c - What is the `pthread_mutex_lock()` wake order with multiple threads waiting?

Question

Suppose I have multiple threads blocking on a call to pthread_mutex_lock(). When the mutex becomes available, does the first thread that called pthread_mutex_lock() get the lock? That is, are calls to pthread_mutex_lock() in FIFO order? If not, what, if any, order are they in? Thanks!

Answer 1

When the mutex becomes available, does the first thread that called pthread_mutex_lock() get the lock?

No. One of the waiting threads gets a lock, but which one gets it is not determined.

FIFO order?

FIFO mutex is rather a pattern already. See Implementing a FIFO mutex in pthreads