Order of execution of waiting threads blocked by mutex
multithreading, mutex, windows
Solution
FIFO signaling leads to lock convoys. On newer versions of the Win32 API the convoy issue is addressed by macking mutexes and other synchrnonization primitives explicitly unfair (ie. no FIFO).
If more than one thread is waiting on a mutex, a waiting thread is selected. Do not assume a first-in, first-out (FIFO) order. External events such as kernel-mode APCs can change the wait order.
Problem
I have a mutex that controls access to a single object from multiple threads. When a thread has finished the mutex is unlocked to allow order threads to operate on the object. On Windows using the WaitForSingleObject function is there an order that threads are signaled? I want the first thread that attempts to lock the mutex to now be allowed to lock the mutex. This would be a FIFO queue so that signaling to the blocked threads is not random. Would I have to implement my own queuing mechanism to achieve this? And if so what functions are useful?