grand-central-dispatch

问题 I try to understand GCD and wrote this code to find out run priority: override func viewDidLoad() { super.viewDidLoad() fetchImage() print(1) dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0)) { print(2) } dispatch_async(dispatch_get_main_queue()) { print(3) } dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INTERACTIVE, 0)) { print(5) } } I got next result in the console: 1 2 5 3 So the question is: Part 1 : Why 3 is after 5 (main_queue has highest priority?) Part

问题 I've been having problems with my multi-threaded Core Data enabled app, and I figured I should take a hard look at what I'm doing and how. Please let me know if the following should work. I have a singleton DataManager class that handles the Core Data stuff. It has a property managedObjectContext that returns a different MOC for each thread. So, given NSMutableDictionary *_threadContextDict (string thread names to contexts) and NSMutableDictionary *_threadDict (string thread names to threads)

问题 I am working on a feed reader and i am doing it by parsing rss feeds using nsxmlparser. I also have thumbnail objects that i am taking from the CDATA block. -(void)parser:(NSXMLParser *)parser foundCDATA:(NSData *)CDATABlock { dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ NSString *someString = [[NSString alloc] initWithData:CDATABlock encoding:NSUTF8StringEncoding]; NSString *storyImageURL = [self getFirstImageUrl:someString]; NSURL *tempURL = [NSURL

问题 dispatch_once call causes crash (in simulator) after I've converted my project to ARC. My original problem was that I've got EXC_BAD_ACCESS (in objc_retain call) crash in one of my singleton object's + (SingletonClass)shared { ... dispatch_once(..., ^{}); ... } method exactly one line before the dispatch_once call. Based on loggings, and breakpoints my code have not run into the dispatch_once call's block. I didn't know the reason, so I've just commented out the dispatch_once call. My app

问题 What I am trying to do I am using the code below to download data (historic foreign exchange rates) from my backend server (parse.com) to my app's Core Data store. The app checks for the latest available data stored locally and fetches only the newer data from the server. If there is no data stored locally yet, it fetches all data from the server. The way the code is set up, it fetches the data in batches of 100 objects, saves the objects in Core Data, gets the new latest date for which data

问题 If I create a singleton inside of +[NSObject initialize] , do I need to put my code inside a dispatch_once block like so? static NSObject * Bar; @implementation Foo + (void)initialize { if (self == [Foo class]) { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ Bar = [NSObject new]; }); } } @end EDIT I'm concerned about this because I want to make sure that all threads will see that I've set Bar after +[Foo initialize] is called. The documentation says +[NSObject initialize] is

问题 Im doing some lengthy calculations to create chart data on a background thread i was originally use GCD, but every time a user filters the chart data by hitting a button, the chart data needs to be recalculated, if the user clicks the chart data filtering buttons very quickly (power user) then the chart loops through each drawing as each GCD dispatch async finishes I realize that I can't cancel threads with GCD so I've moved to trying to implement an OperationQueue I call cancelAllOperations(

问题 I'm using Grand Central Dispatch to load images of a UITableViewCell asynchronously. This works well except in some border cases in which the cell is reused, and a previous block loads the wrong image. My current code looks like this: - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (!cell) { cell = [[

问题 I've found an issue that seems to be causing a deadlock in WebKit. If I run this code from my main thread, I rightly see an alert. I can tap on the "OK" button on the alert and it dismisses and all is working well: [theWebView stringByEvaluatingJavaScriptFromString:@"alert('hi');"]; If I make a slight modification, then the alert message still appears, but the OK button cannot be tapped on - you cannot dismiss the alert and if you break into the app it is hung in the

问题 This question already has answers here : Swift 3.0 unresolved identifier for DispatchQueue (2 answers) Closed 3 years ago . I am trying to take/record video asynchronously on the main thread. However, when I call dispatch.main.async , I always get the error: use of unresolved identifier DispatchQueue I've looked everywhere from WWDC to Apple's Documentation, but I see no evidence of the type being deprecated. Here is the code: if !self.cameraEngine.isRecording { if let url =