Assign whatever identifier you want using dispatch_queue_set_specific(). You can then check your identifier using dispatch_get_specific(). Remember that dispatch_get_specific() is nice because it’ll start at the current queue, and then walk up the target queues if the key isn’t set on the current one. This usually doesn’t matter, but can be useful in some cases.
You use it when you want to execute a block and wait for the results. One example of this is the pattern where you’re using a dispatch queue instead of locks for synchronization. For example, assume you have a shared NSMutableArray a, with access mediated by dispatch queue q. A background thread might be appending … Read more
Try this one it’s Working code (Swift 4). func NKPlaceholderImage(image:UIImage?, imageView:UIImageView?,imgUrl:String,compate:@escaping (UIImage?) -> Void){ if image != nil && imageView != nil { imageView!.image = image! } var urlcatch = imgUrl.replacingOccurrences(of: “https://stackoverflow.com/”, with: “#”) let documentpath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] urlcatch = documentpath + “https://stackoverflow.com/” + “\(urlcatch)” let image = UIImage(contentsOfFile:urlcatch) if image != nil … Read more
You say: From what I understand the setup here is: self —> queue self <— block The queue is merely a shell/wrapper for the block. Which is why even if I nil the queue, the block will continue its execution. They’re independent. The fact that self happens to have a strong reference to the queue … Read more
You’re missing some basics about asynchronous development with blocks. You can’t have a dispatched block return from anywhere but its own scope. Think of each block as its own method, instead of inline code. I think what you’re looking for is something similar to this… – (void)testWithHandler:(void(^)(int result))handler { [obj somemethodwithcompeltionblock:^{ int someInt = 10; … Read more
Since Swift 1.x, Swift has been using dispatch_once behind the scenes to perform thread-safe lazy initialization of global variables and static properties. So the static var above was already using dispatch_once, which makes it sort of weird (and possibly problematic to use it again as a token for another dispatch_once. In fact there’s really no … Read more
The C++11 standard library is broadly thread safe. The thread safety guarantees on PRNG objects are the same as on containers. More specifically, since the PRNG classes are all pseudo-random, i.e. they generate a deterministic sequence based on a definite current state, there is really no room to be peeking or poking at anything outside … Read more
In Swift 4, func executeMultiTask() { //1. Create group let taskGroup = DispatchGroup() //2. Enter group taskGroup.enter() myTask1.execute(completeHandler: { // … //3. Leave group taskGroup.leave() //< balance with taskGroup.enter() }) /* Add more tasks … //2. Enter group taskGroup.enter() myTask2.execute(completeHandler: { //3. Leave group defer { // Use `defer` to make sure, `leave()` calls are … Read more
I need to use something like this fairly regularly within my Mac and iOS applications, so I use the following helper function (originally described in this answer): void runOnMainQueueWithoutDeadlocking(void (^block)(void)) { if ([NSThread isMainThread]) { block(); } else { dispatch_sync(dispatch_get_main_queue(), block); } } which you call via runOnMainQueueWithoutDeadlocking(^{ //Do stuff }); This is pretty much … Read more
Here’s a good example for you to try. Feel free to come back if you have any questions: self.mainThreadContext… // This is a reference to your main thread context NSPersistentStoreCoordinator *mainThreadContextStoreCoordinator = [self.mainThreadContext persistentStoreCoordinator]; dispatch_queue_t request_queue = dispatch_queue_create(“com.yourapp.DescriptionOfMethod”, NULL); dispatch_async(request_queue, ^{ // Create a new managed object context // Set its persistent store coordinator NSManagedObjectContext … Read more