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”).