PTHREAD_MUTEXATTR(3)

NAME
pthread_mutexattr_init, pthread_mutexattr_destroy, pthread_mutexattr_settype, pthread_mutexattr_gettype - mutex attribute operations

LIBRARY
libpthread

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(). One attribute object can be used in multiple calls to pthread_mutex_init(), 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, PTHREAD_MUTEX_ERRORCHECK, PTHREAD_MUTEX_RECURSIVE, and PTHREAD_MUTEX_DEFAULT. The default mutex type for pthread_mutexaddr_init() is PTHREAD_MUTEX_DEFAULT.

PTHREAD_MUTEX_NORMAL mutexes do not check for usage errors. PTHREAD_MUTEX_NORMAL mutexes 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 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 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.

PTHREAD_MUTEX_DEFAULT mutexes result in 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.

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
pthread_mutexattr_init() shall fail if:

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

pthread_mutexattr_settype() shall fail if:

[EINVAL]
    The value specified by type is invalid.

pthread_mutexattr_destroy(), pthread_mutexattr_settype(), and pthread_mutexattr_gettype() may fail if:

[EINVAL]
    Invalid value for attr.

SEE ALSO
pthread_mutex_init(3)

STANDARDS
pthread_mutexattr_init(), pthread_mutexattr_destroy(), pthread_mutexattr_settype(), and pthread_mutexattr_gettype() conform to p1003.1-96.