What is the difference between semaphore and mutex in implementation?

I read that mutex and binary semaphore are different in only one aspect, in the case of mu开发者_StackOverflow中文版tex the locking thread has to unlock, but in semaphore the locking and unlocking thread can be different?

Which one is more efficient?

Assuming you know the basic differences between a sempahore and mutex :

For fast, simple synchronization, use a critical section.

To synchronize threads across process boundaries, use mutexes.

To synchronize access to limited resources, use a semaphore.

Apart from the fact that mutexes have an owner, the two objects may be optimized for different usage. Mutexes are designed to be held only for a short time; violating this can cause poor performance and unfair scheduling. For example, a running thread may be permitted to acquire a mutex, even though another thread is already blocked on it, creating a deadlock. Semaphores may provide more fairness, or fairness can be forced using several condition variables.