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// SPDX-License-Identifier: MIT
// Copyright (c) 2015-2021 Zig Contributors
// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
// The MIT license requires this copyright notice to be included in all copies
// and substantial portions of the software.
//! A condition provides a way for a kernel thread to block until it is signaled
//! to wake up. Spurious wakeups are possible.
//! This API supports static initialization and does not require deinitialization.
impl: Impl,
const std = @import("../std.zig");
const Condition = @This();
const windows = std.os.windows;
const linux = std.os.linux;
const Mutex = std.Thread.Mutex;
const assert = std.debug.assert;
const Impl = if (std.builtin.single_threaded)
SingleThreadedCondition
else if (std.Target.current.os.tag == .windows)
WindowsCondition
else if (std.Thread.use_pthreads)
PthreadCondition
else
AtomicCondition;
pub const SingleThreadedCondition = struct {
pub fn wait(cond: *SingleThreadedCondition, mutex: *Mutex) void {
unreachable; // deadlock detected
}
pub fn signal(cond: *SingleThreadedCondition) void {}
pub fn broadcast(cond: *SingleThreadedCondition) void {}
};
pub const WindowsCondition = struct {
cond: windows.CONDITION_VARIABLE = windows.CONDITION_VARIABLE_INIT,
pub fn wait(cond: *WindowsCondition, mutex: *Mutex) void {
const rc = windows.kernel32.SleepConditionVariableSRW(
&cond.cond,
&mutex.srwlock,
windows.INFINITE,
@as(windows.ULONG, 0),
);
assert(rc != windows.FALSE);
}
pub fn signal(cond: *WindowsCondition) void {
windows.kernel32.WakeConditionVariable(&cond.cond);
}
pub fn broadcast(cond: *WindowsCondition) void {
windows.kernel32.WakeAllConditionVariable(&cond.cond);
}
};
pub const PthreadCondition = struct {
cond: std.c.pthread_cond_t = .{},
pub fn wait(cond: *PthreadCondition, mutex: *Mutex) void {
const rc = std.c.pthread_cond_wait(&cond.cond, &mutex.mutex);
assert(rc == 0);
}
pub fn signal(cond: *PthreadCondition) void {
const rc = std.c.pthread_cond_signal(&cond.cond);
assert(rc == 0);
}
pub fn broadcast(cond: *PthreadCondition) void {
const rc = std.c.pthread_cond_broadcast(&cond.cond);
assert(rc == 0);
}
};
pub const AtomicCondition = struct {
pending: bool = false,
queue_mutex: Mutex = .{},
queue_list: QueueList = .{},
pub const QueueList = std.SinglyLinkedList(QueueItem);
pub const QueueItem = struct {
futex: i32 = 0,
fn wait(cond: *@This()) void {
while (@atomicLoad(i32, &cond.futex, .Acquire) == 0) {
switch (std.Target.current.os.tag) {
.linux => {
switch (linux.getErrno(linux.futex_wait(
&cond.futex,
linux.FUTEX_PRIVATE_FLAG | linux.FUTEX_WAIT,
0,
null,
))) {
0 => {},
std.os.EINTR => {},
std.os.EAGAIN => {},
else => unreachable,
}
},
else => spinLoopHint(),
}
}
}
fn notify(cond: *@This()) void {
@atomicStore(i32, &cond.futex, 1, .Release);
switch (std.Target.current.os.tag) {
.linux => {
switch (linux.getErrno(linux.futex_wake(
&cond.futex,
linux.FUTEX_PRIVATE_FLAG | linux.FUTEX_WAKE,
1,
))) {
0 => {},
std.os.EFAULT => {},
else => unreachable,
}
},
else => {},
}
}
};
pub fn wait(cond: *AtomicCondition, mutex: *Mutex) void {
var waiter = QueueList.Node{ .data = .{} };
{
const held = cond.queue_mutex.acquire();
defer held.release();
cond.queue_list.prepend(&waiter);
@atomicStore(bool, &cond.pending, true, .SeqCst);
}
mutex.unlock();
waiter.data.wait();
mutex.lock();
}
pub fn signal(cond: *AtomicCondition) void {
if (@atomicLoad(bool, &cond.pending, .SeqCst) == false)
return;
const maybe_waiter = blk: {
const held = cond.queue_mutex.acquire();
defer held.release();
const maybe_waiter = cond.queue_list.popFirst();
@atomicStore(bool, &cond.pending, cond.queue_list.first != null, .SeqCst);
break :blk maybe_waiter;
};
if (maybe_waiter) |waiter|
waiter.data.notify();
}
pub fn broadcast(cond: *AtomicCondition) void {
if (@atomicLoad(bool, &cond.pending, .SeqCst) == false)
return;
@atomicStore(bool, &cond.pending, false, .SeqCst);
var waiters = blk: {
const held = cond.queue_mutex.acquire();
defer held.release();
const waiters = cond.queue_list;
cond.queue_list = .{};
break :blk waiters;
};
while (waiters.popFirst()) |waiter|
waiter.data.notify();
}
};
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