Thread Deadlock Issues

-(void) viewdidload {[Super viewdidload];    NSLog (@ "1");    Dispatch_sync (Dispatch_get_main_queue (), ^{NSLog (@ "2");    }); NSLog (@ "3");} What will it output and whyAnswer:Output 1,Use Dispatch_sync (Dispatch_get_main_queue () ^ () {block body}) in iOS;

Dispath adds a synchronized block to the home team;

At this point the home queue is waiting for Dispatch_sync (Dispatch_get_main_queue (), ^ () {block Body}), and the execution

The Dispatch_sync is waiting for the home queue to finish executing.

thereby causing a deadlock.

So you should use asynchronous execution when iOS uses the primary queue Dispatch_get_main_queue ()

Dispatch_Async(Dispatch_get_main_queue (), ^ () {

NSLog (@ "2");

});

Conclusion: Dispatch_sync

Will call the Dispatch_sync line routines and so on the contents of Dispatch_sync, and then continue to execute.

Dispatch_async

The thread that calls Dispatch_async does not have to wait for dispatch_async content to continue executing itself.

Dispatch_sync/async (Dispatch_get_main_queue (), ^ () {Block Body})

Just add the block to the queue. Sequence of execution in order of queue

The difference between sync/async is whether the thread that calls Diapatch waits for dispatch to finish executing.

Thread Deadlock Issues