PTHREAD_MUTEXATTR(3)

PTHREAD_MUTEXATTR(3) | Library Functions Manual | PTHREAD_MUTEXATTR(3)

# NAME

pthread_mutexattr_init, pthread_mutexattr_destroy, pthread_mutexattr_settype, pthread_mutexattr_gettype — mutex attribute operations

# LIBRARY

POSIX Threads Library (libpthread, -lpthread)

# SYNOPSIS

#include <pthread.h>

int
pthread_mutexattr_init(pthread_mutexattr_t *attr);

int
pthread_mutexattr_destroy(pthread_mutexattr_t *attr);

int
pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);

int
pthread_mutexattr_gettype(pthread_mutexattr_t * restrict attr, int * restrict type);

# DESCRIPTION

Mutex attributes are used to specify parameters to pthread_mutex_init(). Like with thread attributes, one attribute object can be used in multiple calls to pthread_mutex_init(3), with or without modifications between calls.

The pthread_mutexattr_init() function initializes attr with all the default mutex attributes.

The pthread_mutexattr_destroy() function destroys attr.

The pthread_mutexattr_settype() functions set the mutex type value of the attribute. Valid mutex types are:

PTHREAD_MUTEX_NORMAL
  This type of mutex does not check for usage errors. It will deadlock if reentered, and result in undefined behavior if a locked mutex is unlocked by another thread. Attempts to unlock an already unlocked PTHREAD_MUTEX_NORMAL mutex will result in undefined behavior.
PTHREAD_MUTEX_ERRORCHECK
  These mutexes do check for usage errors. If an attempt is made to relock a PTHREAD_MUTEX_ERRORCHECK mutex without first dropping the lock, an error will be returned. If a thread attempts to unlock a PTHREAD_MUTEX_ERRORCHECK mutex that is locked by another thread, an error will be returned. If a thread attempts to unlock a PTHREAD_MUTEX_ERRORCHECK thread that is unlocked, an error will be returned.
PTHREAD_MUTEX_RECURSIVE
  These mutexes allow recursive locking. An attempt to relock a PTHREAD_MUTEX_RECURSIVE mutex that is already locked by the same thread succeeds. An equivalent number of pthread_mutex_unlock(3) calls are needed before the mutex will wake another thread waiting on this lock. If a thread attempts to unlock a PTHREAD_MUTEX_RECURSIVE mutex that is locked by another thread, an error will be returned. If a thread attempts to unlock a PTHREAD_MUTEX_RECURSIVE thread that is unlocked, an error will be returned.

  It is advised that PTHREAD_MUTEX_RECURSIVE mutexes are not used with condition variables. This is because of the implicit unlocking done by pthread_cond_wait(3) and pthread_cond_timedwait(3).

PTHREAD_MUTEX_DEFAULT
  Also this type of mutex will cause undefined behavior if reentered. Unlocking a PTHREAD_MUTEX_DEFAULT mutex locked by another thread will result in undefined behavior. Attempts to unlock an already unlocked PTHREAD_MUTEX_DEFAULT mutex will result in undefined behavior.

  This is the default mutex type for pthread_mutexaddr_init().

The pthread_mutexattr_gettype() functions copy the type value of the attribute to the location pointed to by the second parameter.

# RETURN VALUES

If successful, these functions return 0. Otherwise, an error number is returned to indicate the error.

# ERRORS

The pthread_mutexattr_init() function shall fail if:

[ENOMEM]
  Insufficient memory exists to initialize the mutex attributes object.

The pthread_mutexattr_settype() function shall fail if:

[EINVAL]
  The value specified either by type or attr is invalid.

No error numbers are defined for the pthread_mutexattr_destroy() and pthread_mutexattr_gettype() functions.

# SEE ALSO

pthread_mutex_init(3)

# STANDARDS

These functions conform to IEEE Std 1003.1-2001 (“POSIX.1”).

July 9, 2010 | NetBSD 7.1