[ASImageNode] Always dealloc images in a background queue (#561)

* ASImageNode to always dealloc its images in a background queue

* Update CHANGELOG

CHANGELOG.md

@@ -19,8 +19,10 @@
 - [ASDisplayNode] Ensure `-displayWillStartAsynchronously:` and `-displayDidFinish` are invoked on rasterized subnodes.  [Eric Scheers](https://github.com/smeis) [#532](https://github.com/TextureGroup/Texture/pull/532)
 - Fixed a memory corruption issue in the ASImageNode display system. [Adlai Holler](https://github.com/Adlai-Holler) [#555](https://github.com/TextureGroup/Texture/pull/555)
 - [Breaking] Rename ASCollectionGalleryLayoutSizeProviding to ASCollectionGalleryLayoutPropertiesProviding. Besides a fixed item size, it now can provide interitem and line spacings, as well as section inset [Huy Nguyen](https://github.com/nguyenhuy) [#496](https://github.com/TextureGroup/Texture/pull/496) [#533](https://github.com/TextureGroup/Texture/pull/533)
-- Deprecate `-[ASDisplayNode displayWillStart]` in favor of `-displayWillStartAsynchronously:` [Huy Nguyen](https://github.com/nguyenhuy) [536](https://github.com/TextureGroup/Texture/pull/536)
+- Deprecate `-[ASDisplayNode displayWillStart]` in favor of `-displayWillStartAsynchronously:` [Huy Nguyen](https://github.com/nguyenhuy) [#536](https:/
+/github.com/TextureGroup/Texture/pull/536)
 - Add support for URLs on ASNetworkImageNode. [Garrett Moon](https://github.com/garrettmoon)
+- [ASImageNode] Always dealloc images in a background queue [Huy Nguyen](https://github.com/nguyenhuy) [#561](https://github.com/TextureGroup/Texture/pull/561)
 - Mark ASRunLoopQueue as drained if it contains only NULLs [Cesar Estebanez](https://github.com/cesteban) [#558](https://github.com/TextureGroup/Texture/pull/558)
 
 ##2.4

Source/ASImageNode.mm

@@ -41,6 +41,8 @@
 
 #include <functional>
 
+static const CGSize kMinReleaseImageOnBackgroundSize = {20.0, 20.0};
+
 typedef void (^ASImageNodeDrawParametersBlock)(ASWeakMapEntry *entry);
 
 @interface ASImageNodeDrawParameters : NSObject {
@@ -248,11 +250,11 @@ typedef void (^ASImageNodeDrawParametersBlock)(ASWeakMapEntry *entry);
   if (ASObjectIsEqual(_image, image)) {
     return;
   }
-  
+
+  UIImage *oldImage = _image;
   _image = image;
   
   if (image != nil) {
-    
     // We explicitly call setNeedsDisplay in this case, although we know setNeedsDisplay will be called with lock held.
     // Therefore we have to be careful in methods that are involved with setNeedsDisplay to not run into a deadlock
     [self setNeedsDisplay];
@@ -265,10 +267,19 @@ typedef void (^ASImageNodeDrawParametersBlock)(ASWeakMapEntry *entry);
         [self addSubnode:_debugLabelNode];
       });
     }
-
   } else {
     self.contents = nil;
   }
+
+  // Destruction of bigger images on the main thread can be expensive
+  // and can take some time, so we dispatch onto a bg queue to
+  // actually dealloc.
+  CGSize oldImageSize = oldImage.size;
+  BOOL shouldReleaseImageOnBackgroundThread = oldImageSize.width > kMinReleaseImageOnBackgroundSize.width
+                                              || oldImageSize.height > kMinReleaseImageOnBackgroundSize.height;
+  if (shouldReleaseImageOnBackgroundThread) {
+    ASPerformBackgroundDeallocation(oldImage);
+  }
 }
 
 - (UIImage *)image

Source/ASNetworkImageNode.mm

@@ -32,8 +32,6 @@
 #import <AsyncDisplayKit/ASPINRemoteImageDownloader.h>
 #endif
 
-static const CGSize kMinReleaseImageOnBackgroundSize = {20.0, 20.0};
-
 @interface ASNetworkImageNode ()
 {
   // Only access any of these with __instanceLock__.
@@ -521,21 +519,9 @@ static const CGSize kMinReleaseImageOnBackgroundSize = {20.0, 20.0};
 {
   [self _locked_cancelImageDownloadWithResumePossibility:storeResume];
   
-  // Destruction of bigger images on the main thread can be expensive
-  // and can take some time, so we dispatch onto a bg queue to
-  // actually dealloc.
-  UIImage *image = [self _locked_Image];
-  UIImage *defaultImage = _defaultImage;
-  CGSize imageSize = image.size;
-  BOOL shouldReleaseImageOnBackgroundThread = imageSize.width > kMinReleaseImageOnBackgroundSize.width ||
-                                              imageSize.height > kMinReleaseImageOnBackgroundSize.height;
-  if (shouldReleaseImageOnBackgroundThread) {
-    ASPerformBackgroundDeallocation(image);
-  }
-
   [self _locked_setAnimatedImage:nil];
   [self _locked_setCurrentImageQuality:0.0];
-  [self _locked__setImage:defaultImage];
+  [self _locked__setImage:_defaultImage];
 
   _imageLoaded = NO;