A mutex is the software equivalent of the lock on your toilet door. There is a zone in your code where only 1 thread at a time is allowed. So before entering,

A mutex is the software equivalent of the lock on your toilet door. There is a zone in your code where only 1 thread at a time is allowed. So before entering, you lock the mutex. Now either you are allowed in or are added to a set of waiters. When you leave, you unlock the mutex, and 1 other waiter is allowed to enter. This sounds easy, but is in practice wrought eith peril. You need high performance, not waste too much cpu time on sleepers, some notion of fairness when you have lots of waiters, minimal memory usage, etc...