-
Notifications
You must be signed in to change notification settings - Fork 12.7k
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Windows: Implement mutex using futex
Well, the Windows equivalent: `WaitOnAddress`, `WakeByAddressSingle` and `WakeByAddressAll`.
- Loading branch information
1 parent
9e73597
commit 508a095
Showing
16 changed files
with
171 additions
and
104 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
File renamed without changes.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,96 +1,9 @@ | ||
| use crate::sync::atomic::{ | ||
| AtomicU32, | ||
| Ordering::{Acquire, Relaxed, Release}, | ||
| }; | ||
| use crate::sys::futex::{futex_wait, futex_wake}; | ||
|
|
||
| pub struct Mutex { | ||
| /// 0: unlocked | ||
| /// 1: locked, no other threads waiting | ||
| /// 2: locked, and other threads waiting (contended) | ||
| futex: AtomicU32, | ||
| } | ||
|
|
||
| impl Mutex { | ||
| #[inline] | ||
| pub const fn new() -> Self { | ||
| Self { futex: AtomicU32::new(0) } | ||
| } | ||
|
|
||
| #[inline] | ||
| pub fn try_lock(&self) -> bool { | ||
| self.futex.compare_exchange(0, 1, Acquire, Relaxed).is_ok() | ||
| } | ||
|
|
||
| #[inline] | ||
| pub fn lock(&self) { | ||
| if self.futex.compare_exchange(0, 1, Acquire, Relaxed).is_err() { | ||
| self.lock_contended(); | ||
| } | ||
| } | ||
|
|
||
| #[cold] | ||
| fn lock_contended(&self) { | ||
| // Spin first to speed things up if the lock is released quickly. | ||
| let mut state = self.spin(); | ||
|
|
||
| // If it's unlocked now, attempt to take the lock | ||
| // without marking it as contended. | ||
| if state == 0 { | ||
| match self.futex.compare_exchange(0, 1, Acquire, Relaxed) { | ||
| Ok(_) => return, // Locked! | ||
| Err(s) => state = s, | ||
| } | ||
| } | ||
|
|
||
| loop { | ||
| // Put the lock in contended state. | ||
| // We avoid an unnecessary write if it as already set to 2, | ||
| // to be friendlier for the caches. | ||
| if state != 2 && self.futex.swap(2, Acquire) == 0 { | ||
| // We changed it from 0 to 2, so we just successfully locked it. | ||
| return; | ||
| } | ||
|
|
||
| // Wait for the futex to change state, assuming it is still 2. | ||
| futex_wait(&self.futex, 2, None); | ||
|
|
||
| // Spin again after waking up. | ||
| state = self.spin(); | ||
| } | ||
| } | ||
|
|
||
| fn spin(&self) -> u32 { | ||
| let mut spin = 100; | ||
| loop { | ||
| // We only use `load` (and not `swap` or `compare_exchange`) | ||
| // while spinning, to be easier on the caches. | ||
| let state = self.futex.load(Relaxed); | ||
|
|
||
| // We stop spinning when the mutex is unlocked (0), | ||
| // but also when it's contended (2). | ||
| if state != 1 || spin == 0 { | ||
| return state; | ||
| } | ||
|
|
||
| crate::hint::spin_loop(); | ||
| spin -= 1; | ||
| } | ||
| } | ||
|
|
||
| #[inline] | ||
| pub unsafe fn unlock(&self) { | ||
| if self.futex.swap(0, Release) == 2 { | ||
| // We only wake up one thread. When that thread locks the mutex, it | ||
| // will mark the mutex as contended (2) (see lock_contended above), | ||
| // which makes sure that any other waiting threads will also be | ||
| // woken up eventually. | ||
| self.wake(); | ||
| } | ||
| } | ||
|
|
||
| #[cold] | ||
| fn wake(&self) { | ||
| futex_wake(&self.futex); | ||
| cfg_if::cfg_if! { | ||
| if #[cfg(windows)] { | ||
| mod windows; | ||
| pub use windows::*; | ||
| } else { | ||
| mod unix; | ||
| pub use unix::*; | ||
| } | ||
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1 @@ | ||
|
|
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,65 @@ | ||
| use crate::sync::atomic::{ | ||
| AtomicI8, | ||
| Ordering::{Acquire, Relaxed, Release}, | ||
| }; | ||
| use crate::sys::api; | ||
|
|
||
| pub struct Mutex { | ||
| state: AtomicI8, | ||
| } | ||
|
|
||
| const UNLOCKED: i8 = 0; | ||
| const LOCKED: i8 = 1; | ||
| const CONTENDED: i8 = 2; | ||
|
|
||
| impl Mutex { | ||
| #[inline] | ||
| pub const fn new() -> Mutex { | ||
| Mutex { state: AtomicI8::new(UNLOCKED) } | ||
| } | ||
|
|
||
| #[inline] | ||
| pub fn lock(&self) { | ||
| if let Err(state) = self.state.compare_exchange(UNLOCKED, LOCKED, Acquire, Relaxed) { | ||
| self.lock_contended(state) | ||
| } | ||
| } | ||
|
|
||
| #[cold] | ||
| fn lock_contended(&self, mut state: i8) { | ||
| // Note: WaitOnAddress is already quite spin-happy so we don't do any further spinning on top. | ||
| loop { | ||
| // Put the lock in contended state. | ||
| // We avoid an unnecessary write if it as already set to CONTENDED, | ||
| // to be friendlier for the caches. | ||
| if state != CONTENDED && self.state.swap(CONTENDED, Acquire) == UNLOCKED { | ||
| // We changed it from UNLOCKED to CONTENDED, so we just successfully locked it. | ||
| return; | ||
| } | ||
| // Wait for the futex to change state, assuming it is still CONTENDED. | ||
| api::wait_on_address(&self.state, CONTENDED, None); | ||
| state = self.state.load(Relaxed); | ||
| } | ||
| } | ||
|
|
||
| #[inline] | ||
| pub fn try_lock(&self) -> bool { | ||
| self.state.compare_exchange(UNLOCKED, LOCKED, Acquire, Relaxed).is_ok() | ||
| } | ||
|
|
||
| #[inline] | ||
| pub unsafe fn unlock(&self) { | ||
| if self.state.swap(UNLOCKED, Release) == CONTENDED { | ||
| // We only wake up one thread. When that thread locks the mutex, it | ||
| // will mark the mutex as CONTENDED (see lock_contended above), | ||
| // which makes sure that any other waiting threads will also be | ||
| // woken up eventually. | ||
| self.wake(); | ||
| } | ||
| } | ||
|
|
||
| #[cold] | ||
| fn wake(&self) { | ||
| api::wake_by_address_single(&self.state); | ||
| } | ||
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
File renamed without changes.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
File renamed without changes.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters