pthreadmutext

pthread mutex, short for POSIX threads mutual exclusion, is a synchronization primitive used to protect shared data from concurrent access in multi-threaded programs. The mutex type is typically declared as pthread_mutex_t and can be created with a static initializer or dynamically with pthread_mutex_init. A corresponding destructor, pthread_mutex_destroy, releases resources when the mutex is no longer needed. Some attributes can be set via pthread_mutexattr_t to customize behavior.

Locking a mutex is done with pthread_mutex_lock, which blocks the calling thread until the mutex becomes available. If the mutex is already held by another thread, the requesting thread waits. Non-blocking attempts are possible with pthread_mutex_trylock, which returns immediately if the mutex is unavailable. Some systems support a timed variant, pthread_mutex_timedlock, allowing a wait with a timeout.

Mutexes can have different types defined by the pthread_mutexattr_t attributes. Common types include PTHREAD_MUTEX_NORMAL, which offers no deadlock detection and can lead to deadlocks if a thread attempts to relock it; PTHREAD_MUTEX_RECURSIVE, which allows the same thread to acquire the mutex multiple times; and PTHREAD_MUTEX_ERRORCHECK, which provides error checking for incorrect usage and can return error codes on reclaims. Implementations may also provide adaptive or other specialized variants.

Correct usage requires holding the mutex while accessing the protected data and releasing it as soon as the critical section ends. Improper use can cause deadlocks, priority inversion, or reduced concurrency. In addition to basic locking, programs may employ robust mutexes to handle thread termination gracefully, and ensure proper destruction to avoid resource leaks.

Overall, pthread mutexes are a fundamental tool in applying mutual exclusion in POSIX-compliant multi-threaded software, balancing safety and performance through choice of type and attributes.