mirror of
https://github.com/ziglang/zig.git
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Merge pull request #3918 from kprotty/lock_fix
Synchronization primitive improvements
This commit is contained in:
Andrew Kelley
GitHub
commit
4d54e9a4fb
@ -1,12 +1,13 @@
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const std = @import("std.zig");
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const builtin = @import("builtin");
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const os = std.os;
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const testing = std.testing;
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const SpinLock = std.SpinLock;
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const ResetEvent = std.ResetEvent;
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/// Lock may be held only once. If the same thread
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/// tries to acquire the same mutex twice, it deadlocks.
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/// This type supports static initialization and is based off of Webkit's WTF Lock (via rust parking_lot)
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/// https://github.com/Amanieu/parking_lot/blob/master/core/src/word_lock.rs
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/// This type supports static initialization and is at most `@sizeOf(usize)` in size.
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/// When an application is built in single threaded release mode, all the functions are
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/// no-ops. In single threaded debug mode, there is deadlock detection.
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pub const Mutex = if (builtin.single_threaded)
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@ -24,35 +25,114 @@ pub const Mutex = if (builtin.single_threaded)
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}
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}
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};
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pub fn init() Mutex {
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return Mutex{ .lock = lock_init };
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}
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pub fn deinit(self: *Mutex) void {}
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pub fn acquire(self: *Mutex) Held {
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if (std.debug.runtime_safety and self.lock) {
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@panic("deadlock detected");
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pub fn deinit(self: *Mutex) void {
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self.* = undefined;
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}
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pub fn tryAcquire(self: *Mutex) ?Held {
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if (std.debug.runtime_safety) {
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if (self.lock) return null;
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self.lock = true;
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}
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return Held{ .mutex = self };
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}
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pub fn acquire(self: *Mutex) Held {
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return self.tryAcquire() orelse @panic("deadlock detected");
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}
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}
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else
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else if (builtin.os == .windows)
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// https://locklessinc.com/articles/keyed_events/
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extern union {
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locked: u8,
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waiters: u32,
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const WAKE = 1 << 8;
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const WAIT = 1 << 9;
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pub fn init() Mutex {
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return Mutex{ .waiters = 0 };
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}
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pub fn deinit(self: *Mutex) void {
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self.* = undefined;
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}
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pub fn tryAcquire(self: *Mutex) ?Held {
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if (@atomicRmw(u8, &self.locked, .Xchg, 1, .Acquire) != 0)
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return null;
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return Held{ .mutex = self };
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}
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pub fn acquire(self: *Mutex) Held {
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return self.tryAcquire() orelse self.acquireSlow();
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}
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fn acquireSlow(self: *Mutex) Held {
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@setCold(true);
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while (true) : (SpinLock.loopHint(1)) {
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const waiters = @atomicLoad(u32, &self.waiters, .Monotonic);
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// try and take lock if unlocked
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if ((waiters & 1) == 0) {
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if (@atomicRmw(u8, &self.locked, .Xchg, 1, .Acquire) == 0)
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return Held{ .mutex = self };
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// otherwise, try and update the waiting count.
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// then unset the WAKE bit so that another unlocker can wake up a thread.
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} else if (@cmpxchgWeak(u32, &self.waiters, waiters, (waiters + WAIT) | 1, .Monotonic, .Monotonic) == null) {
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ResetEvent.OsEvent.Futex.wait(@ptrCast(*i32, &self.waiters), undefined, null) catch unreachable;
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_ = @atomicRmw(u32, &self.waiters, .Sub, WAKE, .Monotonic);
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}
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}
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}
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pub const Held = struct {
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mutex: *Mutex,
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pub fn release(self: Held) void {
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// unlock without a rmw/cmpxchg instruction
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@atomicStore(u8, @ptrCast(*u8, &self.mutex.locked), 0, .Release);
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while (true) : (SpinLock.loopHint(1)) {
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const waiters = @atomicLoad(u32, &self.mutex.waiters, .Monotonic);
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// no one is waiting
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if (waiters < WAIT) return;
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// someone grabbed the lock and will do the wake instead
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if (waiters & 1 != 0) return;
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// someone else is currently waking up
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if (waiters & WAKE != 0) return;
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// try to decrease the waiter count & set the WAKE bit meaning a thread is waking up
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if (@cmpxchgWeak(u32, &self.mutex.waiters, waiters, waiters - WAIT + WAKE, .Release, .Monotonic) == null)
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return ResetEvent.OsEvent.Futex.wake(@ptrCast(*i32, &self.mutex.waiters));
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}
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}
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};
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}
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else if (builtin.link_libc or builtin.os == .linux)
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// stack-based version of https://github.com/Amanieu/parking_lot/blob/master/core/src/word_lock.rs
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struct {
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state: usize,
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/// number of times to spin trying to acquire the lock.
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/// https://webkit.org/blog/6161/locking-in-webkit/
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const SPIN_COUNT = 40;
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const MUTEX_LOCK: usize = 1 << 0;
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const QUEUE_LOCK: usize = 1 << 1;
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const QUEUE_MASK: usize = ~(MUTEX_LOCK | QUEUE_LOCK);
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const QueueNode = std.atomic.Stack(ResetEvent).Node;
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/// number of iterations to spin yielding the cpu
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const SPIN_CPU = 4;
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/// number of iterations to spin in the cpu yield loop
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const SPIN_CPU_COUNT = 30;
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/// number of iterations to spin yielding the thread
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const SPIN_THREAD = 1;
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const Node = struct {
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next: ?*Node,
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event: ResetEvent,
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};
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pub fn init() Mutex {
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return Mutex{ .state = 0 };
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@ -62,98 +142,112 @@ else
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self.* = undefined;
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}
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pub fn tryAcquire(self: *Mutex) ?Held {
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if (@cmpxchgWeak(usize, &self.state, 0, MUTEX_LOCK, .Acquire, .Monotonic) != null)
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return null;
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return Held{ .mutex = self };
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}
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pub fn acquire(self: *Mutex) Held {
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return self.tryAcquire() orelse {
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self.acquireSlow();
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return Held{ .mutex = self };
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};
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}
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fn acquireSlow(self: *Mutex) void {
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// inlining the fast path and hiding *Slow()
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// calls behind a @setCold(true) appears to
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// improve performance in release builds.
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@setCold(true);
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while (true) {
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// try and spin for a bit to acquire the mutex if theres currently no queue
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var spin_count: u32 = SPIN_COUNT;
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var state = @atomicLoad(usize, &self.state, .Monotonic);
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while (spin_count != 0) : (spin_count -= 1) {
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if (state & MUTEX_LOCK == 0) {
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_ = @cmpxchgWeak(usize, &self.state, state, state | MUTEX_LOCK, .Acquire, .Monotonic) orelse return;
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} else if (state & QUEUE_MASK == 0) {
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break;
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}
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SpinLock.yield();
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state = @atomicLoad(usize, &self.state, .Monotonic);
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}
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// create the ResetEvent node on the stack
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// (faster than threadlocal on platforms like OSX)
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var node: Node = undefined;
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node.event = ResetEvent.init();
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defer node.event.deinit();
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// we've spun too long, try and add our node to the LIFO queue.
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// if the mutex becomes available in the process, try and grab it instead.
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while (true) {
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if (state & MUTEX_LOCK == 0) {
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_ = @cmpxchgWeak(usize, &self.state, state, state | MUTEX_LOCK, .Acquire, .Monotonic) orelse return;
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} else {
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node.next = @intToPtr(?*Node, state & QUEUE_MASK);
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const new_state = @ptrToInt(&node) | (state & ~QUEUE_MASK);
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_ = @cmpxchgWeak(usize, &self.state, state, new_state, .Release, .Monotonic) orelse {
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node.event.wait();
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break;
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};
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}
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SpinLock.yield();
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state = @atomicLoad(usize, &self.state, .Monotonic);
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}
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}
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}
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pub const Held = struct {
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mutex: *Mutex,
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pub fn release(self: Held) void {
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// since MUTEX_LOCK is the first bit, we can use (.Sub) instead of (.And, ~MUTEX_LOCK).
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// this is because .Sub may be implemented more efficiently than the latter
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// (e.g. `lock xadd` vs `cmpxchg` loop on x86)
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// first, remove the lock bit so another possibly parallel acquire() can succeed.
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// use .Sub since it can be usually compiled down more efficiency
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// (`lock sub` on x86) vs .And ~MUTEX_LOCK (`lock cmpxchg` loop on x86)
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const state = @atomicRmw(usize, &self.mutex.state, .Sub, MUTEX_LOCK, .Release);
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if ((state & QUEUE_MASK) != 0 and (state & QUEUE_LOCK) == 0) {
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self.mutex.releaseSlow(state);
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}
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// if the LIFO queue isnt locked and it has a node, try and wake up the node.
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if ((state & QUEUE_LOCK) == 0 and (state & QUEUE_MASK) != 0)
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self.mutex.releaseSlow();
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}
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};
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pub fn acquire(self: *Mutex) Held {
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// fast path close to SpinLock fast path
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if (@cmpxchgWeak(usize, &self.state, 0, MUTEX_LOCK, .Acquire, .Monotonic)) |current_state| {
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self.acquireSlow(current_state);
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}
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return Held{ .mutex = self };
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}
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fn acquireSlow(self: *Mutex, current_state: usize) void {
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var spin: usize = 0;
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var state = current_state;
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while (true) {
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// try and acquire the lock if unlocked
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if ((state & MUTEX_LOCK) == 0) {
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state = @cmpxchgWeak(usize, &self.state, state, state | MUTEX_LOCK, .Acquire, .Monotonic) orelse return;
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continue;
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}
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// spin only if the waiting queue isn't empty and when it hasn't spun too much already
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if ((state & QUEUE_MASK) == 0 and spin < SPIN_CPU + SPIN_THREAD) {
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if (spin < SPIN_CPU) {
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std.SpinLock.yield(SPIN_CPU_COUNT);
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} else {
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std.os.sched_yield() catch std.time.sleep(0);
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}
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state = @atomicLoad(usize, &self.state, .Monotonic);
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continue;
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}
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// thread should block, try and add this event to the waiting queue
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var node = QueueNode{
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.next = @intToPtr(?*QueueNode, state & QUEUE_MASK),
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.data = ResetEvent.init(),
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};
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defer node.data.deinit();
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const new_state = @ptrToInt(&node) | (state & ~QUEUE_MASK);
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state = @cmpxchgWeak(usize, &self.state, state, new_state, .Release, .Monotonic) orelse {
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// node is in the queue, wait until a `held.release()` wakes us up.
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_ = node.data.wait(null) catch unreachable;
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spin = 0;
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state = @atomicLoad(usize, &self.state, .Monotonic);
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continue;
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};
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}
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}
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fn releaseSlow(self: *Mutex, current_state: usize) void {
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// grab the QUEUE_LOCK in order to signal a waiting queue node's event.
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var state = current_state;
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while (true) {
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if ((state & QUEUE_LOCK) != 0 or (state & QUEUE_MASK) == 0)
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fn releaseSlow(self: *Mutex) void {
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@setCold(true);
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// try and lock the LFIO queue to pop a node off,
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// stopping altogether if its already locked or the queue is empty
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var state = @atomicLoad(usize, &self.state, .Monotonic);
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while (true) : (SpinLock.loopHint(1)) {
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if (state & QUEUE_LOCK != 0 or state & QUEUE_MASK == 0)
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return;
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state = @cmpxchgWeak(usize, &self.state, state, state | QUEUE_LOCK, .Acquire, .Monotonic) orelse break;
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}
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while (true) {
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// barrier needed to observe incoming state changes
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defer @fence(.Acquire);
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// the mutex is currently locked. try to unset the QUEUE_LOCK and let the locker wake up the next node.
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// avoids waking up multiple sleeping threads which try to acquire the lock again which increases contention.
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// acquired the QUEUE_LOCK, try and pop a node to wake it.
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// if the mutex is locked, then unset QUEUE_LOCK and let
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// the thread who holds the mutex do the wake-up on unlock()
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while (true) : (SpinLock.loopHint(1)) {
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if ((state & MUTEX_LOCK) != 0) {
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state = @cmpxchgWeak(usize, &self.state, state, state & ~QUEUE_LOCK, .Release, .Monotonic) orelse return;
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continue;
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state = @cmpxchgWeak(usize, &self.state, state, state & ~QUEUE_LOCK, .Release, .Acquire) orelse return;
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} else {
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const node = @intToPtr(*Node, state & QUEUE_MASK);
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const new_state = @ptrToInt(node.next);
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state = @cmpxchgWeak(usize, &self.state, state, new_state, .Release, .Acquire) orelse {
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node.event.set();
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return;
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};
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}
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// try to pop the top node on the waiting queue stack to wake it up
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// while at the same time unsetting the QUEUE_LOCK.
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const node = @intToPtr(*QueueNode, state & QUEUE_MASK);
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const new_state = @ptrToInt(node.next) | (state & MUTEX_LOCK);
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state = @cmpxchgWeak(usize, &self.state, state, new_state, .Release, .Monotonic) orelse {
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_ = node.data.set(false);
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return;
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};
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}
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}
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};
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}
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// for platforms without a known OS blocking
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// primitive, default to SpinLock for correctness
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else SpinLock;
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const TestContext = struct {
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mutex: *Mutex,
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@ -1,8 +1,8 @@
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const std = @import("std.zig");
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const builtin = @import("builtin");
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const testing = std.testing;
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const SpinLock = std.SpinLock;
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const assert = std.debug.assert;
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const Backoff = std.SpinLock.Backoff;
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const c = std.c;
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const os = std.os;
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const time = std.time;
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@ -14,13 +14,20 @@ const windows = os.windows;
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pub const ResetEvent = struct {
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os_event: OsEvent,
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pub const OsEvent =
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if (builtin.single_threaded)
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DebugEvent
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else if (builtin.link_libc and builtin.os != .windows and builtin.os != .linux)
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PosixEvent
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else
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AtomicEvent;
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pub fn init() ResetEvent {
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return ResetEvent{ .os_event = OsEvent.init() };
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}
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pub fn deinit(self: *ResetEvent) void {
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self.os_event.deinit();
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self.* = undefined;
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}
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/// Returns whether or not the event is currenetly set
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@ -29,308 +36,116 @@ pub const ResetEvent = struct {
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}
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/// Sets the event if not already set and
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/// wakes up AT LEAST one thread waiting the event.
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/// Returns whether or not a thread was woken up.
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pub fn set(self: *ResetEvent, auto_reset: bool) bool {
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return self.os_event.set(auto_reset);
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/// wakes up at least one thread waiting the event.
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pub fn set(self: *ResetEvent) void {
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return self.os_event.set();
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}
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/// Resets the event to its original, unset state.
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/// Returns whether or not the event was currently set before un-setting.
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pub fn reset(self: *ResetEvent) bool {
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pub fn reset(self: *ResetEvent) void {
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return self.os_event.reset();
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}
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const WaitError = error{
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/// The thread blocked longer than the maximum time specified.
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TimedOut,
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};
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/// Wait for the event to be set by blocking the current thread.
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pub fn wait(self: *ResetEvent) void {
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return self.os_event.wait(null) catch unreachable;
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}
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/// Wait for the event to be set by blocking the current thread.
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/// Optionally provided timeout in nanoseconds which throws an
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/// `error.TimedOut` if the thread blocked AT LEAST longer than specified.
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/// Returns whether or not the thread blocked from the event being unset at the time of calling.
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pub fn wait(self: *ResetEvent, timeout_ns: ?u64) WaitError!bool {
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/// A timeout in nanoseconds can be provided as a hint for how
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/// long the thread should block on the unset event before throwind error.TimedOut.
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pub fn timedWait(self: *ResetEvent, timeout_ns: u64) !void {
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return self.os_event.wait(timeout_ns);
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}
|
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};
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const OsEvent = if (builtin.single_threaded) DebugEvent else switch (builtin.os) {
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.windows => WindowsEvent,
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.linux => if (builtin.link_libc) PosixEvent else LinuxEvent,
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else => if (builtin.link_libc) PosixEvent else SpinEvent,
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};
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const DebugEvent = struct {
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is_set: @TypeOf(set_init),
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is_set: bool,
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const set_init = if (std.debug.runtime_safety) false else {};
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pub fn init() DebugEvent {
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return DebugEvent{ .is_set = set_init };
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fn init() DebugEvent {
|
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return DebugEvent{ .is_set = false };
|
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}
|
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|
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pub fn deinit(self: *DebugEvent) void {
|
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fn deinit(self: *DebugEvent) void {
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self.* = undefined;
|
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}
|
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|
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pub fn isSet(self: *DebugEvent) bool {
|
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if (!std.debug.runtime_safety)
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return true;
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fn isSet(self: *DebugEvent) bool {
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return self.is_set;
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}
|
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pub fn set(self: *DebugEvent, auto_reset: bool) bool {
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if (std.debug.runtime_safety)
|
||||
self.is_set = !auto_reset;
|
||||
return false;
|
||||
}
|
||||
|
||||
pub fn reset(self: *DebugEvent) bool {
|
||||
if (!std.debug.runtime_safety)
|
||||
return false;
|
||||
const was_set = self.is_set;
|
||||
fn reset(self: *DebugEvent) void {
|
||||
self.is_set = false;
|
||||
return was_set;
|
||||
}
|
||||
|
||||
pub fn wait(self: *DebugEvent, timeout: ?u64) ResetEvent.WaitError!bool {
|
||||
if (std.debug.runtime_safety and !self.is_set)
|
||||
@panic("deadlock detected");
|
||||
return ResetEvent.WaitError.TimedOut;
|
||||
fn set(self: *DebugEvent) void {
|
||||
self.is_set = true;
|
||||
}
|
||||
|
||||
fn wait(self: *DebugEvent, timeout: ?u64) !void {
|
||||
if (self.is_set)
|
||||
return;
|
||||
if (timeout != null)
|
||||
return error.TimedOut;
|
||||
@panic("deadlock detected");
|
||||
}
|
||||
};
|
||||
|
||||
fn AtomicEvent(comptime FutexImpl: type) type {
|
||||
return struct {
|
||||
state: u32,
|
||||
|
||||
const IS_SET: u32 = 1 << 0;
|
||||
const WAIT_MASK = ~IS_SET;
|
||||
|
||||
pub const Self = @This();
|
||||
pub const Futex = FutexImpl;
|
||||
|
||||
pub fn init() Self {
|
||||
return Self{ .state = 0 };
|
||||
}
|
||||
|
||||
pub fn deinit(self: *Self) void {
|
||||
self.* = undefined;
|
||||
}
|
||||
|
||||
pub fn isSet(self: *const Self) bool {
|
||||
const state = @atomicLoad(u32, &self.state, .Acquire);
|
||||
return (state & IS_SET) != 0;
|
||||
}
|
||||
|
||||
pub fn reset(self: *Self) bool {
|
||||
const old_state = @atomicRmw(u32, &self.state, .Xchg, 0, .Monotonic);
|
||||
return (old_state & IS_SET) != 0;
|
||||
}
|
||||
|
||||
pub fn set(self: *Self, auto_reset: bool) bool {
|
||||
const new_state = if (auto_reset) 0 else IS_SET;
|
||||
const old_state = @atomicRmw(u32, &self.state, .Xchg, new_state, .Release);
|
||||
if ((old_state & WAIT_MASK) == 0) {
|
||||
return false;
|
||||
}
|
||||
|
||||
Futex.wake(&self.state);
|
||||
return true;
|
||||
}
|
||||
|
||||
pub fn wait(self: *Self, timeout: ?u64) ResetEvent.WaitError!bool {
|
||||
var dummy_value: u32 = undefined;
|
||||
const wait_token = @truncate(u32, @ptrToInt(&dummy_value));
|
||||
|
||||
var state = @atomicLoad(u32, &self.state, .Monotonic);
|
||||
while (true) {
|
||||
if ((state & IS_SET) != 0)
|
||||
return false;
|
||||
state = @cmpxchgWeak(u32, &self.state, state, wait_token, .Acquire, .Monotonic) orelse break;
|
||||
}
|
||||
|
||||
try Futex.wait(&self.state, wait_token, timeout);
|
||||
return true;
|
||||
}
|
||||
};
|
||||
}
|
||||
|
||||
const SpinEvent = AtomicEvent(struct {
|
||||
fn wake(ptr: *const u32) void {}
|
||||
|
||||
fn wait(ptr: *const u32, expected: u32, timeout: ?u64) ResetEvent.WaitError!void {
|
||||
// TODO: handle platforms where time.Timer.start() fails
|
||||
var spin = Backoff.init();
|
||||
var timer = if (timeout == null) null else time.Timer.start() catch unreachable;
|
||||
while (@atomicLoad(u32, ptr, .Acquire) == expected) {
|
||||
spin.yield();
|
||||
if (timeout) |timeout_ns| {
|
||||
if (timer.?.read() > timeout_ns)
|
||||
return ResetEvent.WaitError.TimedOut;
|
||||
}
|
||||
}
|
||||
}
|
||||
});
|
||||
|
||||
const LinuxEvent = AtomicEvent(struct {
|
||||
fn wake(ptr: *const u32) void {
|
||||
const key = @ptrCast(*const i32, ptr);
|
||||
const rc = linux.futex_wake(key, linux.FUTEX_WAKE | linux.FUTEX_PRIVATE_FLAG, 1);
|
||||
assert(linux.getErrno(rc) == 0);
|
||||
}
|
||||
|
||||
fn wait(ptr: *const u32, expected: u32, timeout: ?u64) ResetEvent.WaitError!void {
|
||||
var ts: linux.timespec = undefined;
|
||||
var ts_ptr: ?*linux.timespec = null;
|
||||
if (timeout) |timeout_ns| {
|
||||
ts_ptr = &ts;
|
||||
ts.tv_sec = @intCast(isize, timeout_ns / time.ns_per_s);
|
||||
ts.tv_nsec = @intCast(isize, timeout_ns % time.ns_per_s);
|
||||
}
|
||||
|
||||
const key = @ptrCast(*const i32, ptr);
|
||||
const key_expect = @bitCast(i32, expected);
|
||||
while (@atomicLoad(i32, key, .Acquire) == key_expect) {
|
||||
const rc = linux.futex_wait(key, linux.FUTEX_WAIT | linux.FUTEX_PRIVATE_FLAG, key_expect, ts_ptr);
|
||||
switch (linux.getErrno(rc)) {
|
||||
0, linux.EAGAIN => break,
|
||||
linux.EINTR => continue,
|
||||
linux.ETIMEDOUT => return ResetEvent.WaitError.TimedOut,
|
||||
else => unreachable,
|
||||
}
|
||||
}
|
||||
}
|
||||
});
|
||||
|
||||
const WindowsEvent = AtomicEvent(struct {
|
||||
fn wake(ptr: *const u32) void {
|
||||
if (getEventHandle()) |handle| {
|
||||
const key = @ptrCast(*const c_void, ptr);
|
||||
const rc = windows.ntdll.NtReleaseKeyedEvent(handle, key, windows.FALSE, null);
|
||||
assert(rc == 0);
|
||||
}
|
||||
}
|
||||
|
||||
fn wait(ptr: *const u32, expected: u32, timeout: ?u64) ResetEvent.WaitError!void {
|
||||
// fallback to spinlock if NT Keyed Events arent available
|
||||
const handle = getEventHandle() orelse {
|
||||
return SpinEvent.Futex.wait(ptr, expected, timeout);
|
||||
};
|
||||
|
||||
// NT uses timeouts in units of 100ns with negative value being relative
|
||||
var timeout_ptr: ?*windows.LARGE_INTEGER = null;
|
||||
var timeout_value: windows.LARGE_INTEGER = undefined;
|
||||
if (timeout) |timeout_ns| {
|
||||
timeout_ptr = &timeout_value;
|
||||
timeout_value = -@intCast(windows.LARGE_INTEGER, timeout_ns / 100);
|
||||
}
|
||||
|
||||
// NtWaitForKeyedEvent doesnt have spurious wake-ups
|
||||
if (@atomicLoad(u32, ptr, .Acquire) == expected) {
|
||||
const key = @ptrCast(*const c_void, ptr);
|
||||
const rc = windows.ntdll.NtWaitForKeyedEvent(handle, key, windows.FALSE, timeout_ptr);
|
||||
switch (rc) {
|
||||
0 => {},
|
||||
windows.WAIT_TIMEOUT => return ResetEvent.WaitError.TimedOut,
|
||||
else => unreachable,
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
var keyed_state = State.Uninitialized;
|
||||
var keyed_handle: ?windows.HANDLE = null;
|
||||
|
||||
const State = enum(u8) {
|
||||
Uninitialized,
|
||||
Intializing,
|
||||
Initialized,
|
||||
};
|
||||
|
||||
fn getEventHandle() ?windows.HANDLE {
|
||||
var spin = Backoff.init();
|
||||
var state = @atomicLoad(State, &keyed_state, .Monotonic);
|
||||
|
||||
while (true) {
|
||||
switch (state) {
|
||||
.Initialized => {
|
||||
return keyed_handle;
|
||||
},
|
||||
.Intializing => {
|
||||
spin.yield();
|
||||
state = @atomicLoad(State, &keyed_state, .Acquire);
|
||||
},
|
||||
.Uninitialized => state = @cmpxchgWeak(State, &keyed_state, state, .Intializing, .Acquire, .Monotonic) orelse {
|
||||
var handle: windows.HANDLE = undefined;
|
||||
const access_mask = windows.GENERIC_READ | windows.GENERIC_WRITE;
|
||||
if (windows.ntdll.NtCreateKeyedEvent(&handle, access_mask, null, 0) == 0)
|
||||
keyed_handle = handle;
|
||||
@atomicStore(State, &keyed_state, .Initialized, .Release);
|
||||
return keyed_handle;
|
||||
},
|
||||
}
|
||||
}
|
||||
}
|
||||
});
|
||||
|
||||
const PosixEvent = struct {
|
||||
state: u32,
|
||||
is_set: bool,
|
||||
cond: c.pthread_cond_t,
|
||||
mutex: c.pthread_mutex_t,
|
||||
|
||||
const IS_SET: u32 = 1;
|
||||
|
||||
pub fn init() PosixEvent {
|
||||
fn init() PosixEvent {
|
||||
return PosixEvent{
|
||||
.state = 0,
|
||||
.is_set = false,
|
||||
.cond = c.PTHREAD_COND_INITIALIZER,
|
||||
.mutex = c.PTHREAD_MUTEX_INITIALIZER,
|
||||
};
|
||||
}
|
||||
|
||||
pub fn deinit(self: *PosixEvent) void {
|
||||
// On dragonfly, the destroy functions return EINVAL if they were initialized statically.
|
||||
fn deinit(self: *PosixEvent) void {
|
||||
// on dragonfly, *destroy() functions can return EINVAL
|
||||
// for statically initialized pthread structures
|
||||
const err = if (builtin.os == .dragonfly) os.EINVAL else 0;
|
||||
|
||||
const retm = c.pthread_mutex_destroy(&self.mutex);
|
||||
assert(retm == 0 or retm == (if (builtin.os == .dragonfly) os.EINVAL else 0));
|
||||
assert(retm == 0 or retm == err);
|
||||
const retc = c.pthread_cond_destroy(&self.cond);
|
||||
assert(retc == 0 or retc == (if (builtin.os == .dragonfly) os.EINVAL else 0));
|
||||
assert(retc == 0 or retc == err);
|
||||
}
|
||||
|
||||
pub fn isSet(self: *PosixEvent) bool {
|
||||
fn isSet(self: *PosixEvent) bool {
|
||||
assert(c.pthread_mutex_lock(&self.mutex) == 0);
|
||||
defer assert(c.pthread_mutex_unlock(&self.mutex) == 0);
|
||||
|
||||
return self.state == IS_SET;
|
||||
return self.is_set;
|
||||
}
|
||||
|
||||
pub fn reset(self: *PosixEvent) bool {
|
||||
fn reset(self: *PosixEvent) void {
|
||||
assert(c.pthread_mutex_lock(&self.mutex) == 0);
|
||||
defer assert(c.pthread_mutex_unlock(&self.mutex) == 0);
|
||||
|
||||
const was_set = self.state == IS_SET;
|
||||
self.state = 0;
|
||||
return was_set;
|
||||
self.is_set = false;
|
||||
}
|
||||
|
||||
pub fn set(self: *PosixEvent, auto_reset: bool) bool {
|
||||
fn set(self: *PosixEvent) void {
|
||||
assert(c.pthread_mutex_lock(&self.mutex) == 0);
|
||||
defer assert(c.pthread_mutex_unlock(&self.mutex) == 0);
|
||||
|
||||
const had_waiter = self.state > IS_SET;
|
||||
self.state = if (auto_reset) 0 else IS_SET;
|
||||
if (had_waiter) {
|
||||
if (!self.is_set) {
|
||||
self.is_set = true;
|
||||
assert(c.pthread_cond_signal(&self.cond) == 0);
|
||||
}
|
||||
return had_waiter;
|
||||
}
|
||||
|
||||
pub fn wait(self: *PosixEvent, timeout: ?u64) ResetEvent.WaitError!bool {
|
||||
fn wait(self: *PosixEvent, timeout: ?u64) !void {
|
||||
assert(c.pthread_mutex_lock(&self.mutex) == 0);
|
||||
defer assert(c.pthread_mutex_unlock(&self.mutex) == 0);
|
||||
|
||||
if (self.state == IS_SET)
|
||||
return false;
|
||||
// quick guard before possibly calling time syscalls below
|
||||
if (self.is_set)
|
||||
return;
|
||||
|
||||
var ts: os.timespec = undefined;
|
||||
if (timeout) |timeout_ns| {
|
||||
@ -349,85 +164,248 @@ const PosixEvent = struct {
|
||||
ts.tv_nsec = @intCast(@TypeOf(ts.tv_nsec), @mod(timeout_abs, time.second));
|
||||
}
|
||||
|
||||
var dummy_value: u32 = undefined;
|
||||
var wait_token = @truncate(u32, @ptrToInt(&dummy_value));
|
||||
self.state = wait_token;
|
||||
|
||||
while (self.state == wait_token) {
|
||||
while (!self.is_set) {
|
||||
const rc = switch (timeout == null) {
|
||||
true => c.pthread_cond_wait(&self.cond, &self.mutex),
|
||||
else => c.pthread_cond_timedwait(&self.cond, &self.mutex, &ts),
|
||||
};
|
||||
// TODO: rc appears to be the positive error code making os.errno() always return 0 on linux
|
||||
switch (std.math.max(@as(c_int, os.errno(rc)), rc)) {
|
||||
switch (rc) {
|
||||
0 => {},
|
||||
os.ETIMEDOUT => return ResetEvent.WaitError.TimedOut,
|
||||
os.ETIMEDOUT => return error.TimedOut,
|
||||
os.EINVAL => unreachable,
|
||||
os.EPERM => unreachable,
|
||||
else => unreachable,
|
||||
}
|
||||
}
|
||||
return true;
|
||||
}
|
||||
};
|
||||
|
||||
test "std.ResetEvent" {
|
||||
// TODO
|
||||
if (builtin.single_threaded)
|
||||
return error.SkipZigTest;
|
||||
const AtomicEvent = struct {
|
||||
state: State,
|
||||
|
||||
const State = enum(i32) {
|
||||
Empty,
|
||||
Waiting,
|
||||
Signaled,
|
||||
};
|
||||
|
||||
fn init() AtomicEvent {
|
||||
return AtomicEvent{ .state = .Empty };
|
||||
}
|
||||
|
||||
fn deinit(self: *AtomicEvent) void {
|
||||
self.* = undefined;
|
||||
}
|
||||
|
||||
fn isSet(self: *AtomicEvent) bool {
|
||||
return @atomicLoad(State, &self.state, .Acquire) == .Signaled;
|
||||
}
|
||||
|
||||
fn reset(self: *AtomicEvent) void {
|
||||
@atomicStore(State, &self.state, .Empty, .Monotonic);
|
||||
}
|
||||
|
||||
fn set(self: *AtomicEvent) void {
|
||||
if (@atomicRmw(State, &self.state, .Xchg, .Signaled, .Release) == .Waiting)
|
||||
Futex.wake(@ptrCast(*i32, &self.state));
|
||||
}
|
||||
|
||||
fn wait(self: *AtomicEvent, timeout: ?u64) !void {
|
||||
var state = @atomicLoad(State, &self.state, .Monotonic);
|
||||
while (state == .Empty) {
|
||||
state = @cmpxchgWeak(State, &self.state, .Empty, .Waiting, .Acquire, .Monotonic) orelse
|
||||
return Futex.wait(@ptrCast(*i32, &self.state), @enumToInt(State.Waiting), timeout);
|
||||
}
|
||||
}
|
||||
|
||||
pub const Futex = switch (builtin.os) {
|
||||
.windows => WindowsFutex,
|
||||
.linux => LinuxFutex,
|
||||
else => SpinFutex,
|
||||
};
|
||||
|
||||
const SpinFutex = struct {
|
||||
fn wake(ptr: *i32) void {}
|
||||
|
||||
fn wait(ptr: *i32, expected: i32, timeout: ?u64) !void {
|
||||
// TODO: handle platforms where a monotonic timer isnt available
|
||||
var timer: time.Timer = undefined;
|
||||
if (timeout != null)
|
||||
timer = time.Timer.start() catch unreachable;
|
||||
|
||||
while (@atomicLoad(i32, ptr, .Acquire) == expected) {
|
||||
SpinLock.yield();
|
||||
if (timeout) |timeout_ns| {
|
||||
if (timer.read() >= timeout_ns)
|
||||
return error.TimedOut;
|
||||
}
|
||||
}
|
||||
}
|
||||
};
|
||||
|
||||
const LinuxFutex = struct {
|
||||
fn wake(ptr: *i32) void {
|
||||
const rc = linux.futex_wake(ptr, linux.FUTEX_WAKE | linux.FUTEX_PRIVATE_FLAG, 1);
|
||||
assert(linux.getErrno(rc) == 0);
|
||||
}
|
||||
|
||||
fn wait(ptr: *i32, expected: i32, timeout: ?u64) !void {
|
||||
var ts: linux.timespec = undefined;
|
||||
var ts_ptr: ?*linux.timespec = null;
|
||||
if (timeout) |timeout_ns| {
|
||||
ts_ptr = &ts;
|
||||
ts.tv_sec = @intCast(isize, timeout_ns / time.ns_per_s);
|
||||
ts.tv_nsec = @intCast(isize, timeout_ns % time.ns_per_s);
|
||||
}
|
||||
|
||||
while (@atomicLoad(i32, ptr, .Acquire) == expected) {
|
||||
const rc = linux.futex_wait(ptr, linux.FUTEX_WAIT | linux.FUTEX_PRIVATE_FLAG, expected, ts_ptr);
|
||||
switch (linux.getErrno(rc)) {
|
||||
0 => continue,
|
||||
os.ETIMEDOUT => return error.TimedOut,
|
||||
os.EINTR => continue,
|
||||
os.EAGAIN => return,
|
||||
else => unreachable,
|
||||
}
|
||||
}
|
||||
}
|
||||
};
|
||||
|
||||
const WindowsFutex = struct {
|
||||
pub fn wake(ptr: *i32) void {
|
||||
const handle = getEventHandle() orelse return SpinFutex.wake(ptr);
|
||||
const key = @ptrCast(*const c_void, ptr);
|
||||
const rc = windows.ntdll.NtReleaseKeyedEvent(handle, key, windows.FALSE, null);
|
||||
assert(rc == 0);
|
||||
}
|
||||
|
||||
pub fn wait(ptr: *i32, expected: i32, timeout: ?u64) !void {
|
||||
const handle = getEventHandle() orelse return SpinFutex.wait(ptr, expected, timeout);
|
||||
|
||||
// NT uses timeouts in units of 100ns with negative value being relative
|
||||
var timeout_ptr: ?*windows.LARGE_INTEGER = null;
|
||||
var timeout_value: windows.LARGE_INTEGER = undefined;
|
||||
if (timeout) |timeout_ns| {
|
||||
timeout_ptr = &timeout_value;
|
||||
timeout_value = -@intCast(windows.LARGE_INTEGER, timeout_ns / 100);
|
||||
}
|
||||
|
||||
// NtWaitForKeyedEvent doesnt have spurious wake-ups
|
||||
const key = @ptrCast(*const c_void, ptr);
|
||||
const rc = windows.ntdll.NtWaitForKeyedEvent(handle, key, windows.FALSE, timeout_ptr);
|
||||
switch (rc) {
|
||||
windows.WAIT_TIMEOUT => return error.TimedOut,
|
||||
windows.WAIT_OBJECT_0 => {},
|
||||
else => unreachable,
|
||||
}
|
||||
}
|
||||
|
||||
var event_handle: usize = EMPTY;
|
||||
const EMPTY = ~@as(usize, 0);
|
||||
const LOADING = EMPTY - 1;
|
||||
|
||||
pub fn getEventHandle() ?windows.HANDLE {
|
||||
var handle = @atomicLoad(usize, &event_handle, .Monotonic);
|
||||
while (true) {
|
||||
switch (handle) {
|
||||
EMPTY => handle = @cmpxchgWeak(usize, &event_handle, EMPTY, LOADING, .Acquire, .Monotonic) orelse {
|
||||
const handle_ptr = @ptrCast(*windows.HANDLE, &handle);
|
||||
const access_mask = windows.GENERIC_READ | windows.GENERIC_WRITE;
|
||||
if (windows.ntdll.NtCreateKeyedEvent(handle_ptr, access_mask, null, 0) != 0)
|
||||
handle = 0;
|
||||
@atomicStore(usize, &event_handle, handle, .Monotonic);
|
||||
return @intToPtr(?windows.HANDLE, handle);
|
||||
},
|
||||
LOADING => {
|
||||
SpinLock.yield();
|
||||
handle = @atomicLoad(usize, &event_handle, .Monotonic);
|
||||
},
|
||||
else => {
|
||||
return @intToPtr(?windows.HANDLE, handle);
|
||||
},
|
||||
}
|
||||
}
|
||||
}
|
||||
};
|
||||
};
|
||||
|
||||
test "std.ResetEvent" {
|
||||
var event = ResetEvent.init();
|
||||
defer event.deinit();
|
||||
|
||||
// test event setting
|
||||
testing.expect(event.isSet() == false);
|
||||
testing.expect(event.set(false) == false);
|
||||
event.set();
|
||||
testing.expect(event.isSet() == true);
|
||||
|
||||
// test event resetting
|
||||
testing.expect(event.reset() == true);
|
||||
event.reset();
|
||||
testing.expect(event.isSet() == false);
|
||||
testing.expect(event.reset() == false);
|
||||
|
||||
// test cross thread signaling
|
||||
// test event waiting (non-blocking)
|
||||
event.set();
|
||||
event.wait();
|
||||
try event.timedWait(1);
|
||||
|
||||
// test cross-thread signaling
|
||||
if (builtin.single_threaded)
|
||||
return;
|
||||
|
||||
const Context = struct {
|
||||
event: ResetEvent,
|
||||
const Self = @This();
|
||||
|
||||
value: u128,
|
||||
in: ResetEvent,
|
||||
out: ResetEvent,
|
||||
|
||||
fn receiver(self: *@This()) void {
|
||||
// wait for the sender to notify us with updated value
|
||||
assert(self.value == 0);
|
||||
assert((self.event.wait(1 * time.second) catch unreachable) == true);
|
||||
assert(self.value == 1);
|
||||
|
||||
// wait for sender to sleep, then notify it of new value
|
||||
time.sleep(50 * time.millisecond);
|
||||
self.value = 2;
|
||||
assert(self.event.set(false) == true);
|
||||
fn init() Self {
|
||||
return Self{
|
||||
.value = 0,
|
||||
.in = ResetEvent.init(),
|
||||
.out = ResetEvent.init(),
|
||||
};
|
||||
}
|
||||
|
||||
fn sender(self: *@This()) !void {
|
||||
// wait for the receiver() to start wait()'ing
|
||||
time.sleep(50 * time.millisecond);
|
||||
fn deinit(self: *Self) void {
|
||||
self.in.deinit();
|
||||
self.out.deinit();
|
||||
self.* = undefined;
|
||||
}
|
||||
|
||||
// update value to 1 and notify the receiver()
|
||||
assert(self.value == 0);
|
||||
fn sender(self: *Self) void {
|
||||
// update value and signal input
|
||||
testing.expect(self.value == 0);
|
||||
self.value = 1;
|
||||
assert(self.event.set(true) == true);
|
||||
self.in.set();
|
||||
|
||||
// wait for the receiver to update the value & notify us
|
||||
assert((try self.event.wait(1 * time.second)) == true);
|
||||
assert(self.value == 2);
|
||||
// wait for receiver to update value and signal output
|
||||
self.out.wait();
|
||||
testing.expect(self.value == 2);
|
||||
|
||||
// update value and signal final input
|
||||
self.value = 3;
|
||||
self.in.set();
|
||||
}
|
||||
|
||||
fn receiver(self: *Self) void {
|
||||
// wait for sender to update value and signal input
|
||||
self.in.wait();
|
||||
assert(self.value == 1);
|
||||
|
||||
// update value and signal output
|
||||
self.in.reset();
|
||||
self.value = 2;
|
||||
self.out.set();
|
||||
|
||||
// wait for sender to update value and signal final input
|
||||
self.in.wait();
|
||||
assert(self.value == 3);
|
||||
}
|
||||
};
|
||||
|
||||
_ = event.reset();
|
||||
var context = Context{
|
||||
.event = event,
|
||||
.value = 0,
|
||||
};
|
||||
|
||||
var receiver = try std.Thread.spawn(&context, Context.receiver);
|
||||
var context = Context.init();
|
||||
defer context.deinit();
|
||||
const receiver = try std.Thread.spawn(&context, Context.receiver);
|
||||
defer receiver.wait();
|
||||
try context.sender();
|
||||
context.sender();
|
||||
}
|
||||
|
||||
@ -1,69 +1,77 @@
|
||||
const std = @import("std.zig");
|
||||
const builtin = @import("builtin");
|
||||
const assert = std.debug.assert;
|
||||
const time = std.time;
|
||||
const os = std.os;
|
||||
|
||||
pub const SpinLock = struct {
|
||||
lock: u8, // TODO use a bool or enum
|
||||
state: State,
|
||||
|
||||
const State = enum(u8) {
|
||||
Unlocked,
|
||||
Locked,
|
||||
};
|
||||
|
||||
pub const Held = struct {
|
||||
spinlock: *SpinLock,
|
||||
|
||||
pub fn release(self: Held) void {
|
||||
@atomicStore(u8, &self.spinlock.lock, 0, .Release);
|
||||
@atomicStore(State, &self.spinlock.state, .Unlocked, .Release);
|
||||
}
|
||||
};
|
||||
|
||||
pub fn init() SpinLock {
|
||||
return SpinLock{ .lock = 0 };
|
||||
return SpinLock{ .state = .Unlocked };
|
||||
}
|
||||
|
||||
pub fn deinit(self: *SpinLock) void {
|
||||
self.* = undefined;
|
||||
}
|
||||
|
||||
pub fn tryAcquire(self: *SpinLock) ?Held {
|
||||
return switch (@atomicRmw(State, &self.state, .Xchg, .Locked, .Acquire)) {
|
||||
.Unlocked => Held{ .spinlock = self },
|
||||
.Locked => null,
|
||||
};
|
||||
}
|
||||
|
||||
pub fn acquire(self: *SpinLock) Held {
|
||||
var backoff = Backoff.init();
|
||||
while (@atomicRmw(u8, &self.lock, .Xchg, 1, .Acquire) != 0)
|
||||
backoff.yield();
|
||||
return Held{ .spinlock = self };
|
||||
while (true) {
|
||||
return self.tryAcquire() orelse {
|
||||
yield();
|
||||
continue;
|
||||
};
|
||||
}
|
||||
}
|
||||
|
||||
pub fn yield(iterations: usize) void {
|
||||
pub fn yield() void {
|
||||
// On native windows, SwitchToThread is too expensive,
|
||||
// and yielding for 380-410 iterations was found to be
|
||||
// a nice sweet spot. Posix systems on the other hand,
|
||||
// especially linux, perform better by yielding the thread.
|
||||
switch (builtin.os) {
|
||||
.windows => loopHint(400),
|
||||
else => std.os.sched_yield() catch loopHint(1),
|
||||
}
|
||||
}
|
||||
|
||||
/// Hint to the cpu that execution is spinning
|
||||
/// for the given amount of iterations.
|
||||
pub fn loopHint(iterations: usize) void {
|
||||
var i = iterations;
|
||||
while (i != 0) : (i -= 1) {
|
||||
switch (builtin.arch) {
|
||||
.i386, .x86_64 => asm volatile ("pause"),
|
||||
.arm, .aarch64 => asm volatile ("yield"),
|
||||
else => time.sleep(0),
|
||||
// these instructions use a memory clobber as they
|
||||
// flush the pipeline of any speculated reads/writes.
|
||||
.i386, .x86_64 => asm volatile ("pause" ::: "memory"),
|
||||
.arm, .aarch64 => asm volatile ("yield" ::: "memory"),
|
||||
else => std.os.sched_yield() catch {},
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/// Provides a method to incrementally yield longer each time its called.
|
||||
pub const Backoff = struct {
|
||||
iteration: usize,
|
||||
|
||||
pub fn init() @This() {
|
||||
return @This(){ .iteration = 0 };
|
||||
}
|
||||
|
||||
/// Modified hybrid yielding from
|
||||
/// http://www.1024cores.net/home/lock-free-algorithms/tricks/spinning
|
||||
pub fn yield(self: *@This()) void {
|
||||
defer self.iteration +%= 1;
|
||||
if (self.iteration < 20) {
|
||||
SpinLock.yield(self.iteration);
|
||||
} else if (self.iteration < 24) {
|
||||
os.sched_yield() catch time.sleep(1);
|
||||
} else if (self.iteration < 26) {
|
||||
time.sleep(1 * time.millisecond);
|
||||
} else {
|
||||
time.sleep(10 * time.millisecond);
|
||||
}
|
||||
}
|
||||
};
|
||||
};
|
||||
|
||||
test "spinlock" {
|
||||
var lock = SpinLock.init();
|
||||
defer lock.deinit();
|
||||
|
||||
const held = lock.acquire();
|
||||
defer held.release();
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user