Advanced Mac OS X Programming: The Big Nerd Ranch Guide

For the More Curious: Read/Write Locks

Both Cocoa and pthreads provide read/write locks. These allow a data structure to be read by a number of readers simultaneously but only allow one thread write access at a time.

pthread_rwlock_t works just like pthread_mutex_t but with a couple of extra calls. Here are the details:

pthread_rwlock_init (pthread_rwlock_t *lock,
                     const pthread_rwlockattr_t *attr);

OS X does not define PTHREAD_RWLOCK_INITIALIZER, so you cannot create them statically.

int pthread_rwlock_destroy (pthread_rwlock_t *lock);

Rather than use lock(), you specify which kind of locking you want:

• int pthread_rwlock_rdlock (pthread_rwlock_t *rwlock);

• int pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock);

• int pthread_rwlock_wrlock (pthread_rwlock_t ...