pthread_rwlock_rdlock(3) - NetBSD Manual Pages

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PTHREAD_RWLOCK_RDLOC... NetBSD Library Functions ManualPTHREAD_RWLOCK_RDLOC...


NAME

     pthread_rwlock_rdlock, pthread_rwlock_timedrdlock,
     pthread_rwlock_tryrdlock -- acquire a read/write lock for reading


LIBRARY

     POSIX Threads Library (libpthread, -lpthread)


SYNOPSIS

     #include <pthread.h>

     int
     pthread_rwlock_rdlock(pthread_rwlock_t *lock);

     int
     pthread_rwlock_timedrdlock(pthread_rwlock_t * restrict lock,
         const struct timespec * restrict abstime);

     int
     pthread_rwlock_tryrdlock(pthread_rwlock_t *lock);


DESCRIPTION

     The pthread_rwlock_rdlock() function acquires a read lock on lock pro-
     vided that lock is not presently held for writing and no writer threads
     are presently blocked on the lock.  If the read lock cannot be immedi-
     ately acquired, the calling thread blocks until it can acquire the lock.

     The pthread_rwlock_timedrdlock() performs the same action, but will not
     wait beyond abstime to obtain the lock before returning.

     The pthread_rwlock_tryrdlock() function performs the same action as
     pthread_rwlock_rdlock(), but does not block if the lock cannot be immedi-
     ately obtained (i.e., the lock is held for writing or there are waiting
     writers).

     A thread may hold multiple concurrent read locks.  If so,
     pthread_rwlock_unlock() must be called once for each lock obtained.

     The results of acquiring a read lock while the calling thread holds a
     write lock are undefined.


RETURN VALUES

     If successful, the pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(),
     and pthread_rwlock_tryrdlock() functions will return zero.  Otherwise an
     error number will be returned to indicate the error.


ERRORS

     The pthread_rwlock_tryrdlock() function shall fail if:

     [EBUSY]            The lock could not be acquired because a writer holds
                        the lock or was blocked on it.

     The pthread_rwlock_timedrdlock() function shall fail if:

     [ETIMEDOUT]        The time specified by abstime was reached before the
                        lock could be obtained.

     The pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), and
     pthread_rwlock_tryrdlock() functions may fail if:

     [EAGAIN]           The lock could not be acquired because the maximum
                        number of read locks against lock has been exceeded.

     [EDEADLK]          The current thread already owns lock for writing.

     [EINVAL]           The value specified by lock is invalid.


SEE ALSO

     pthread_rwlock_destroy(3), pthread_rwlock_init(3),
     pthread_rwlock_unlock(3), pthread_rwlock_wrlock(3)


STANDARDS

     pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), and
     pthread_rwlock_tryrdlock() conform to ISO/IEC 9945-1:1996 (``POSIX.1'').

NetBSD 5.1.2                   January 30, 2003                   NetBSD 5.1.2