Add experiment to skip creating UIViews altogether for constants (#881)

* Add experiment to skip creating UIViews altogether for constants

* Update changelog

* Do it right

* Annotate function

* Skip all the work entirely

CHANGELOG.md

@@ -45,6 +45,7 @@
 - Use `NS_RETURNS_RETAINED` macro to make our methods a tiny bit faster. [Adlai Holler](https://github.com/Adlai-Holler) [#843](https://github.com/TextureGroup/Texture/pull/843/)
 - `ASDisplayNode, ASLayoutSpec, and ASLayoutElementStyle` now conform to `NSLocking`. They act as recursive locks. Useful locking macros have been added as `ASThread.h`. Subclasses / client code can lock these objects but should be careful as usual when dealing with locks. [Adlai Holler](https://github.com/Adlai-Holler)
 - Introduces `ASRecursiveUnfairLock` as an experiment to improve locking performance. [Adlai Holler](https://github.com/Adlai-Holler)
+- Adds an experiment to shorten init time. [Adlai Holler](https://github.com/Adlai-Holler)
 
 ## 2.6
 - [Xcode 9] Updated to require Xcode 9 (to fix warnings) [Garrett Moon](https://github.com/garrettmoon)

Source/ASExperimentalFeatures.h

@@ -24,6 +24,7 @@ typedef NS_OPTIONS(NSUInteger, ASExperimentalFeatures) {
   ASExperimentalTextNode = 1 << 1,                          // exp_text_node
   ASExperimentalInterfaceStateCoalescing = 1 << 2,          // exp_interface_state_coalesce
   ASExperimentalUnfairLock = 1 << 3,                        // exp_unfair_lock
+  ASExperimentalLayerDefaults = 1 << 4,                     // exp_infer_layer_defaults
   ASExperimentalFeatureAll = 0xFFFFFFFF
 };
 

Source/ASExperimentalFeatures.m

@@ -16,7 +16,9 @@ NSArray<NSString *> *ASExperimentalFeaturesGetNames(ASExperimentalFeatures flags
 {
   NSArray *allNames = ASCreateOnce((@[@"exp_graphics_contexts",
                                       @"exp_text_node",
-                                      @"exp_interface_state_coalesce"]));
+                                      @"exp_interface_state_coalesce",
+                                      @"exp_unfair_lock",
+                                      @"exp_infer_layer_defaults"]));
   
   if (flags == ASExperimentalFeatureAll) {
     return allNames;

Source/Details/ASThread.h

@@ -29,7 +29,7 @@
 #import <AsyncDisplayKit/ASConfigurationInternal.h>
 #import <AsyncDisplayKit/ASRecursiveUnfairLock.h>
 
-ASDISPLAYNODE_INLINE BOOL ASDisplayNodeThreadIsMain()
+ASDISPLAYNODE_INLINE AS_WARN_UNUSED_RESULT BOOL ASDisplayNodeThreadIsMain()
 {
   return 0 != pthread_main_np();
 }

Source/Private/ASInternalHelpers.m

@@ -25,26 +25,42 @@
 #import <AsyncDisplayKit/ASRunLoopQueue.h>
 #import <AsyncDisplayKit/ASThread.h>
 
-static BOOL defaultAllowsGroupOpacity = YES;
-static BOOL defaultAllowsEdgeAntialiasing = NO;
+static NSNumber *allowsGroupOpacityFromUIKitOrNil;
+static NSNumber *allowsEdgeAntialiasingFromUIKitOrNil;
+
+BOOL ASDefaultAllowsGroupOpacity()
+{
+  static BOOL groupOpacity;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    NSNumber *groupOpacityObj = allowsGroupOpacityFromUIKitOrNil ?: [NSBundle.mainBundle objectForInfoDictionaryKey:@"UIViewGroupOpacity"];
+    groupOpacity = groupOpacityObj ? groupOpacityObj.boolValue : YES;
+  });
+  return groupOpacity;
+}
+
+BOOL ASDefaultAllowsEdgeAntialiasing()
+{
+  static BOOL edgeAntialiasing;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    NSNumber *antialiasingObj = allowsEdgeAntialiasingFromUIKitOrNil ?: [NSBundle.mainBundle objectForInfoDictionaryKey:@"UIViewEdgeAntialiasing"];
+    edgeAntialiasing = antialiasingObj ? antialiasingObj.boolValue : NO;
+  });
+  return edgeAntialiasing;
+}
 
 void ASInitializeFrameworkMainThread(void)
 {
-  ASDisplayNodeThreadIsMain();
+  ASDisplayNodeCAssertMainThread();
   // Ensure these values are cached on the main thread before needed in the background.
+  if (ASActivateExperimentalFeature(ASExperimentalLayerDefaults)) {
+    // Nop. We will gather default values on-demand in ASDefaultAllowsGroupOpacity and ASDefaultAllowsEdgeAntialiasing
+  } else {
     CALayer *layer = [[[UIView alloc] init] layer];
-  defaultAllowsGroupOpacity = layer.allowsGroupOpacity;
-  defaultAllowsEdgeAntialiasing = layer.allowsEdgeAntialiasing;
+    allowsGroupOpacityFromUIKitOrNil = @(layer.allowsGroupOpacity);
+    allowsEdgeAntialiasingFromUIKitOrNil = @(layer.allowsEdgeAntialiasing);
   }
-
-BOOL ASDefaultAllowsGroupOpacity(void)
-{
-  return defaultAllowsGroupOpacity;
-}
-
-BOOL ASDefaultAllowsEdgeAntialiasing(void)
-{
-  return defaultAllowsEdgeAntialiasing;
 }
 
 BOOL ASSubclassOverridesSelector(Class superclass, Class subclass, SEL selector)