#include <pthread.h> int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock );
pthread_rwlock_wrlock(3THR) applies a write lock to the read-write lock referenced by rwlock. The calling thread acquires the write lock if no other thread (reader or writer) holds the read-write lock rwlock. Otherwise, the thread blocks (that is, does not return from the pthread_rwlock_wrlock() call) until it can acquire the lock. Results are undefined if the calling thread holds the read-write lock (whether a read or write lock) at the time the call is made.
Implementations are allowed to favor writers over readers to avoid writer starvation. (For instance, the Solaris threads implementation favors writers over readers. See rw_wrlock(3THR).)
Results are undefined if pthread_rwlock_wrlock() is called with an uninitialized read-write lock.
If a signal is delivered to a thread waiting for a read-write lock for writing, upon return from the signal handler the thread resumes waiting for the read-write lock for writing as if it was not interrupted.
pthread_rwlock_rwlock() returns zero if the lock for writing on the read-write lock object referenced by rwlock is acquired. Otherwise an error number is returned to indicate the error.