DISPATCH_SOURCE_TYPE_READ : file descriptor를 모니터한다.

	dispatch_queue_t globalQueue  =  dispatch_get_global_queue
									(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_source_t stdinSource
      = dispatch_source_create 	(	DISPATCH_SOURCE_TYPE_READ,
								STDIN_FILENO, //file descriptors
							        0,
								globalQueue );

    dispatch_source_set_event_handler (	stdinSource,
    	^{
    		char buf[1024];
        	int len = read(STDIN_FILENO, buf, sizeof(buf));
        	if(len > 0)
            	NSLog(@"Got data from stdin: %.*s", len, buf);
    	});

    dispatch_resume(stdinSource);