PTHREAD_MUTEX(3)

PTHREAD_MUTEX(3) | 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);

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);

# 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.

# 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”).

July 8, 2010 | NetBSD 7.1