NSOperationOperationQueue cancelAllOperations method won't stop operations - ios

Question

How to cancel all operations in NSOperationQueue? I used cancelAllOperations method, but it didn't work, the NSOperationQueue is still calling server to upload photo.
I put every single connection on NSOperationQueue with loop.
- (void)sendingImage:(NSArray *)imgArray compression:(CGFloat)compression
{
hud = [MBProgressHUD showHUDAddedTo: self.view animated: YES];
hud.label.text = [NSString stringWithFormat: #"Waiting for Loading"];
[hud.button setTitle: #"Cancel" forState: UIControlStateNormal];
[hud.button addTarget: self action: #selector(cancelWork:) forControlEvents: UIControlEventTouchUpInside];
__block int photoFinished = 0;
self.queue = [[NSOperationQueue alloc] init];
self.queue.maxConcurrentOperationCount = 5;
[self.queue addObserver: self forKeyPath: #"operations" options: 0 context: NULL];
NSBlockOperation *operation = [[NSBlockOperation alloc] init];
__weak NSBlockOperation *weakOperation = operation;
__block NSString *response = #"";
for (int i = 0; i < imgArray.count; i++) {
operation = [NSBlockOperation blockOperationWithBlock:^{
[self uploadingPhoto];
}];
[operation setCompletionBlock:^{
NSLog(#"Operation 1-%d Completed", i);
photoFinished++;
dispatch_async(dispatch_get_main_queue(), ^{
hud.label.text = [NSString stringWithFormat: #"%d photo complete uploading", photoFinished];
});
}];
[self.queue addOperation: operation];
}
}
I want to press cancel button on MBProgressHUD to first canceled all the NSURLSessionDataTask and then cancel all operations, but didn't work.
- (void)cancelWork:(id)sender {
NSLog(#"cancelWork");
NSLog(#"self.queue.operationCount: %lu", (unsigned long)self.queue.operationCount);
[session getTasksWithCompletionHandler:^(NSArray<NSURLSessionDataTask *> * _Nonnull dataTasks, NSArray<NSURLSessionUploadTask *> * _Nonnull uploadTasks, NSArray<NSURLSessionDownloadTask *> * _Nonnull downloadTasks) {
if (!dataTasks || !dataTasks.count) {
return;
}
for (NSURLSessionDataTask *task in dataTasks) {
[task cancel];
if ([self.queue operationCount] > 0) {
[self.queue cancelAllOperations];
}
}
}];
}
I used semaphore to let NSURLSession become Synchronous connection.
- (void)uploadingPhoto {
request setting above
NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
config.timeoutIntervalForRequest = 1200;
session = [NSURLSession sessionWithConfiguration: config];
dataTask = [session dataTaskWithRequest: request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (error == nil) {
str = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding];
NSLog(#"str: %#", str);
}
dispatch_semaphore_signal(semaphore);
}];
NSLog(#"task resume");
[dataTask resume];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
return str;
}
Any comments or solutions will be greatly appreciated.

Answer 1

An NSOperation does not by default have support for cancellation. See the class documentation. One extract is:
Canceling an operation does not immediately force it to stop what it is doing. Although respecting the value in the cancelled property is expected of all operations, your code must explicitly check the value in this property and abort as needed.
It also seems hard to implement cancellation using NSBlockOperation.