Canceling the SDWebImageOperation will also cancel the expensive disk cache query operation.

SDWebImage/SDImageCache.h

@@ -98,7 +98,7 @@ typedef enum SDImageCacheType SDImageCacheType;
  *
  * @param key The unique key used to store the wanted image
  */
-- (void)queryDiskCacheForKey:(NSString *)key done:(void (^)(UIImage *image, SDImageCacheType cacheType))doneBlock;
+- (NSOperation *)queryDiskCacheForKey:(NSString *)key done:(void (^)(UIImage *image, SDImageCacheType cacheType))doneBlock;
 
 /**
  * Query the memory cache synchronously.

SDWebImage/SDImageCache.m

@@ -251,14 +251,16 @@ static const NSInteger kDefaultCacheMaxCacheAge = 60 * 60 * 24 * 7; // 1 week
     return SDScaledImageForKey(key, image);
 }
 
-- (void)queryDiskCacheForKey:(NSString *)key done:(void (^)(UIImage *image, SDImageCacheType cacheType))doneBlock
+- (NSOperation *)queryDiskCacheForKey:(NSString *)key done:(void (^)(UIImage *image, SDImageCacheType cacheType))doneBlock
 {
-    if (!doneBlock) return;
+    NSOperation *operation = NSOperation.new;
+    
+    if (!doneBlock) return nil;
 
     if (!key)
     {
         doneBlock(nil, SDImageCacheTypeNone);
-        return;
+        return nil;
     }
 
     // First check the in-memory cache...
@@ -266,11 +268,16 @@ static const NSInteger kDefaultCacheMaxCacheAge = 60 * 60 * 24 * 7; // 1 week
     if (image)
     {
         doneBlock(image, SDImageCacheTypeMemory);
-        return;
+        return nil;
     }
 
     dispatch_async(self.ioQueue, ^
     {
+        if (operation.isCancelled)
+        {
+            return;
+        }
+        
         @autoreleasepool
         {
             UIImage *diskImage = [self diskImageForKey:key];
@@ -286,6 +293,8 @@ static const NSInteger kDefaultCacheMaxCacheAge = 60 * 60 * 24 * 7; // 1 week
             });
         }
     });
+    
+    return operation;
 }
 
 - (void)removeImageForKey:(NSString *)key

SDWebImage/SDWebImageManager.m

@@ -14,6 +14,7 @@
 
 @property (assign, nonatomic, getter = isCancelled) BOOL cancelled;
 @property (copy, nonatomic) void (^cancelBlock)();
+@property (strong, nonatomic) NSOperation *cacheOperation;
 
 @end
 
@@ -108,9 +109,17 @@
     }
     NSString *key = [self cacheKeyForURL:url];
 
-    [self.imageCache queryDiskCacheForKey:key done:^(UIImage *image, SDImageCacheType cacheType)
+    operation.cacheOperation = [self.imageCache queryDiskCacheForKey:key done:^(UIImage *image, SDImageCacheType cacheType)
     {
-        if (operation.isCancelled) return;
+        if (operation.isCancelled)
+        {
+            @synchronized(self.runningOperations)
+            {
+                [self.runningOperations removeObject:operation];
+            }
+
+            return;
+        }
 
         if ((!image || options & SDWebImageRefreshCached) && (![self.delegate respondsToSelector:@selector(imageManager:shouldDownloadImageForURL:)] || [self.delegate imageManager:self shouldDownloadImageForURL:url]))
         {
@@ -138,7 +147,7 @@
             }
             id<SDWebImageOperation> subOperation = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *data, NSError *error, BOOL finished)
             {                
-                if (weakOperation.cancelled)
+                if (weakOperation.isCancelled)
                 {
                     dispatch_main_sync_safe(^
                     {
@@ -272,6 +281,11 @@
 - (void)cancel
 {
     self.cancelled = YES;
+    if (self.cacheOperation)
+    {
+        [self.cacheOperation cancel];
+        self.cacheOperation = nil;
+    }
     if (self.cancelBlock)
     {
         self.cancelBlock();