I have created A Queue like this
dispatch_queue_t myBackgroundQueue;
myBackgroundQueue = dispatch_queue_create("com.google.task", NULL);
dispatch_async(myBackgroundQueue, ^(void) {
});
this will be called on button click and i would like to know the current background running queues. Thank
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
BOOL ok = // some result
// do some long running processing here
// Check that there was not a nil handler passed.
if( completionHandler )
{
// This assumes ARC. If no ARC, copy and autorelease the Block.
[completionHandler performSelector:#selector(rmaddy_callBlockWithBOOL:)
onThread:origThread
withObject:#(ok) // or [NSNumber numberWithBool:ok]
waitUntilDone:NO];
}
});
});
Related
I am creating a serial queue in which i add two task as shown below
dispatch_queue_t serial = dispatch_queue_create("com.apple.serial", DISPATCH_QUEUE_SERIAL);
**//Task 1**
dispatch_async(serial, ^{
[NMUserAPIManager getUserProfileData:^(NMUser *objUser) {
NSLog(#"Get User Profile .....");
_objUser = objUser;
}];
});
**//Task 2**
dispatch_async(serial, ^{
[NMUserAPIManager getUserRecentTransactionData:^(NSDictionary *responseDictionary) {
_accountTableView.hidden = NO;
[self recentTransactionSetup:responseDictionary];
NSLog(#"Get User Recent transaction");
dispatch_async(dispatch_get_main_queue(), ^{
[self reloadTableData];
});
}];
});
Inside that two task i am calling web service with NSURLSession. Problem is that before my Task 1 completion handle Task2 completion handle get called. According to theory by using serial queue each task waits for the previous task to finish before being executed. It my understanding is correct.
NSURLSession's already run on a background thread, so the issue you are seeing here is that as far as your serial queue is concerned once you call 'getUserProfileData:' technically the work for that block in your queue is finished because the NSURLSession is running on a different thread. If your main goal here is to simply call your second task after your first one completes I don't think you need your own queue you would probably be better off simply doing something like:
[NMUserAPIManager getUserProfileData:^(NMUser *objUser) {
NSLog(#"Get User Profile .....");
_objUser = objUser;
[self getUserTransactions];
}];
-(void)getUserTransactions
{
[NMUserAPIManager getUserRecentTransactionData:^(NSDictionary *responseDictionary) {
_accountTableView.hidden = NO;
[self recentTransactionSetup:responseDictionary];
NSLog(#"Get User Recent transaction");
dispatch_async(dispatch_get_main_queue(), ^{
[self reloadTableData];
});
}];
}
EDIT:
If you are looking for something a little more robust I would check out this post for how you can subclass NSOperation to make your own Asynchronous Operation which you can then use with an NSOperationQueue.
I have a function:
- (void)fetchClassListOnCompletion:(void(^) (BOOL success, NSArray *classlist))completionBlock;
I want to call this function from two different thread (may be simultaneously) and want the classlist from the one that finished last.
Need help to implement this
Try this:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
[self fetchClassListOnCompletion:^(BOOL success, NSArray *classlist) {
self.classList = classlist;
}];
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
[self fetchClassListOnCompletion:^(BOOL success, NSArray *classlist) {
self.classList = classlist;
}];
});
self.classList will be assigned to classlist from the block that finishes last.
Because this runs on background thread, make sure your method doesn't need to be run on main thread.
Code:
dispatch_async(
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
[ServerAPI API_GetChatList:self
withUserId:[self getUserIDFromUserDefaults]
withScheduleId:strGroupId
withType:#"group"];
dispatch_async(dispatch_get_main_queue(), ^{
[self performSelector:#selector(getChatList)
withObject:nil
afterDelay:10];
});
});
I used dispatch global queue to call a method for every 10 seconds.It is working fine.The problem is global queue is keep running in other controllers too.How do i stop this from running?any help will be appreciated.
You can keep a BOOL property,before every call, you check this property. When you want to stop, set it to YES
#property (atomic) BOOL stop;
Function
-(void)getChatList {
if (self.stop) {
return;
}
dispatch_async(
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
//Do something
dispatch_async(dispatch_get_main_queue(), ^{
if (!self.stop) {
[self performSelector:#selector(getChatList)
withObject:nil
afterDelay:10];
}
});
});
}
I am looking for a small scenario that how can we trace the "dispatch_async" is running or not?.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
(unsigned long)NULL), ^(void) {
//back ground process
});
In my case, my app will be in foreground I started the back ground thread and when I bring app from background to foreground I need to check whether it is still running or not. I should not call the same process if it is still running. any idea?
The easiest way to do this (without keeping a reference to every dispatch or a flag for entering/leaving asynchronous tasks) is by using dispatch_group notifications. See the example link and code below:
- (void)downloadPhotosWithCompletionBlock:(BatchPhotoDownloadingCompletionBlock)completionBlock
{
// 1
__block NSError *error;
dispatch_group_t downloadGroup = dispatch_group_create();
for (NSInteger i = 0; i < 3; i++) {
NSURL *url;
switch (i) {
case 0:
url = [NSURL URLWithString:kOverlyAttachedGirlfriendURLString];
break;
case 1:
url = [NSURL URLWithString:kSuccessKidURLString];
break;
case 2:
url = [NSURL URLWithString:kLotsOfFacesURLString];
break;
default:
break;
}
dispatch_group_enter(downloadGroup); // 2
Photo *photo = [[Photo alloc] initwithURL:url
withCompletionBlock:^(UIImage *image, NSError *_error) {
if (_error) {
error = _error;
}
dispatch_group_leave(downloadGroup); // 3
}];
[[PhotoManager sharedManager] addPhoto:photo];
}
dispatch_group_notify(downloadGroup, dispatch_get_main_queue(), ^{ // 4
if (completionBlock) {
completionBlock(error);
}
});
}
Note how:
dispatch_group_notify(downloadGroup, dispatch_get_main_queue(), ^{ // 4
if (completionBlock) {
completionBlock(error);
}
});
will not be called until after
dispatch_group_leave(downloadGroup); // 3
is called.
You should setup your threading to where you can work with callbacks like this to determine states. You should try to avoid using boolean flags at all costs, as this is exactly what dispatch groups are for. It's also hard to keep track of numerous asynchronous calls using boolean states.
link: dispatch groups
The question is wrong - dispatch_async is running while you call it and stops running when the call returns, which is practically immediately. What you really want to know is whether the dispatched block is running or not. The simplest way is something along the lines of
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
(unsigned long)NULL), ^(void) {
[self blockIsRunning:YES];
// do stuff
[self blockIsRunning:NO];
});
or if you want to know whether the block has run once, you would do something like
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
(unsigned long)NULL), ^(void) {
[self blockStarted];
// do stuff
[self blockFinished];
});
Alternatively, use NSOperationQueue and a subclass of NSOperation so instead of an anonymous block you have a proper object that you can ask whether it is ready, cancelled, executing, or finished.
I have a method in which I run a couple of other methods. These have completion blocks, I only want to return a value at the end of my main method once I have a result from each of my sub methods. Example:
-(NSMutableDictionary *)mainMethod
{
[self subMethod1Complete:^(NSMutableArray *results)
{
}
[self subMethod2Complete:^(NSMutableArray *results)
{
}
//return...
}
I only want to return my dictionary at the end once the two sub method have completed. How can I do this?
I did have the idea of storing a BOOL for each method, so I know, NO incomplete and YES complete. So when both are YES, I return my dict. But how I can call it on time and not prematurely?
Update
I have tweaked my code to use a completion block, so when I finally receive the data from two other completion blocks from other methods, I run the final one with compiled results. Below you can see my method. You can see my method below, no success thus far, the final completion block is still getting called prematurely.
Important bits for me. getTitles and getThumbnails methods. In the completion block of these I get the data I need. Only when I have both of these, do I want to call my final completion block of this main method. As a result, it will pass on both titles and thumbnails once they have been received.
-(void)getFeedForUserID:(NSString *)channelID delegate:(id<YTHelperDelegate>)delegate complete:(void (^)(NSMutableDictionary * result))completionBlock properties:(NSString *)element, ...
{
va_list args;
va_start(args, element);
NSMutableArray *array = [NSMutableArray new];
for (NSString *arg = element; arg != nil; arg = va_arg(args, NSString *)) [array addObject:arg];
va_end(args);
NSMutableDictionary *resultsDict = [NSMutableDictionary new];
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_group_t group = dispatch_group_create();
for (NSString *string in array)
{
if ([string isEqualToString:kFeedElementTitle])
{
dispatch_group_async(group, queue, ^{
[self getTitlesArrayForChannel:channelID completionHandler:^(NSMutableArray *results) {
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:results forKey:kFeedElementTitle];
});
}];
});
}
if ([string isEqualToString:kFeedElementTitle])
{
dispatch_group_async(group, queue, ^{
[self getThumbnailsArrayForChannel:channelID completionHandler:^(NSMutableArray *results) {
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:results forKey:kFeedElementThumbnail];
});
}];
});
}
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
completionBlock(resultsDict);
});
}
You can use GCD and the dispatch groups feature. Here's an article that explains it: http://www.objc.io/issue-2/low-level-concurrency-apis.html#groups
For example in your case, your code might look something like this (shamelessly copied from the article and adapted a bit)...
- (void)asyncMethod {
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_group_async(group, queue, ^(){
NSMutableArray * results = [self subMethod1];
dispatch_group_async(group, dispatch_get_main_queue(), ^(){
self.subMethod1Results = results;
});
});
dispatch_group_async(group, queue, ^(){
NSMutableArray * results = [self subMethod2];
dispatch_group_async(group, dispatch_get_main_queue(), ^(){
self.subMethod2Results = results;
});
});
// This block will run once everything above is done:
dispatch_group_notify(group, dispatch_get_main_queue(), ^(){
// notify the app that both sets of data are ready
[self notifyWorkIsDone];
// and release the dispatch group
dispatch_release(group);
});
}
This requires a little modification to how your class works, because the above method is asynchronous (which is a good thing--it's not going to block your app while all that work is being done). All you need is some sort of handler to call and notify your app that your data is ready and you can update your UI or do whatever additional processing is necessary.
You are looking for GCD's dispatch_group APIs. Here is some sample code from Apple's Concurrency Programming Guide:
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
// Add a task to the group
dispatch_group_async(group, queue, ^{
// Some asynchronous work
});
// Do some other work while the tasks execute.
// When you cannot make any more forward progress,
// wait on the group to block the current thread.
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
// Release the group when it is no longer needed.
dispatch_release(group);
Comments on updated code:
Are you sure your mistake is not that your second if statement checks kFeedElementTitle a second time instead of kFeedElementThumbnail which I think may be what you intended?
Updated with working example:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
NSString *kFeedElementTitle = #"some";
NSString *kFeedElementThumbnail = #"strings";
NSArray *array = #[#"some", #"test", #"strings"];
NSMutableDictionary *resultsDict = [NSMutableDictionary new];
NSLog(#"App launched");
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
for (NSString *string in array)
{
if ([string isEqualToString:kFeedElementTitle])
{
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:5]; // simulate network call
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:#"title result" forKey:kFeedElementTitle];
NSLog(#"Received title result");
});
});
}
if ([string isEqualToString:kFeedElementThumbnail]) // Note: this was changed to kFeedElementThumbnail from kFeedElementTitle
{
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:10]; // simulate network call
dispatch_group_async(group, dispatch_get_main_queue(), ^{
[resultsDict setObject:#"thumbnail result" forKey:kFeedElementThumbnail];
NSLog(#"Received thumbnail result");
});
});
}
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(#"final dictionary: %#", resultsDict);
});
return YES;
}
Output:
2013-07-16 21:02:46.468 d[947:a0b] App launched
2013-07-16 21:02:51.471 d[947:a0b] Received title result
2013-07-16 21:02:56.471 d[947:a0b] Received thumbnail result
2013-07-16 21:02:56.472 d[947:a0b] final dictionary: {
some = "title result";
strings = "thumbnail result";
}
you do not know when the blocks are going to return so you will not know if you have the data at the time, if i may make a suggestion you call a method with in those blocks that method will check to see if both dictionaries are set and if they are then continue with the process otherwise don't continue
- (void)mainMethod
{
[self subMethod1Complete:^(NSMutableArray *results)
{
self.result1 = results;
[self method3];
}
[self subMethod2Complete:^(NSMutableArray *results)
{
self.results2 = results;
[self method3];
}
}
- (void)method3 {
if ( self.results1 != nil && self.results2 != nil ) {
[self startProcedure];
} else {
// do nothing
}
}
although all together i would suggest reworking your code to do this differently, simply because you can't guarantee that one of the blocks will be done by the time of the return, let alone both of them
you can also do something like this
-(NSMutableDictionary *)mainMethod
{
[self subMethod1Complete:^(NSMutableArray *results)
{
}
[self subMethod2Complete:^(NSMutableArray *results)
{
}
while(result == nil)
sleep(1);
//return...
}
which again is really bad.... it's just better to re-write the code