iOS 中的 @synchronize(self)
The Objective-C language level synchronization uses the mutex, just like NSLock
does. 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 particular with an NSLock
you have an explicit lock whereas with @synchronize
you 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 issues, but mechanically they behave basically the same.
You can think of @synchronize
as basically a compiler rewrite:
- (NSString *)myString {
@synchronized(self) {
return [[myString retain] autorelease];
}
}
is transformed into:
- (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 should get the point across.