 129             dur = max_dur;
 130         }
 131
 132         // First, figure out what time it currently is, in both system and
 133         // stable time.  pthread_cond_timedwait uses system time, but we want to
 134         // report timeout based on stable time.
 135         let mut sys_now = libc::timeval { tv_sec: 0, tv_usec: 0 };
 136         let stable_now = Instant::now();
 137         let r = libc::gettimeofday(&mut sys_now, ptr::null_mut());
 138         debug_assert_eq!(r, 0);
 139
 140         let nsec = dur.subsec_nanos() as libc::c_long + (sys_now.tv_usec * 1000) as libc::c_long;
 141         let extra = (nsec / 1_000_000_000) as libc::time_t;
 142         let nsec = nsec % 1_000_000_000;
 143         let seconds = saturating_cast_to_time_t(dur.as_secs());
 144
 145         let timeout = sys_now
 146             .tv_sec
 147             .checked_add(extra)
 148             .and_then(|s| s.checked_add(seconds))
 149             .map(|s| libc::timespec { tv_sec: s, tv_nsec: nsec })
 150             .unwrap_or(TIMESPEC_MAX);
 151
 152         // And wait!
 153         let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex), &timeout);
 154         debug_assert!(r == libc::ETIMEDOUT || r == 0);
 155
 156         // ETIMEDOUT is not a totally reliable method of determining timeout due
 157         // to clock shifts, so do the check ourselves
 158         stable_now.elapsed() < dur
 159     }
 160
 161     #[inline]
 162     #[cfg(not(target_os = "dragonfly"))]
 163     pub unsafe fn destroy(&self) {
 164         let r = libc::pthread_cond_destroy(self.inner.get());
 165         debug_assert_eq!(r, 0);
 166     }
 167
 168     #[inline]
 169     #[cfg(target_os = "dragonfly")]
 170     pub unsafe fn destroy(&self) {
 171         let r = libc::pthread_cond_destroy(self.inner.get());
 172         // On DragonFly pthread_cond_destroy() returns EINVAL if called on
 173         // a condvar that was just initialized with
 174         // libc::PTHREAD_COND_INITIALIZER. Once it is used or
 175         // pthread_cond_init() is called, this behaviour no longer occurs.
 176         debug_assert!(r == 0 || r == libc::EINVAL);
 177     }
 178 }