Question

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objective-c : @synchronized, how does it work?

when i have three methods:

    -(void)  a {
        @synchronized(self) {
          //part a
        }
     }

    -(void) b {
         @synchronized(self) {
          //part b 
     }

   -(void) c {
        // part c
    }

and thread is in part a , then will be part c blocked for other threads?

Answer 1

Only @synchronized blocks interact with each other. As long as one thread is executing either part A or part B, no other thread can enter part A or part B. Part C is not affected by this in any way.

Your new comment above made a bit clearer, what you are actually asking.

In @synchronized(self), self is not the thing that is locked itself, it is used as a lock to guarantee that only one thread at a time can enter the @synchronized block.

As the official documentation explains: you can use any object as a semaphore.

The chapter on synchronization has a comprehensive description of all available locking options, btw.