Reduce _ASAsyncTransaction allocations by ensuring nodes without disp…

…lay methods don't create them.

AsyncDisplayKit/Private/ASDisplayNode+AsyncDisplay.mm

@@ -308,16 +308,14 @@ - (void)displayAsyncLayer:(_ASDisplayLayer *)asyncLayer asynchronously:(BOOL)asy
     return BOOL(displaySentinelValue != displaySentinel.value);
   };
 
-  // If we're participating in an ancestor's asyncTransaction, find it here
-  ASDisplayNodeAssert(_layer, @"Expect _layer to be not nil");
-  CALayer *containerLayer = _layer.asyncdisplaykit_parentTransactionContainer ?: _layer;
-  _ASAsyncTransaction *transaction = containerLayer.asyncdisplaykit_asyncTransaction;
-
   // Set up displayBlock to call either display or draw on the delegate and return a UIImage contents
   asyncdisplaykit_async_transaction_operation_block_t displayBlock = [self _displayBlockWithAsynchronous:asynchronously isCancelledBlock:isCancelledBlock rasterizing:NO];
+
   if (!displayBlock) {
     return;
   }
+
+  ASDisplayNodeAssert(_layer, @"Expect _layer to be not nil");
 
   // This block is called back on the main thread after rendering at the completion of the current async transaction, or immediately if !asynchronously
   asyncdisplaykit_async_transaction_operation_completion_block_t completionBlock = ^(id<NSObject> value, BOOL canceled){
@@ -335,16 +333,27 @@ - (void)displayAsyncLayer:(_ASDisplayLayer *)asyncLayer asynchronously:(BOOL)asy
     }
   };
 
-  if (displayBlock != NULL) {
-    // Call willDisplay immediately in either case
-    [self willDisplayAsyncLayer:self.asyncLayer];
+  // Call willDisplay immediately in either case
+  [self willDisplayAsyncLayer:self.asyncLayer];
 
-    if (asynchronously) {
-      [transaction addOperationWithBlock:displayBlock queue:[_ASDisplayLayer displayQueue] completion:completionBlock];
-    } else {
-      UIImage *contents = (UIImage *)displayBlock();
-      completionBlock(contents, NO);
-    }
+  if (asynchronously) {
+    // Async rendering operations are contained by a transaction, which allows them to proceed and concurrently
+    // while synchronizing the final application of the results to the layer's contents property (completionBlock).
+
+    // First, look to see if we are expected to join a parent's transaction container.
+    CALayer *containerLayer = _layer.asyncdisplaykit_parentTransactionContainer ?: _layer;
+
+    // In the case that a transaction does not yet exist (such as for an individual node outside of a container),
+    // this call will allocate the transaction and add it to _ASAsyncTransactionGroup.
+    // It will automatically commit the transaction at the end of the runloop.
+    _ASAsyncTransaction *transaction = containerLayer.asyncdisplaykit_asyncTransaction;
+
+    // Adding this displayBlock operation to the transaction will start it IMMEDIATELY.
+    // The only function of the transaction commit is to gate the calling of the completionBlock.
+    [transaction addOperationWithBlock:displayBlock queue:[_ASDisplayLayer displayQueue] completion:completionBlock];
+  } else {
+    UIImage *contents = (UIImage *)displayBlock();
+    completionBlock(contents, NO);
   }
 }
 

Podfile.lock

@@ -10,4 +10,4 @@ SPEC CHECKSUMS:
   FBSnapshotTestCase: 3dc3899168747a0319c5278f5b3445c13a6532dd
   OCMock: a6a7dc0e3997fb9f35d99f72528698ebf60d64f2
 
-COCOAPODS: 0.37.2
+COCOAPODS: 0.38.2

examples/Kittens/Sample/KittenNode.mm

@@ -38,7 +38,7 @@ @interface KittenNode ()
 
 @implementation KittenNode
 
-// lorem ipsum text courtesy http://kittyipsum.com/ <3
+// lorem ipsum text courtesy https://kittyipsum.com/ <3
 + (NSArray *)placeholders
 {
   static NSArray *placeholders = nil;
@@ -82,7 +82,7 @@ - (instancetype)initWithKittenOfSize:(CGSize)size
   // kitten image, with a solid background colour serving as placeholder
   _imageNode = [[ASNetworkImageNode alloc] init];
   _imageNode.backgroundColor = ASDisplayNodeDefaultPlaceholderColor();
-  _imageNode.URL = [NSURL URLWithString:[NSString stringWithFormat:@"http://placekitten.com/%zd/%zd",
+  _imageNode.URL = [NSURL URLWithString:[NSString stringWithFormat:@"https://placekitten.com/%zd/%zd",
                                                                    (NSInteger)roundl(_kittenSize.width),
                                                                    (NSInteger)roundl(_kittenSize.height)]];
 //  _imageNode.contentMode = UIViewContentModeCenter;