PTHREAD_MUTEX(3)

NAME
pthread_mutex - mutual exclusion primitives

LIBRARY
libpthread

SYNOPSIS
#include <pthread.h>
int
pthread_mutex_init(pthread_mutex_t * restrict mutex, const pthread_mutexattr_t * restrict attr);
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
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);
int
pthread_mutex_timedlock(pthread_mutex_t *__restrict mutex, const struct timespec *__restrict timeout);
int
pthread_mutex_getprioceiling(const pthread_mutex_t * __restrict mutex, int * __restrict prioceiling);
int
pthread_mutex_setprioceiling(pthread_mutex_t * __restrict mutex, int prioceiling, int * __restrict old_ceiling);

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 statically 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 undefined 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 available. 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.

The pthread_mutex_timedlock() function shall lock the mutex object referenced by mutex. If the mutex is already locked, the calling thread shall block until the mutex becomes available in the pthread_mutex_lock() function. If the mutex cannot be locked without waiting for another thread to unlock the mutex, this wait shall be terminated when the specified timeout expires. The timeout shall expire when the absolute time specified by timeout passes, as measured by the clock on which timeouts are based.

The pthread_mutex_getprioceiling() function shall return the current priority ceiling of the mutex.

The pthread_mutex_setprioceiling() function shall either lock the mutex if it is unlocked, or block until it can sucessfully lock the mutex, then it shall change the mutex's priority ceiling and release the mutex. When the change is successful, the previous value of the priority ceiling shall be returned in old_ceiling. The process of locking the mutex need not adhere to the priority protect protocol. If pthread_mutex_setprioceiling() function fails, the mutex priority ceiling shall not be changed.

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.

pthread_mutex_timedlock() may fail if:

[EINVAL]
    The mutex was created with the protocol attribute having the value PTHREAD_PRIO_PROTECT and the calling thread's priority is higher than the mutex current priority ceiling; or the process or thread would have blocked, and the timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.

[ETIMEDOUT]
    The mutex could not be locked before the specified timeout expired.

The pthread_mutex_getprioceiling() and pthread_mutex_setprioceiling() functions may fail if:

[EINVAL]
    The priority requested by prioceiling is out of range; or the value specified by mutex does not refer to a currently existing mutex.

[EPERM]
    The caller does not have the privilege to perform the operation.

SEE ALSO
pthread(3), pthread_barrier(3), pthread_cond(3), pthread_mutexattr(3), pthread_rwlock(3), pthread_spin(3)

STANDARDS
These functions conform to p1003.1-2001.