Fix NSNotificationCenter dispatch on subthreads.

Author: Naoki Morita

SDWebImage/SDWebImageDownloaderOperation.m

@@ -95,7 +95,9 @@ - (void)start {
         if (self.progressBlock) {
             self.progressBlock(0, NSURLResponseUnknownLength);
         }
-        [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStartNotification object:self];
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStartNotification object:self];
+        });
 
         if (floor(NSFoundationVersionNumber) <= NSFoundationVersionNumber_iOS_5_1) {
             // Make sure to run the runloop in our background thread so it can process downloaded data
@@ -150,7 +152,9 @@ - (void)cancelInternal {
 
     if (self.connection) {
         [self.connection cancel];
-        [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:self];
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:self];
+        });
 
         // As we cancelled the connection, its callback won't be called and thus won't
         // maintain the isFinished and isExecuting flags.
@@ -216,8 +220,9 @@ - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLRespon
         } else {
             [self.connection cancel];
         }
-        
-        [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
+        });
 
         if (self.completedBlock) {
             self.completedBlock(nil, nil, [NSError errorWithDomain:NSURLErrorDomain code:[((NSHTTPURLResponse *)response) statusCode] userInfo:nil], YES);
@@ -340,7 +345,9 @@ - (void)connectionDidFinishLoading:(NSURLConnection *)aConnection {
         CFRunLoopStop(CFRunLoopGetCurrent());
         self.thread = nil;
         self.connection = nil;
-        [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
+        });
     }
 
     if (![[NSURLCache sharedURLCache] cachedResponseForRequest:_request]) {
@@ -377,7 +384,9 @@ - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)err
         CFRunLoopStop(CFRunLoopGetCurrent());
         self.thread = nil;
         self.connection = nil;
-        [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
+        });
     }
 
     if (self.completedBlock) {