What's the difference between "mutex" and "lock"?

A mutex is a synchronization object. You acquire a lock on a mutex at the beginning of a section of code, and release it at the end, in order to ensure that no other thread is accessing the same data at the same time. A mutex typically has a lifetime equal to that of the data it is protecting, and that one mutex is accessed by multiple threads.

A lock object is an object that encapsulates that lock. When the object is constructed it acquires the lock on the mutex. When it is destructed the lock is released. You typically create a new lock object for every access to the shared data.

A mutex is an object which can be locked. A lock is the object whichmaintains the lock. To create a lock, you need to pass it a mutex.

Locks can provide mutual exclusion but not condition synchronization.Unlike a semaphore, a lock has an owner, and ownership plays an importantrole in the behavior of a lock

example -

class lockableObject { public void F() {mutex.lock(); ...; mutex.unlock();}public void G() {mutex.lock(); ...; F(); ...; mutex.unlock();}private mutexLock mutex; }// method G() calls method F()

Lock mutex in class lockableObject is used to turn methods F() and G() into critical sections. Thus, only one thread at a time can execute inside a method of a lockableObject. When a thread calls method G(), the mutex is locked. When method G() calls method F(), mutex.lock() is executed in F(), but the calling thread is not blocked since it already owns mutex. If mutex were a binary semaphore instead of a lock, the call from G() to F() would block the calling thread when mutex.P() was executed in F(). (Recall that comple- tions of P() and V() operations on a binary semaphore must alternate.) This would create a deadlock since no other threads would be able execute inside F() or G().

These are differences between locks and binary semaphores:1 For a binary semaphore,if two calls are made toP()without any intervening call to V(), the second call will block. But a thread that owns a lock and requests ownership again is not blocked. (Beware of the fact that locks are not always recursive, so check the documentation before using a lock.)2 The owner for successive calls to lock() and unlock() must be the same thread. But successive calls to P () and V () can be made by different threads.