pthread_rwlock_rdlock - Acquires a read-write lock for
pthread_rwlock_t *rwlock );
DECthreads POSIX 1003.1c Library (libpthread.so)
Address of the read-write lock object to acquire for read
This routine acquires a read-write lock for read access.
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. If a thread already holds the lock for
read access, the lock is granted 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 corresponding 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 interrupt routine 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
lock for read access could not be acquired because the
maximum number of read lock acquisitions for rwlock has
been exceeded. The current thread already owns the readwrite
lock for writing. The value specified by rwlock
does not refer to an initialized read-write lock object.
Functions: pthread_rwlock_init(3), pthread_rwlockattr_init(3), pthread_rwlock_tryrdlock(3),
Manuals: Guide to DECthreads and Programmer's Guide
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