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//! A semaphore is an unsigned integer that blocks the kernel thread if
//! the number would become negative.
//! This API supports static initialization and does not require deinitialization.
mutex: Mutex = .{},
cond: Condition = .{},
/// It is OK to initialize this field to any value.
permits: usize = 0,
const Semaphore = @This();
const std = @import("../std.zig");
const Mutex = std.Thread.Mutex;
const Condition = std.Thread.Condition;
const builtin = @import("builtin");
const testing = std.testing;
pub fn wait(sem: *Semaphore) void {
sem.mutex.lock();
defer sem.mutex.unlock();
while (sem.permits == 0)
sem.cond.wait(&sem.mutex);
sem.permits -= 1;
if (sem.permits > 0)
sem.cond.signal();
}
pub fn post(sem: *Semaphore) void {
sem.mutex.lock();
defer sem.mutex.unlock();
sem.permits += 1;
sem.cond.signal();
}
test "Thread.Semaphore" {
if (builtin.single_threaded) {
return error.SkipZigTest;
}
const TestContext = struct {
sem: *Semaphore,
n: *i32,
fn worker(ctx: *@This()) void {
ctx.sem.wait();
ctx.n.* += 1;
ctx.sem.post();
}
};
const num_threads = 3;
var sem = Semaphore{ .permits = 1 };
var threads: [num_threads]std.Thread = undefined;
var n: i32 = 0;
var ctx = TestContext{ .sem = &sem, .n = &n };
for (threads) |*t| t.* = try std.Thread.spawn(.{}, TestContext.worker, .{&ctx});
for (threads) |t| t.join();
sem.wait();
try testing.expect(n == num_threads);
}
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