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Number of threads waiting on a pthread mutex/rwlock
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PTHREAD_MUTEX(3) BSD Library Functions Manual PTHREAD_MUTEX(3) NAME
pthread_mutex -- mutual exclusion primitives LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> int pthread_mutex_init(pthread_mutex_t * restrict mutex, const pthread_mutexattr_t * restrict attr); int pthread_mutex_destroy(pthread_mutex_t *mutex); int pthread_mutex_lock(pthread_mutex_t *mutex); int pthread_mutex_trylock(pthread_mutex_t *mutex); int pthread_mutex_unlock(pthread_mutex_t *mutex); pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; DESCRIPTION
The pthread_mutex_init() function creates a new mutex, with attributes specified with attr. If attr is NULL, the default attributes are used. The macro PTHREAD_MUTEX_INITIALIZER can be used to initialize a mutex when the default attributes are appropriate and the mutex can be stati- cally allocated. The behavior is similar to pthread_mutex_init() with attr specified as NULL, except that no error checking is done. The pthread_mutex_destroy() function frees the resources allocated for mutex. It is possible to reinitialize a destroyed mutex, but unde- fined behavior may follow if the destroyed object is otherwise referenced. The pthread_mutex_lock() function locks mutex. If the mutex is already locked, the calling thread will block until the mutex becomes avail- able. The error conditions may vary depending on the type of the mutex; see pthread_mutexattr(3) for additional details. The pthread_mutex_trylock() function locks mutex. If the mutex is already locked, pthread_mutex_trylock() will not block waiting for the mutex, but will return an error condition. The pthread_mutex_unlock() function unlocks an acquired mutex. When operating with the default mutex type, undefined behavior follows if a thread tries to unlock a mutex that has not been locked by it, or if a thread tries to release a mutex that is already unlocked. RETURN VALUES
Upon success all described functions return zero. Otherwise, an error number will be returned to indicate the error. ERRORS
pthread_mutex_init() may fail if: [EAGAIN] The system lacks the resources to initialize another mutex. [EINVAL] The value specified by attr is invalid. [ENOMEM] The process cannot allocate enough memory to initialize another mutex. pthread_mutex_destroy() may fail if: [EBUSY] Mutex is locked by another thread. [EINVAL] The value specified by mutex is invalid. pthread_mutex_lock() may fail if: [EDEADLK] A deadlock would occur if the thread blocked waiting for mutex. [EINVAL] The value specified by mutex is invalid. pthread_mutex_trylock() may fail if: [EBUSY] Mutex is already locked. [EINVAL] The value specified by mutex is invalid. pthread_mutex_unlock() may fail if: [EINVAL] The value specified by mutex is invalid. [EPERM] The current thread does not hold a lock on mutex. SEE ALSO
pthread(3), pthread_barrier(3), pthread_cond(3), pthread_mutexattr(3), pthread_rwlock(3), pthread_spin(3) STANDARDS
These functions conform to IEEE Std 1003.1-2001 (``POSIX.1''). BSD
July 8, 2010 BSD
