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std: relax memory orderings in Parker

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Co-authored-by: Tomoaki Kawada <kawada@kmckk.co.jp>
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joboet 2022-06-07 11:06:19 +02:00 committed by joboet
parent b9660de664
commit caff72361f
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GPG Key ID: 704E0149B0194B3C
1 changed files with 7 additions and 8 deletions
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15
library/std/src/sys_common/thread_parker/wait_flag.rs
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@ -25,7 +25,7 @@
use crate::pin::Pin; use crate::pin::Pin;
use crate::sync::atomic::AtomicI8; use crate::sync::atomic::AtomicI8;
use crate::sync::atomic::Ordering::{Relaxed, SeqCst}; use crate::sync::atomic::Ordering::{Acquire, Relaxed, Release};
use crate::sys::wait_flag::WaitFlag; use crate::sys::wait_flag::WaitFlag;
use crate::time::Duration; use crate::time::Duration;
@ -47,7 +47,7 @@ impl Parker {
// This implementation doesn't require `unsafe` and `Pin`, but other implementations do. // This implementation doesn't require `unsafe` and `Pin`, but other implementations do.
pub unsafe fn park(self: Pin<&Self>) { pub unsafe fn park(self: Pin<&Self>) {
match self.state.fetch_sub(1, SeqCst) { match self.state.fetch_sub(1, Acquire) {
// NOTIFIED => EMPTY // NOTIFIED => EMPTY
NOTIFIED => return, NOTIFIED => return,
// EMPTY => PARKED // EMPTY => PARKED
@ -59,7 +59,7 @@ impl Parker {
loop { loop {
self.wait_flag.wait(); self.wait_flag.wait();
match self.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, Relaxed) { match self.state.compare_exchange(NOTIFIED, EMPTY, Acquire, Relaxed) {
Ok(_) => return, Ok(_) => return,
Err(PARKED) => (), Err(PARKED) => (),
Err(_) => panic!("inconsistent park state"), Err(_) => panic!("inconsistent park state"),
@ -69,7 +69,7 @@ impl Parker {
// This implementation doesn't require `unsafe` and `Pin`, but other implementations do. // This implementation doesn't require `unsafe` and `Pin`, but other implementations do.
pub unsafe fn park_timeout(self: Pin<&Self>, dur: Duration) { pub unsafe fn park_timeout(self: Pin<&Self>, dur: Duration) {
match self.state.fetch_sub(1, SeqCst) { match self.state.fetch_sub(1, Acquire) {
NOTIFIED => return, NOTIFIED => return,
EMPTY => (), EMPTY => (),
_ => panic!("inconsistent park state"), _ => panic!("inconsistent park state"),
@ -83,9 +83,8 @@ impl Parker {
// is protected against this by looping until the token is actually given, but // is protected against this by looping until the token is actually given, but
// here we cannot easily tell. // here we cannot easily tell.
// Use `swap` to provide acquire ordering (not strictly necessary, but all other // Use `swap` to provide acquire ordering.
// implementations do). match self.state.swap(EMPTY, Acquire) {
match self.state.swap(EMPTY, SeqCst) {
NOTIFIED => (), NOTIFIED => (),
PARKED => (), PARKED => (),
_ => panic!("inconsistent park state"), _ => panic!("inconsistent park state"),
@ -94,7 +93,7 @@ impl Parker {
// This implementation doesn't require `Pin`, but other implementations do. // This implementation doesn't require `Pin`, but other implementations do.
pub fn unpark(self: Pin<&Self>) { pub fn unpark(self: Pin<&Self>) {
let state = self.state.swap(NOTIFIED, SeqCst); let state = self.state.swap(NOTIFIED, Release);
if state == PARKED { if state == PARKED {
self.wait_flag.raise(); self.wait_flag.raise();