pthreadmutex

pthread_mutex is a POSIX threads synchronization primitive used to control access to shared data in multi-threaded programs. A mutex (mutual exclusion) allows only one thread at a time to execute a critical section protected by the mutex, preventing data races.

Usage: The mutex object can be statically initialized with PTHREAD_MUTEX_INITIALIZER or dynamically with pthread_mutex_init, which accepts a mutex attribute object. Operations include pthread_mutex_lock to acquire, pthread_mutex_trylock to attempt without blocking, pthread_mutex_unlock to release, and pthread_mutex_destroy when finished. If a thread attempts to lock a mutex already owned by another thread, behavior depends on the mutex type; blocking lock will wait until ownership is released, while trylock returns EBUSY.

Mutex types and attributes: The type is defined by pthread_mutexattr_t. Standard types include PTHREAD_MUTEX_NORMAL, PTHREAD_MUTEX_ERRORCHECK, PTHREAD_MUTEX_RECURSIVE, and PTHREAD_MUTEX_DEFAULT. Normal type may lead to undefined behavior if a thread attempts to relock the mutex it already holds; error-check type detects such errors and may return an error; recursive type allows the owning thread to acquire the same mutex multiple times and requires the same number of unlocks. The default type is implementation-defined and may be equivalent to one of the others. Additional attributes support robustness (PTHREAD_MUTEX_ROBUST) and priority handling (PTHREAD_PRIO_INHERIT, PTHREAD_PRIO_PROTECT).

Notes: The mutex must be unlocked by the thread that holds it; unlocking by a non-owner yields undefined behavior for normal and error-checking types, while robust types provide recovery semantics. Deadlocks can occur if multiple threads hold multiple mutexes in conflicting orders.

See also: pthread_spinlock, pthread_cond, pthread_rwlock.