Background thread completion blocks possibly firing before completion - ios

Question

I am writing a photo upload queue manager.
Here is my process. The user can take a picture or choose one from the camera roll.
The image, along with some other string data, is placed in queue.
The queue is simply an array that contains the image path string and the other string data. The 'queued' image is saved to the documents directory of the application for later retrieval.
Every second the queue is checked to see if any images that need to be uploaded, then it does so, one-by-one.
When it uploads, the server responds with a string of success, if success then the picture is removed from list queue, the temp image is deleted and the program moves on to the next queued image.
If I call the uploadImage: method independently and pass it the image and string data, the image uploads fine. But when called from a background thread, the image is never truly uploaded even though the server responds success instantly. I feel like since the server is responding instantly with success, that the image is only partially being uploaded.
processImage: is the method that calls uploadImage: from the background.
I could really use an expert's eyes to see what might be causing the app to not fully wait on the photo to upload before continuing.
#interface ImageUploader ()
#property (nonatomic, strong) NSMutableArray * arrPhotoQueue;
#property (nonatomic, strong) NSTimer* timerUpload;
#end
#implementation ImageUploader {
NSUserDefaults * defaults; //Just were we are currently storing a list of images.
NSArray *paths;
NSString *documentsDirectory;
}
#pragma mark Public Methods
- (void) startPhotoUploadCheck {
if (!_timerUpload) {
if(![_timerUpload isValid]){
_timerUpload = [NSTimer scheduledTimerWithTimeInterval:_timerCheckInterval target:self selector:#selector(checkForPhotosToUpload) userInfo:nil repeats:YES];
}
}
}
- (void) addImageToQueue:(UIImage*)image withCallKey:(NSString*) callKey {
NSData *imageData = UIImagePNGRepresentation(image);
NSString *fileName = [NSString stringWithFormat:#"%#.png",[self randomStringWithLength:8]];
NSString *imagePath =[documentsDirectory stringByAppendingPathComponent:fileName];
NSMutableDictionary * data = [[NSMutableDictionary alloc] init];
[data setValue:fileName forKey:#"imagePath"];
[data setValue:callKey forKey:#"callKey"];
[_arrPhotoQueue addObject:data];
if (![imageData writeToFile:imagePath atomically:NO]) {
NSLog(#"Failed to cache image data to disk");
} else {
NSLog(#"Image %#", fileName);
[defaults setObject:_arrPhotoQueue forKey:#"PendingPhotos"];
[defaults synchronize];
}
[self totalImagesInQueue];
}
- (void) checkForPhotosToUpload {
//this does some logic to just see if there is a connection to the internet and that there are photos in queue then it calls
[self proceedWithUpload];
}
#pragma mark Upload Image
- (int) removePhotoFromMemory:(NSString *) callKeyOfUploadedPhoto
{
int nIndexOfUploadedPhoto = -1;
for (int i = 0; i < [_arrPhotoQueue count]; i++) {
NSString * callKey = [_arrPhotoQueue[i] objectForKey:#"callKey"];
if ([callKey isEqualToString:callKeyOfUploadedPhoto]) {
//remove uploaded photo
NSString *imagePath = [documentsDirectory stringByAppendingPathComponent:[_arrPhotoQueue[i] objectForKey:#"imagePath"]];
NSLog(#"Remove image from queue: %#", [_arrPhotoQueue[i] objectForKey:#"imagePath"]);
[[NSFileManager defaultManager] removeItemAtPath:imagePath error:nil];
nIndexOfUploadedPhoto = i;
break;
}
}
return nIndexOfUploadedPhoto;
}
- (void) proceedWithUpload {
NSMutableArray* removeArray = [[NSMutableArray alloc] init];
dispatch_group_t taskGroup = dispatch_group_create();
for (int i = 0; i < [_arrPhotoQueue count]; i++) {
dispatch_group_enter(taskGroup);
UIImage * image = [UIImage imageWithContentsOfFile:[_arrPhotoQueue[i] objectForKey:#"imagePath"]];
NSString * callKey = [_arrPhotoQueue[i] objectForKey:#"callKey"];
[self processImage:image :callKey completed:^(bool bSuccess){
if (bSuccess) {
//photo is uploaded successfully
int nPhotoIdx = [self removePhotoFromMemory:callKey];
if (nPhotoIdx > -1) {
[removeArray addObject:[NSString stringWithFormat:#"%d", nPhotoIdx]];
}
dispatch_group_leave(taskGroup);
} else {
dispatch_group_leave(taskGroup);
}
}];
}
// Here we wait for all the requests to finish
dispatch_group_notify(taskGroup, dispatch_get_main_queue(), ^{
// run code when all files are downloaded
[self removePhotoFromQueue:removeArray];
});
}
- (void) removePhotoFromQueue:(NSMutableArray*)index {
NSArray *sortedIndex = [index sortedArrayUsingComparator:^(id obj1, id obj2){
if ([obj1 isKindOfClass:[NSString class]] && [obj2 isKindOfClass:[NSString class]]) {
int nFirstIndex = (int)[obj1 integerValue];
int nSecondIndex = (int)[obj2 integerValue];
if (nFirstIndex > nSecondIndex) {
return (NSComparisonResult)NSOrderedAscending;
} else if (nFirstIndex < nSecondIndex) {
return (NSComparisonResult)NSOrderedDescending;
}
}
return (NSComparisonResult)NSOrderedSame;
}];
for (int i =0; i < [sortedIndex count]; i++) {
int nIdx = (int)[sortedIndex[i] integerValue];
[_arrPhotoQueue removeObjectAtIndex:nIdx];
}
[defaults removeObjectForKey:#"PendingPhotos"];
[defaults setObject:_arrPhotoQueue forKey:#"PendingPhotos"];
[defaults synchronize];
}
#pragma mark Image Processor
- (void) processImage:(UIImage*)image :(NSString*)callKey completed:(void(^)(bool bSuccess)) block{
__block NSMutableDictionary * message;
dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
message = [self uploadImage:image CallKey:callKey];
[self uploadImage:image CallKey:callKey];
dispatch_async(dispatch_get_main_queue(), ^{
if ([[message objectForKey:#"status"] isEqualToString:#"success"]) {
block(true);
} else {
NSLog(#"Somethign is wrong");
block(false);
}
});
});
}
- (NSMutableDictionary*) uploadImage:(UIImage *)theimage CallKey:(NSString*)callKey {
NSData * imageData = UIImageJPEGRepresentation([self fixrotation:theimage], 90);
NSString * jsonString= [JSONCommunicator buildJSONForImageUpload:[self prepareDictionaryDataForUploadWithKey:callKey]];
NSURL * uploadURL = [NSURL URLWithString:MYURL];
// create the URL
NSMutableURLRequest *postRequest = [NSMutableURLRequest requestWithURL:uploadURL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:20.0];
[postRequest setHTTPMethod:#"POST"];
// just some random text that will never occur in the body
NSString *boundary = #"---------------------------14737809831466499882746641449";
NSString *headerBoundary = [NSString stringWithFormat:#"multipart/form-data; boundary=%#", boundary];
[postRequest addValue:headerBoundary forHTTPHeaderField:#"Content-Type"];
// create data
NSMutableData *postBody = [NSMutableData data];
// JSON part
[postBody appendData:[[NSString stringWithFormat:#"--%#\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:[#"Content-Disposition: form-data; name=\"params\"\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:[jsonString dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:[#"\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
// media part
[postBody appendData:[[NSString stringWithFormat:#"--%#\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:[[NSString stringWithFormat:#"Content-Disposition: form-data; name=\"UploadedFile\"; filename=\"image.jpg\"\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:[#"Content-Type: image/jpeg\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:imageData];
[postBody appendData:[[NSString stringWithFormat:#"\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
// final boundary
[postBody appendData:[[NSString stringWithFormat:#"--%#--\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
NSString *s = [[NSString alloc] initWithData:postBody encoding:NSASCIIStringEncoding];
//NSLog(#"Image String: %#", s);
// add body to post
[postRequest setHTTPBody:postBody];
// pointers to some necessary objects
NSURLResponse* response;
NSError* error;
// synchronous filling of data from HTTP POST response
NSData *responseData = [NSURLConnection sendSynchronousRequest:postRequest returningResponse:&response error:&error];
if (error) {
NSLog(#"Error: %#", [error localizedDescription]);
}
// convert data into string
NSString *responseString = [[NSString alloc] initWithBytes:[responseData bytes] length:[responseData length] encoding:NSUTF8StringEncoding];
NSLog(#"TOPS Response String: %#", responseString);
NSData *data = [responseString dataUsingEncoding:NSUTF8StringEncoding];
NSMutableDictionary * dictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
return dictionary;
}