pthread_rwlock_wrlock - Acquires a read-write lock for write access.
DECthreads POSIX 1003.1c Library (libpthread.so)
Address of the read-write lock object to acquire for write access.
This routine attempts to acquire a read-write lock for write access. If any thread already has acquired the lock for write access or read access, the lock is not granted and the calling thread blocks until it can acquire the lock. A thread can hold only one lock for write access on a read-write lock.
Results are undefined if the calling thread holds the read-write lock (whether for read or write access) at the time 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 write access, upon return from the signal handler the thread resumes waiting for the lock as if it had not been interrupted.
Realtime applications can encounter priority inversion when using read-write locks. The problem occurs when a high-priority thread acquires a read-write lock that is about to be unlocked (that is, posted) by a low-priority thread, but the low-priority thread is preempted by a medium-priority thread. This scenario leads to priority inversion in that a high-priority thread is blocked by lower-priority threads for an unlimited period of time. During system design, realtime programmers must take into account the possibility of priority inversion and can deal with it in a number of ways, such as by having critical sections that are guarded by read-write locks execute at a high priority, so that a thread cannot be preempted while executing in its critical section.
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 write or read access.
Functions: pthread_rwlock_init(3), pthread_rwlockattr_init(3), pthread_rwlock_rdlock(3), pthread_rwlock_trywrlock(3), pthread_rwlock_unlock(3)
Manuals: Guide to DECthreads and Programmer's Guide