PTHREAD_MUTEXATTR(3) BSD 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 behav-
ior.
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'').
BSD
July 9, 2010 BSD
