Question

What mechanisms does iOS provide to support multi-threading?

Answer 1

• NSThread creates a new low-level thread which can be started by calling the start method.

  NSThread* myThread = [[NSThread alloc] initWithTarget:self
                                         selector:@selector(myThreadMainMethod:)
                                         object:nil];
  [myThread start]; 

• NSOperationQueue allows a pool of threads to be created and used to execute NSOperations in parallel. NSOperations can also be run on the main thread by asking NSOperationQueue for the mainQueue.

  NSOperationQueue* myQueue = [[NSOperationQueue alloc] init];
  [myQueue addOperation:anOperation]; 
  [myQueue addOperationWithBlock:^{
    /* Do something. */
  }];

• GCD or Grand Central Dispatch is a modern feature of Objective-C that provides a rich set of methods and API's to use in order to support common multi-threading tasks. GCD provides a way to queue tasks for dispatch on either the main thread, a concurrent queue (tasks are run in parallel) or a serial queue (tasks are run in FIFO order).

  dispatch_queue_t myQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
  dispatch_async(myQueue, ^{
     printf("Do some work here.\n");
  });

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