Added the new Async API for disk data query, to avoid user to dispatch their own global queu (not IO queue), solve the IO safe issue

SDWebImage/Core/SDImageCache.h

@@ -235,6 +235,15 @@ typedef NS_OPTIONS(NSUInteger, SDImageCacheOptions) {
  */
 - (nullable NSData *)diskImageDataForKey:(nullable NSString *)key;
 
+/**
+ * Asynchronously load the image data in disk cache. You can decode the image data to image after loaded.
+ *
+ *  @param key The unique key used to store the wanted image
+ *  @param completionBlock the block to be executed when the check is done.
+ *  @note the completion block will be always executed on the main queue
+ */
+- (void)diskImageDataQueryForKey:(nullable NSString *)key completion:(nullable SDImageCacheQueryDataCompletionBlock)completionBlock;
+
 /**
  * Operation that queries the cache asynchronously and call the completion when done.
  *

SDWebImage/Core/SDImageCache.m

@@ -314,6 +314,17 @@
     return [self.diskCache containsDataForKey:key];
 }
 
+- (void)diskImageDataQueryForKey:(NSString *)key completion:(SDImageCacheQueryDataCompletionBlock)completionBlock {
+    dispatch_async(self.ioQueue, ^{
+        NSData *imageData = [self diskImageDataBySearchingAllPathsForKey:key];
+        if (completionBlock) {
+            dispatch_async(dispatch_get_main_queue(), ^{
+                completionBlock(imageData);
+            });
+        }
+    });
+}
+
 - (nullable NSData *)diskImageDataForKey:(nullable NSString *)key {
     if (!key) {
         return nil;

SDWebImage/Core/SDImageCacheDefine.h

@@ -36,6 +36,7 @@ typedef NS_ENUM(NSInteger, SDImageCacheType) {
 };
 
 typedef void(^SDImageCacheCheckCompletionBlock)(BOOL isInCache);
+typedef void(^SDImageCacheQueryDataCompletionBlock)(NSData * _Nullable data);
 typedef void(^SDImageCacheCalculateSizeBlock)(NSUInteger fileCount, NSUInteger totalSize);
 typedef NSString * _Nullable (^SDImageCacheAdditionalCachePathBlock)(NSString * _Nonnull key);
 typedef void(^SDImageCacheQueryCompletionBlock)(UIImage * _Nullable image, NSData * _Nullable data, SDImageCacheType cacheType);