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// Copyright 2016 Amanieu d'Antras
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// copied, modified, or distributed except according to those terms.
use core::{
ptr,
sync::atomic::{AtomicI32, Ordering},
};
use std::thread;
use std::time::Instant;
use syscall::{
call::futex,
data::TimeSpec,
error::{Error, EAGAIN, EFAULT, EINTR, ETIMEDOUT},
flag::{FUTEX_WAIT, FUTEX_WAKE},
};
const UNPARKED: i32 = 0;
const PARKED: i32 = 1;
// Helper type for putting a thread to sleep until some other thread wakes it up
pub struct ThreadParker {
futex: AtomicI32,
}
impl super::ThreadParkerT for ThreadParker {
type UnparkHandle = UnparkHandle;
const IS_CHEAP_TO_CONSTRUCT: bool = true;
#[inline]
fn new() -> ThreadParker {
ThreadParker {
futex: AtomicI32::new(UNPARKED),
}
}
#[inline]
unsafe fn prepare_park(&self) {
self.futex.store(PARKED, Ordering::Relaxed);
}
#[inline]
unsafe fn timed_out(&self) -> bool {
self.futex.load(Ordering::Relaxed) != UNPARKED
}
#[inline]
unsafe fn park(&self) {
while self.futex.load(Ordering::Acquire) != UNPARKED {
self.futex_wait(None);
}
}
#[inline]
unsafe fn park_until(&self, timeout: Instant) -> bool {
while self.futex.load(Ordering::Acquire) != UNPARKED {
let now = Instant::now();
if timeout <= now {
return false;
}
let diff = timeout - now;
if diff.as_secs() > i64::max_value() as u64 {
// Timeout overflowed, just sleep indefinitely
self.park();
return true;
}
let ts = TimeSpec {
tv_sec: diff.as_secs() as i64,
tv_nsec: diff.subsec_nanos() as i32,
};
self.futex_wait(Some(ts));
}
true
}
#[inline]
unsafe fn unpark_lock(&self) -> UnparkHandle {
// We don't need to lock anything, just clear the state
self.futex.store(UNPARKED, Ordering::Release);
UnparkHandle { futex: self.ptr() }
}
}
impl ThreadParker {
#[inline]
fn futex_wait(&self, ts: Option<TimeSpec>) {
let ts_ptr = ts
.as_ref()
.map(|ts_ref| ts_ref as *const _)
.unwrap_or(ptr::null());
let r = unsafe {
futex(
self.ptr(),
FUTEX_WAIT,
PARKED,
ts_ptr as usize,
ptr::null_mut(),
)
};
match r {
Ok(r) => debug_assert_eq!(r, 0),
Err(Error { errno }) => {
debug_assert!(errno == EINTR || errno == EAGAIN || errno == ETIMEDOUT);
}
}
}
#[inline]
fn ptr(&self) -> *mut i32 {
&self.futex as *const AtomicI32 as *mut i32
}
}
pub struct UnparkHandle {
futex: *mut i32,
}
impl super::UnparkHandleT for UnparkHandle {
#[inline]
unsafe fn unpark(self) {
// The thread data may have been freed at this point, but it doesn't
// matter since the syscall will just return EFAULT in that case.
let r = futex(self.futex, FUTEX_WAKE, PARKED, 0, ptr::null_mut());
match r {
Ok(num_woken) => debug_assert!(num_woken == 0 || num_woken == 1),
Err(Error { errno }) => debug_assert_eq!(errno, EFAULT),
}
}
}
#[inline]
pub fn thread_yield() {
thread::yield_now();
}