#include <pthread.h> int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock );
The calling thread acquires the write lock if no other reader thread or writer thread holds the read-write lock rwlock. Otherwise, the thread blocks. The thread does not return from the pthread_rwlock_wrlock() call until the thread can acquire the lock. Results are undefined if the calling thread holds the read-write lock, either a read lock or write lock, at the time the call is made.
Implementations are allowed to favor writers over readers to avoid writer starvation. The Solaris implementation favors writers over readers.
Results are undefined if pthread_rwlock_wrlock() is called with an uninitialized read-write lock.
The thread signal handler processes a signal 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 the thread was not interrupted.