Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Cleanup timeouts in pthread condvar #103146

Merged
merged 1 commit into from
Dec 11, 2022
Merged

Cleanup timeouts in pthread condvar #103146

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
93 changes: 30 additions & 63 deletions library/std/src/sys/unix/locks/pthread_condvar.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ use crate::cell::UnsafeCell;
use crate::ptr;
use crate::sync::atomic::{AtomicPtr, Ordering::Relaxed};
use crate::sys::locks::{pthread_mutex, Mutex};
use crate::sys::time::TIMESPEC_MAX;
use crate::sys_common::lazy_box::{LazyBox, LazyInit};
use crate::time::Duration;

Expand All @@ -12,13 +13,6 @@ pub struct Condvar {
mutex: AtomicPtr<libc::pthread_mutex_t>,
}

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 }
}

#[inline]
fn raw(c: &Condvar) -> *mut libc::pthread_cond_t {
c.inner.0.get()
Expand Down Expand Up @@ -133,26 +127,15 @@ impl Condvar {
target_os = "horizon"
)))]
pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
use crate::mem;
use crate::sys::time::Timespec;

let mutex = pthread_mutex::raw(mutex);
self.verify(mutex);

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 timeout = Timespec::now(libc::CLOCK_MONOTONIC)
.checked_add_duration(&dur)
.and_then(|t| t.to_timespec())
.unwrap_or(TIMESPEC_MAX);
let r = libc::pthread_cond_timedwait(raw(self), mutex, &timeout);
assert!(r == libc::ETIMEDOUT || r == 0);
r == 0
Expand All @@ -169,57 +152,41 @@ impl Condvar {
target_os = "espidf",
target_os = "horizon"
))]
pub unsafe fn wait_timeout(&self, mutex: &Mutex, mut dur: Duration) -> bool {
pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
use crate::sys::time::SystemTime;
use crate::time::Instant;

let mutex = pthread_mutex::raw(mutex);
self.verify(mutex);

// 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());
assert_eq!(r, 0, "unexpected error: {:?}", crate::io::Error::last_os_error());

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 })
// 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 returns 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.
let dur = Duration::min(dur, Duration::from_secs(1000 * 365 * 86400));

// pthread_cond_timedwait uses system time, but we want to report timeout
// based on stable time.
let now = Instant::now();

let timeout = SystemTime::now()
.t
.checked_add_duration(&dur)
.and_then(|t| t.to_timespec())
.unwrap_or(TIMESPEC_MAX);

// And wait!
let r = libc::pthread_cond_timedwait(raw(self), 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
now.elapsed() < dur
}
}
4 changes: 1 addition & 3 deletions library/std/src/sys/unix/thread_parker/pthread.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ use crate::pin::Pin;
use crate::ptr::addr_of_mut;
use crate::sync::atomic::AtomicUsize;
use crate::sync::atomic::Ordering::SeqCst;
use crate::sys::time::TIMESPEC_MAX;
use crate::time::Duration;

const EMPTY: usize = 0;
Expand All @@ -32,9 +33,6 @@ unsafe fn wait(cond: *mut libc::pthread_cond_t, lock: *mut libc::pthread_mutex_t
debug_assert_eq!(r, 0);
}

const TIMESPEC_MAX: libc::timespec =
libc::timespec { tv_sec: <libc::time_t>::MAX, tv_nsec: 1_000_000_000 - 1 };

unsafe fn wait_timeout(
cond: *mut libc::pthread_cond_t,
lock: *mut libc::pthread_mutex_t,
Expand Down
3 changes: 3 additions & 0 deletions library/std/src/sys/unix/time.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,9 @@ pub use self::inner::Instant;

const NSEC_PER_SEC: u64 = 1_000_000_000;
pub const UNIX_EPOCH: SystemTime = SystemTime { t: Timespec::zero() };
#[allow(dead_code)] // Used for pthread condvar timeouts
pub const TIMESPEC_MAX: libc::timespec =
libc::timespec { tv_sec: <libc::time_t>::MAX, tv_nsec: 1_000_000_000 - 1 };

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
Expand Down