Thread

1. When several threads compete for a mutex, the losers block at that call - an unblocking call is available with "trylock" instead of the "lock" call.

2. In subroutines that execute to completion normally, you can often dispense with calling pthread_exit() - unless, of course, you want to pass a return code back. However, in main(), there is a definite problem if main() completes before the threads it spawned. If you don't call pthread_exit()explicitly, when main() completes, the process (and all threads) will be terminated. By calling pthread_exit() in main(), the process and all of its threads will be kept alive even though all of the code in main() has been executed

3. pthread_exit is used to explicitly exit a thread. Typically, the pthread_exit() routine is called after a thread has completed its work and is no longer required to exist.

4. If main() finishes before the threads it has created, and exits with pthread_exit(), the other threads will continue to execute. Otherwise, they will be automatically terminated when main() finishes.

5. The attr object is used to establish properties for the mutex object, and must be of type pthread_mutexattr_t if used (may be specified as NULL to accept defaults). The Pthreads standard defines three optional mutex attributes:

• Protocol: Specifies the protocol used to prevent priority inversions for a mutex.
• Prioceiling: Specifies the priority ceiling of a mutex.
• Process-shared: Specifies the process sharing of a mutex.