diff --git a/lib/std/Thread/Mutex/Recursive.zig b/lib/std/Thread/Mutex/Recursive.zig index 707b67f105..d6d90ed648 100644 --- a/lib/std/Thread/Mutex/Recursive.zig +++ b/lib/std/Thread/Mutex/Recursive.zig @@ -30,7 +30,13 @@ pub const init: Recursive = .{ /// Otherwise, returns `true` and the caller should `unlock()` the Mutex to release it. pub fn tryLock(r: *Recursive) bool { const current_thread_id = std.Thread.getCurrentId(); - return tryLockInner(r, current_thread_id); + if (@atomicLoad(std.Thread.Id, &r.thread_id, .unordered) != current_thread_id) { + if (!r.mutex.tryLock()) return false; + assert(r.lock_count == 0); + @atomicStore(std.Thread.Id, &r.thread_id, current_thread_id, .unordered); + } + r.lock_count += 1; + return true; } /// Acquires the `Mutex`, blocking the current thread while the mutex is @@ -42,12 +48,12 @@ pub fn tryLock(r: *Recursive) bool { /// of whether the lock was already held by the same thread. pub fn lock(r: *Recursive) void { const current_thread_id = std.Thread.getCurrentId(); - if (!tryLockInner(r, current_thread_id)) { + if (@atomicLoad(std.Thread.Id, &r.thread_id, .unordered) != current_thread_id) { r.mutex.lock(); assert(r.lock_count == 0); - r.lock_count = 1; - @atomicStore(std.Thread.Id, &r.thread_id, current_thread_id, .monotonic); + @atomicStore(std.Thread.Id, &r.thread_id, current_thread_id, .unordered); } + r.lock_count += 1; } /// Releases the `Mutex` which was previously acquired with `lock` or `tryLock`. @@ -57,30 +63,10 @@ pub fn lock(r: *Recursive) void { pub fn unlock(r: *Recursive) void { r.lock_count -= 1; if (r.lock_count == 0) { - // Prevent race where: - // * Thread A obtains lock and has not yet stored the new thread id. - // * Thread B loads the thread id after tryLock() false and observes stale thread id. - @atomicStore(std.Thread.Id, &r.thread_id, invalid_thread_id, .seq_cst); + @atomicStore(std.Thread.Id, &r.thread_id, invalid_thread_id, .unordered); r.mutex.unlock(); } } -fn tryLockInner(r: *Recursive, current_thread_id: std.Thread.Id) bool { - if (r.mutex.tryLock()) { - assert(r.lock_count == 0); - r.lock_count = 1; - @atomicStore(std.Thread.Id, &r.thread_id, current_thread_id, .monotonic); - return true; - } - - const locked_thread_id = @atomicLoad(std.Thread.Id, &r.thread_id, .monotonic); - if (locked_thread_id == current_thread_id) { - r.lock_count += 1; - return true; - } - - return false; -} - /// A value that does not alias any other thread id. -const invalid_thread_id: std.Thread.Id = 0; +const invalid_thread_id: std.Thread.Id = std.math.maxInt(std.Thread.Id);