grand-central-dispatch

This question already has an answer here: Prevent dispatch_after() background task from being executed 10 answers Is there a way to cancel dispatch_after() scheduled for some time in future, and haven't fired so far? I'm trying to make something like a scheduler for updates from server, and this method is just like I want, but, I'd love to cancel and re-schedule it at some point. Is it possible at all or I have to fallback and use NSTimer? There is NO way to prevent a dispatch_block from executing once it has been dispatch to it's queue, meaning that your dispatch_after cannot be canceled.

I've implemented a block that is dispatched asynchronously using GCD as follows: __block BOOL retValue; dispatch_async(dispatch_get_global_queue(0, 0), ^{ retValue = [self GCDHandler:actionName WithServiceType:serviceType :arguments]; }); return retValue; How do I cancel such a block if it is running for longer than I would like? Is there a way to cancel GCD-dispatched blocks, or provide a timeout to them? There is no built in way to cancel GCD blocks. They're rather set and forget. One way I've done this in the past is to provide 'tokens' for blocks. - (NSString*)dispatchCancelable:(dispatch

Reposting with more concise and focused question after original question went unanswered. Also adding more insight into the problem after another day of research: In my app delegate ( didFinishLaunching ), I set up a callEventHandler on CTCallCenter . The idea is that when a callState changes, I post a notification with a userInfo dict containing the call.callState . In my view, I observe this notification, and when the userInfo dict contains a value of CTCallDisconnected , I want to unhide a view. The problem I'm having is that the unhiding aspect is taking, almost consistenly, ~ 7 seconds.

I am displaying some text and images in a UITableView . The image first gets downloaded. Since before the image gets downloaded, I don't know the size of image, so I initially put a UIImageView of some fixed size. And when the image is downloaded, I resize the UIImageView . dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ // Download image dispatch_async(dispatch_get_main_queue(), ^{ // UIImageView resizing }); }); All this happens in cellForRowAtIndexPath . The issues I am facing here are : 1. How do I update the height of cell ? Considering that there can be

I am executing a block using dispatch_sync and the block is executed correctly. But this block is executed on the main thread. As per the Apple Doc: Serial queues (also known as private dispatch queues) execute one task at a time in the order in which they are added to the queue. The currently executing task runs on a distinct thread (which can vary from task to task) that is managed by the dispatch queue. which means (or what I understood) that current process that is being executed will run on a separate thread. Below is the code that I am using to judge what's going on. It is being called