pthread_mutexattr(3) - NetBSD Manual Pages

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PTHREAD_MUTEXATTR(3)    NetBSD 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 dead-
            lock 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 unde-
            fined 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 unlock-
            ing done by pthread_cond_wait(3) and pthread_cond_timedwait(3).

       PTHREAD_MUTEX_DEFAULT
            Also this type of mutex will cause undefined behavior if reen-
            tered.  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 unde-
            fined 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'').

NetBSD 6.1.2                     July 9, 2010                     NetBSD 6.1.2