grand-central-dispatch

I have those methods to retrieve some object information from the internet: - (void)downloadAppInfo:(void(^)())success failure:(void(^)(NSError *error))failure; - (void)getAvailableHosts:(void(^)())success failure:(void(^)(NSError *error))failure; - (void)getAvailableServices:(void(^)())success failure:(void(^)(NSError *error))failure; - (void)getAvailableActions:(void(^)())success failure:(void(^)(NSError *error))failure; The downloaded stuff gets stored in object properties, so that is why the success functions return nothing. Now, I want to have one method like this: - (void)syncEverything:

It may be a dumb question but I need to ask and clear this up for myself. To submit a block onto a queue for execution, use the functions dispatch_sync and dispatch_async . They both take a queue and a block as parameters. dispatch_async returns immediately, running the block asynchronously, while dispatch_sync blocks execution until the provided block returns. Here are some situations: Situation 1 dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul); dispatch_async(queue, ^{ [self goDoSomethingLongAndInvolved]; dispatch_async(queue, ^{ NSLog(@"this is

I am reading Concurrency Programming Guide and things confuse me. I see a lot of code invoking the following for any background task: dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); Now what I mean by 'background' is the popular meaning: Something that gets executed anywhere other than the main (UI) thread So following the docs, the above statement returns any non-main-thread queue with differing priorities. My question is - why does then DISPATCH_QUEUE_PRIORITY_BACKGROUND exist? Lately I also see many async tasks using DISPATCH_QUEUE_PRIORITY_BACKGROUND specifically to perform

I would assume that I am aware of how to work with DispatchGroup , for understanding the issue, I've tried: class ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() performUsingGroup() } func performUsingGroup() { let dq1 = DispatchQueue.global(qos: .userInitiated) let dq2 = DispatchQueue.global(qos: .userInitiated) let group = DispatchGroup() group.enter() dq1.async { for i in 1...3 { print("\(#function) DispatchQueue 1: \(i)") } group.leave() } group.wait() dq2.async { for i in 1...3 { print("\(#function) DispatchQueue 2: \(i)") } } group.notify(queue:

What I'm trying todo in a nutshell is I am using a background queue to save JSON objects pulled from a web service to the Core Data Sqlite3 database. The saving takes place on a serialized background queue I've created via GCD, and saved to a secondary instance of NSManagedObjectContext that is created for that background queue. Once the save is complete I need to update the instance of NSManagedObjectContext that is on the main thread with the newly created/updated objects. The problem I am having though is the instance of NSManagedObjectContext on the main thread is not able to find the

What's the best way of multithreading in iOS as we have three options GCD, NSThread , and NSOperationQueue ? I am confused in which one is the best? If none, then which should be used in what scenario and how they differ and also, if someone has some good example of using NSOperationQueue , please share so that I can learn. Simple answer: Use NSThread (or even the pthreads API) when you want or need to have direct control over the threads you create, e.g. you need fine-grained control over thread priorities or are interfacing with some other subsystem that vends/consumes thread objects

The following things are what I know & understand: Global queue is a concurrent queue which can dispatch tasks to multiple threads. The order of executing task is not guaranteed. e.g.: dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), { for (int i; i<10; i++) { doTask() } }) If I want to dispatch to serial queue, I can use dispatch_async(dispatch_queue_create("my.serial.queue", nil) { ... } each time only one task is dispatched to a thread & get executed. The order is FIFO. ===== What I am confused & not fully understand ======= The main thread has a NSRunLoop,

As you may remember, I am trying to use GCD to speed up some of my code, namely a collision detection and resolution engine. However, I am clearly doing something wrong because all of my GCD code is significantly slower and less consistent than my serial code (between 1.4x and 10x slower). Allow me to give you an example: I am iterating over an array in a bubble-sort fashion to determine all possible collisions among objects in that array: - (double) detectCollisionsInArray:(NSArray*)objects { int count = [objects count]; if (count > 0) { double time = CFAbsoluteTimeGetCurrent(); for (int i =