A mutex, short for mutual exclusion lock, is a synchronization primitive for avoiding data races. A thread that needs to enter a critical section is first locking the mutex (locking is sometimes also called acquiring a mutex lock). This means that no other thread can lock the same mutex until the first thread that holds the lock has unlocked the mutex. In that way, the mutex guarantees that only one thread at a time is inside a critical section.
In the following figure, we can see how the example of the race condition can be avoided by using a mutex. The instruction labeled L is a lock instruction and the instruction labeled U is an unlock instruction. The first thread executing on Core 0 reaches the critical section first and locks ...
