Remove async calls from SDWebImageDownloader. The operation is already run in a background thread also the async calls are unnecessary.

SDWebImage/SDWebImageDownloader.m

@@ -23,7 +23,6 @@ static NSString *const kCompletedCallbackKey = @"completed";
 @property (strong, nonatomic) NSMutableDictionary *URLCallbacks;
 @property (strong, nonatomic) NSMutableDictionary *HTTPHeaders;
 // This queue is used to serialize the handling of the network responses of all the download operation in a single queue
-@property (SDDispatchQueueSetterSementics, nonatomic) dispatch_queue_t workingQueue;
 @property (SDDispatchQueueSetterSementics, nonatomic) dispatch_queue_t barrierQueue;
 
 @end
@@ -72,7 +71,6 @@ static NSString *const kCompletedCallbackKey = @"completed";
         _downloadQueue.maxConcurrentOperationCount = 2;
         _URLCallbacks = NSMutableDictionary.new;
         _HTTPHeaders = [NSMutableDictionary dictionaryWithObject:@"image/*" forKey:@"Accept"];
-        _workingQueue = dispatch_queue_create("com.hackemist.SDWebImageDownloader", DISPATCH_QUEUE_SERIAL);
         _barrierQueue = dispatch_queue_create("com.hackemist.SDWebImageDownloaderBarrierQueue", DISPATCH_QUEUE_CONCURRENT);
     }
     return self;
@@ -81,7 +79,6 @@ static NSString *const kCompletedCallbackKey = @"completed";
 - (void)dealloc
 {
     [self.downloadQueue cancelAllOperations];
-    SDDispatchQueueRelease(_workingQueue);
     SDDispatchQueueRelease(_barrierQueue);
 }
 
@@ -124,7 +121,7 @@ static NSString *const kCompletedCallbackKey = @"completed";
         request.HTTPShouldHandleCookies = NO;
         request.HTTPShouldUsePipelining = YES;
         request.allHTTPHeaderFields = wself.HTTPHeaders;
-        operation = [SDWebImageDownloaderOperation.alloc initWithRequest:request queue:wself.workingQueue options:options progress:^(NSUInteger receivedSize, long long expectedSize)
+        operation = [SDWebImageDownloaderOperation.alloc initWithRequest:request options:options progress:^(NSUInteger receivedSize, long long expectedSize)
         {
             if (!wself) return;
             SDWebImageDownloader *sself = wself;

SDWebImage/SDWebImageDownloaderOperation.h

@@ -16,7 +16,6 @@
 @property (assign, nonatomic, readonly) SDWebImageDownloaderOptions options;
 
 - (id)initWithRequest:(NSURLRequest *)request
-                queue:(dispatch_queue_t)queue
               options:(SDWebImageDownloaderOptions)options
              progress:(SDWebImageDownloaderProgressBlock)progressBlock
             completed:(SDWebImageDownloaderCompletedBlock)completedBlock

SDWebImage/SDWebImageDownloaderOperation.m

@@ -21,7 +21,6 @@
 @property (assign, nonatomic) long long expectedSize;
 @property (strong, nonatomic) NSMutableData *imageData;
 @property (strong, nonatomic) NSURLConnection *connection;
-@property (SDDispatchQueueSetterSementics, nonatomic) dispatch_queue_t queue;
 
 @end
 
@@ -31,11 +30,10 @@
     BOOL responseFromCached;
 }
 
-- (id)initWithRequest:(NSURLRequest *)request queue:(dispatch_queue_t)queue options:(SDWebImageDownloaderOptions)options progress:(void (^)(NSUInteger, long long))progressBlock completed:(void (^)(UIImage *, NSData *, NSError *, BOOL))completedBlock cancelled:(void (^)())cancelBlock
+- (id)initWithRequest:(NSURLRequest *)request options:(SDWebImageDownloaderOptions)options progress:(void (^)(NSUInteger, long long))progressBlock completed:(void (^)(UIImage *, NSData *, NSError *, BOOL))completedBlock cancelled:(void (^)())cancelBlock
 {
     if ((self = [super init]))
     {
-        _queue = queue;
         _request = request;
         _options = options;
         _progressBlock = [progressBlock copy];
@@ -51,8 +49,6 @@
 
 - (void)start
 {
-    dispatch_async(dispatch_get_main_queue(), ^
-    {
     if (self.isCancelled)
     {
         self.finished = YES;
@@ -63,12 +59,6 @@
     self.executing = YES;
     self.connection = [NSURLConnection.alloc initWithRequest:self.request delegate:self startImmediately:NO];
 
-        // If not in low priority mode, ensure we aren't blocked by UI manipulations (default runloop mode for NSURLConnection is NSEventTrackingRunLoopMode)
-        if (!(self.options & SDWebImageDownloaderLowPriority))
-        {
-            [self.connection scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
-        }
-
     [self.connection start];
 
     if (self.connection)
@@ -78,6 +68,9 @@
             self.progressBlock(0, -1);
         }
         [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStartNotification object:self];
+
+        // Make sure to run the runloop in our background thread so it can process downloaded data
+        CFRunLoopRun();
     }
     else
     {
@@ -86,7 +79,6 @@
             self.completedBlock(nil, nil, [NSError errorWithDomain:NSURLErrorDomain code:0 userInfo:@{NSLocalizedDescriptionKey: @"Connection can't be initialized"}], YES);
         }
     }
-    });
 }
 
 - (void)cancel
@@ -118,14 +110,11 @@
 
 - (void)reset
 {
-    dispatch_async(dispatch_get_main_queue(), ^
-    {
     self.cancelBlock = nil;
     self.completedBlock = nil;
     self.progressBlock = nil;
     self.connection = nil;
     self.imageData = nil;
-    });
 }
 
 - (void)setFinished:(BOOL)finished
@@ -182,8 +171,6 @@
     [self.imageData appendData:data];
 
     if ((self.options & SDWebImageDownloaderProgressiveDownload) && self.expectedSize > 0 && self.completedBlock)
-    {
-        dispatch_async(self.queue, ^
     {
         // The following code is from http://www.cocoaintheshell.com/2011/05/progressive-images-download-imageio/
         // Thanks to the author @Nyx0uf
@@ -251,21 +238,19 @@
         }
 
         CFRelease(imageSource);
-        });
         
         NSUInteger received = self.imageData.length;
-        dispatch_async(dispatch_get_main_queue(), ^
+
-        {
         if (self.progressBlock)
         {
             self.progressBlock(received, self.expectedSize);
         }
-        });
     }
 }
 
 - (void)connectionDidFinishLoading:(NSURLConnection *)aConnection
 {
+    CFRunLoopStop(CFRunLoopGetCurrent());
     self.connection = nil;
 
     [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
@@ -281,12 +266,8 @@
             [self done];
         }
         else
-        {
-            dispatch_async(self.queue, ^
         {
             UIImage *image = [UIImage decodedImageWithImage:SDScaledImageForPath(self.request.URL.absoluteString, self.imageData)];
-                dispatch_async(dispatch_get_main_queue(), ^
-                {
             if (CGSizeEqualToSize(image.size, CGSizeZero))
             {
                 completionBlock(nil, nil, [NSError errorWithDomain:@"SDWebImageErrorDomain" code:0 userInfo:@{NSLocalizedDescriptionKey: @"Downloaded image has 0 pixels"}], YES);
@@ -297,8 +278,6 @@
             }
             self.completionBlock = nil;
             [self done];
-                });
-            });
         }
     }
     else
@@ -309,6 +288,7 @@
 
 - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
 {
+    CFRunLoopStop(CFRunLoopGetCurrent());
     [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
 
     if (self.completedBlock)