GNU Objective-C provides support for synchronized blocks:
@synchronized (ObjCClass *guard) {
…
}
Upon entering the @synchronized block, a thread of execution
shall first check whether a lock has been placed on the corresponding
guard object by another thread. If it has, the current thread
shall wait until the other thread relinquishes its lock. Once
guard becomes available, the current thread will place its own
lock on it, execute the code contained in the @synchronized
block, and finally relinquish the lock (thereby making guard
available to other threads).
Unlike Java, Objective-C does not allow for entire methods to be
marked @synchronized. Note that throwing exceptions out of
@synchronized blocks is allowed, and will cause the guarding
object to be unlocked properly.
Because of the interactions between synchronization and exception
handling, you can only use @synchronized when compiling with
exceptions enabled, that is with the command line option
-fobjc-exceptions.