Implement cancellation for RCTAssetsLibraryImageLoader

Reviewed By: @tadeuzagallo Differential Revision: D2471253

Author: ndfred

Libraries/CameraRoll/RCTAssetsLibraryImageLoader.m

@@ -11,6 +11,7 @@
 
 #import <AssetsLibrary/AssetsLibrary.h>
 #import <ImageIO/ImageIO.h>
+#import <libkern/OSAtomic.h>
 #import <UIKit/UIKit.h>
 
 #import "RCTBridge.h"
@@ -45,17 +46,26 @@ - (BOOL)canLoadImageURL:(NSURL *)requestURL
 
 - (RCTImageLoaderCancellationBlock)loadImageForURL:(NSURL *)imageURL size:(CGSize)size scale:(CGFloat)scale resizeMode:(UIViewContentMode)resizeMode progressHandler:(RCTImageLoaderProgressBlock)progressHandler completionHandler:(RCTImageLoaderCompletionBlock)completionHandler
 {
+ __block volatile uint32_t cancelled = 0;
+
  [[self assetsLibrary] assetForURL:imageURL resultBlock:^(ALAsset *asset) {
+ if (cancelled) {
+ return;
+ }
+
  if (asset) {
  // ALAssetLibrary API is async and will be multi-threaded. Loading a few full
  // resolution images at once will spike the memory up to store the image data,
  // and might trigger memory warnings and/or OOM crashes.
  // To improve this, process the loaded asset in a serial queue.
  dispatch_async(RCTAssetsLibraryImageLoaderQueue(), ^{
+ if (cancelled) {
+ return;
+ }
+
  // Also make sure the image is released immediately after it's used so it
  // doesn't spike the memory up during the process.
  @autoreleasepool {
-
  BOOL useMaximumSize = CGSizeEqualToSize(size, CGSizeZero);
  ALAssetRepresentation *representation = [asset defaultRepresentation];
 
@@ -78,12 +88,18 @@ - (RCTImageLoaderCancellationBlock)loadImageForURL:(NSURL *)imageURL size:(CGSiz
  completionHandler(error, nil);
  }
  } failureBlock:^(NSError *loadError) {
+ if (cancelled) {
+ return;
+ }
+
  NSString *errorText = [NSString stringWithFormat:@"Failed to load asset at URL %@.\niOS Error: %@", imageURL, loadError];
  NSError *error = RCTErrorWithMessage(errorText);
  completionHandler(error, nil);
  }];
 
- return ^{};
+ return ^{
+ OSAtomicOr32Barrier(1, &cancelled);
+ };
 }
 
 @end