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|
//! 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 builtin = @import("builtin");
const Condition = @This();
const windows = std.os.windows;
const linux = std.os.linux;
const Mutex = std.Thread.Mutex;
const assert = std.debug.assert;
const testing = std.testing;
pub fn wait(cond: *Condition, mutex: *Mutex) void {
cond.impl.wait(mutex);
}
pub fn signal(cond: *Condition) void {
cond.impl.signal();
}
pub fn broadcast(cond: *Condition) void {
cond.impl.broadcast();
}
const Impl = if (builtin.single_threaded)
SingleThreadedCondition
else if (builtin.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 {
_ = cond;
_ = mutex;
unreachable; // deadlock detected
}
pub fn signal(cond: *SingleThreadedCondition) void {
_ = cond;
}
pub fn broadcast(cond: *SingleThreadedCondition) void {
_ = cond;
}
};
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.impl.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.impl.pthread_mutex);
assert(rc == .SUCCESS);
}
pub fn signal(cond: *PthreadCondition) void {
const rc = std.c.pthread_cond_signal(&cond.cond);
assert(rc == .SUCCESS);
}
pub fn broadcast(cond: *PthreadCondition) void {
const rc = std.c.pthread_cond_broadcast(&cond.cond);
assert(rc == .SUCCESS);
}
};
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 (builtin.os.tag) {
.linux => {
switch (linux.getErrno(linux.futex_wait(
&cond.futex,
linux.FUTEX.PRIVATE_FLAG | linux.FUTEX.WAIT,
0,
null,
))) {
.SUCCESS => {},
.INTR => {},
.AGAIN => {},
else => unreachable,
}
},
else => std.atomic.spinLoopHint(),
}
}
}
fn notify(cond: *@This()) void {
@atomicStore(i32, &cond.futex, 1, .Release);
switch (builtin.os.tag) {
.linux => {
switch (linux.getErrno(linux.futex_wake(
&cond.futex,
linux.FUTEX.PRIVATE_FLAG | linux.FUTEX.WAKE,
1,
))) {
.SUCCESS => {},
.FAULT => {},
else => unreachable,
}
},
else => {},
}
}
};
pub fn wait(cond: *AtomicCondition, mutex: *Mutex) void {
var waiter = QueueList.Node{ .data = .{} };
{
cond.queue_mutex.lock();
defer cond.queue_mutex.unlock();
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: {
cond.queue_mutex.lock();
defer cond.queue_mutex.unlock();
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: {
cond.queue_mutex.lock();
defer cond.queue_mutex.unlock();
const waiters = cond.queue_list;
cond.queue_list = .{};
break :blk waiters;
};
while (waiters.popFirst()) |waiter|
waiter.data.notify();
}
};
test "Thread.Condition" {
if (builtin.single_threaded) {
return error.SkipZigTest;
}
const TestContext = struct {
cond: *Condition,
cond_main: *Condition,
mutex: *Mutex,
n: *i32,
fn worker(ctx: *@This()) void {
ctx.mutex.lock();
ctx.n.* += 1;
ctx.cond_main.signal();
ctx.cond.wait(ctx.mutex);
ctx.n.* -= 1;
ctx.cond_main.signal();
ctx.mutex.unlock();
}
};
const num_threads = 3;
var threads: [num_threads]std.Thread = undefined;
var cond = Condition{};
var cond_main = Condition{};
var mut = Mutex{};
var n: i32 = 0;
var ctx = TestContext{ .cond = &cond, .cond_main = &cond_main, .mutex = &mut, .n = &n };
mut.lock();
for (threads) |*t| t.* = try std.Thread.spawn(.{}, TestContext.worker, .{&ctx});
cond_main.wait(&mut);
while (n < num_threads) cond_main.wait(&mut);
cond.signal();
cond_main.wait(&mut);
try testing.expect(n == (num_threads - 1));
cond.broadcast();
while (n > 0) cond_main.wait(&mut);
try testing.expect(n == 0);
for (threads) |t| t.join();
}
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