@ Synchronize (self) in iOS)

The Objective-C language level synchronization uses the mutex, just likeNSLockDoes. Semantically there are some small technical differences, but it is basically correct to think of them as two seperate interface implemented on top of a common (more primitive) entity.

In particle withNSLockYou have an explicit lock whereas@synchronizeYou have an implicit lock associated with the object you are using to synchronize. the benefit of the language level locking is the compiler understands it so it can deal with scoping the issues, but mechanically they behave basically The same.

You can think@synchronizeAs basically a compiler rewrite:

- (NSString *)myString {
  @synchronized(self) {
    return [[myString retain] autorelease];
  }
}

Is transformed:

- (NSString *)myString {
  NSString *retval = nil;
  pthread_mutex_t *self_mutex = LOOK_UP_MUTEX(self);
  pthread_mutex_lock(self_mutex);
  retval = [[myString retain] autorelease];
  pthread_mutex_unlock(self_mutex);
  return retval;
}

That is not exactly correct because the actual transform is more complex and uses recursive locks, but it shocould get the point authentication ss.