pthread_rwlock_rdlock - Acquires a read-write lock for read access.
DECthreads POSIX 1003.1c Library (libpthread.so)
Address of the read-write lock object to acquire for read access.
This routine acquires a read-write lock for read access. If a thread already holds the lock for read access, the lock is granted and this routine returns. If no thread already holds the lock for write access and there are no writers waiting to acquire the lock, the lock for read access is granted to the calling thread and this routine returns.
A thread can hold multiple, concurrent locks for read access on the same read-write lock. In a given thread, for each call to this routine that successfully acquires the same read-write lock for read access, a corrresponding call to pthread_rwlock_unlock must be issued.
If some thread already holds the lock for write access, the calling thread will not acquire the read lock. If the read lock is not acquired, the calling thread blocks until it can acquire the lock for read access. Results are undefined if the calling thread has already acquired a lock for write access on rwlock when this routine is called.
If the read-write lock object referenced by rwlock is not initialized, the results of calling this routine are undefined.
If a thread is interrupted (via a Tru64 UNIX signal or an OpenVMS AST) while waiting for a read-write lock for read access, upon return from the signal handler the thread resumes waiting for the lock as if it had not been interrupted.
If an error condition occurs, this routine returns an integer value indicating the type of error. Possible return values are as follows: Successful completion. The value specified by rwlock does not refer to an initialized read-write lock object. The current thread already owns the read-write lock for writing. The lock for read access could not be acquired because the maximum number of read lock acquisitions for rwlock has been exceeded.
Functions: pthread_rwlock_init(3), pthread_rwlockattr_init(3), pthread_rwlock_tryrdlock(3), pthread_rwlock_wrlock(3), pthread_rwlock_unlock(3)
Manuals: Guide to DECthreads and Programmer's Guide