#include <pthread.h>

     int
     pthread_rwlock_wrlock(pthread_rwlock_t *lock);

     int
     pthread_rwlock_trywrlock(pthread_rwlock_t *lock);

DESCRIPTION

     The pthread_rwlock_wrlock() function blocks until a write lock can be
     acquired against lock.  The pthread_rwlock_trywrlock() function performs
     the same action, but does not block if the lock cannot be immediately
     obtained.

     The results are undefined if the calling thread already holds the lock at
     the time the call is made.

IMPLEMENTATION NOTES

     To prevent writer starvation, writers are favored over readers.

RETURN VALUES

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

SEE ALSO

     pthread_rwlock_trywrlock(3), pthread_rwlock_unlock(3),
     pthread_rwlock_wrlock(3)

STANDARDS

     The pthread_rwlock_wrlock() and pthread_rwlock_trywrlock() functions are
     expected to conform to Version 2 of the Single UNIX Specification
     (``SUSv2'').

ERRORS

     The pthread_rwlock_trywrlock() function will fail if:

     [EBUSY]            The calling thread is not able to acquire the lock
                        without blocking.

     The pthread_rwlock_wrlock() and pthread_rwlock_trywrlock() functions may
     fail if:

     [EDEADLK]          The calling thread already owns the read/write lock
                        (for reading or writing).

     [EINVAL]           The value specified by lock is invalid.

     [ENOMEM]           Insufficient memory exists to initialize the lock
                        (applies to statically initialized locks only).

HISTORY