grand-central-dispatch

-(void)viewDidLoad{ dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ [NSTimer scheduledTimerWithTimeInterval:0.10 target:self selector:@selector(action_Timer) userInfo:nil repeats:YES]; } ); } -(void)action_Timer{ LOG("Timer called"); } action_Timer is not being called. I dont know why. Do you have any idea? You're calling +[NSTimer scheduledTimerWithTimeInterval:...] from a GCD worker thread. GCD worker threads don't run a run loop. That's why your first try didn't work. When you tried [[NSRunLoop mainRunLoop] addTimer:myTimer forMode:NSDefaultRunLoopMode] ,

As a programming exercise, I just finished writing a Sudoku solver that uses the backtracking algorithm (see Wikipedia for a simple example written in C). To take this a step further, I would like to use Snow Leopard's GCD to parallelize this so that it runs on all of my machine's cores. Can someone give me pointers on how I should go about doing this and what code changes I should make? Thanks! Matt For one, since backtracking is a depth-first search it is not directly parallelizable, since any newly computed result cannot be used be directly used by another thread. Instead, you must divide

Using XCode-8.2.1, Swift-3.0.2 and iOS-10.2.1, I am trying to call two different URLSession.shared.dataTasks (the first is a simple URL-request and the second is a POST-request). Since my first dataTask delivers a result that is needed in the httpBody of the second dataTask, the two URLSession.shared.dataTasks shall run in series, one after the other! (and also the preparative code shall run consecutively). I tried, so far, using two consecutive serialQueue.sync{} queues. But I had to realize that the code does not perform in the order I would like to. The print-statement in the log turn out

When a user creates a new group in my app I have to push invites to the database as well as other information. I've started using Dispatch Groups in order to keep track of when all the information is successfully sent out so I can dismiss the view. I'm trying to use a dispatch group for the invites and another dispatch group for all the data. Here's what I have: // Push new data to db func createGroup(onSccess completion:@escaping () -> Void) { let inviteDispatchGroup = DispatchGroup() let dataDispatchGroup = DispatchGroup() let uid = FIRAuth.auth()?.currentUser?.uid let name = String(uid!) +

I have a property @property NSLock *myLock And I want to write two methods: - (void) lock and - (void) unlock These methods lock and unlock myLock respectively and they need to do this regardless of what thread or queue called them. For instance, thread A might have called lock but queue B might be the one calling unlock . Both of these methods should work appropriately without reporting that I am trying to unlock a lock from a different thread/queue that locked it. Additionally, they need to do this synchronously. It is rare anymore that NSLock is the right tool for the job. There much better

I'm fairly new to GCD and was trying to find an answer to this. Assuming I have the following code: dispatch_queue_t queue = dispatch_queue_create("queue", NULL); dispatch_async(queue, ^{ // do some stuff }); Where in the code should I release the queue? Inside or outside the block? Outside the block. I'm fairly certain you don't have to wait for the async block to finish as GCD will retain the queue. 来源： https://stackoverflow.com/questions/4842460/when-to-dispatch-release