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().
     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
     ISO/IEC 9945-1:1996 (``POSIX.1'').

NetBSD 5.1                     January 30, 2003                     NetBSD 5.1