Measure performance for ASCellNode layout (#2209)

* Measure performance for ASCellNode layout

* Address Adlai and Levi's feedback:
* Move to ASDisplayNode level
* Lock around setting/getting measurement options and results
* Record all measurement passes and report times as an array
* Only add relevant entries to the performanceMetrics dictionary
* Rebase

* Store sum and count instead of array

* Rename ScopeTimerDataPoint to ScopeTimerSum

* Address Levi's feedback

* Address Adlai's feedback

AsyncDisplayKit/ASDisplayNode+Beta.h

@@ -18,6 +18,22 @@ void ASPerformBlockOnMainThread(void (^block)());
 void ASPerformBlockOnBackgroundThread(void (^block)()); // DISPATCH_QUEUE_PRIORITY_DEFAULT
 ASDISPLAYNODE_EXTERN_C_END
 
+/**
+ * Bitmask to indicate what performance measurements the cell should record.
+ */
+typedef NS_OPTIONS(NSUInteger, ASDisplayNodePerformanceMeasurementOptions) {
+  ASDisplayNodePerformanceMeasurementOptionLayoutSpec = 1 << 0,
+  ASDisplayNodePerformanceMeasurementOptionLayoutGeneration = 1 << 1
+};
+
+/**
+ * Keys to retrieve performance entries from the performance dictionary.
+ */
+extern NSString *const ASDisplayNodeLayoutSpecTotalTimeKey;
+extern NSString *const ASDisplayNodeLayoutSpecNumberOfPassesKey;
+extern NSString *const ASDisplayNodeLayoutGenerationTotalTimeKey;
+extern NSString *const ASDisplayNodeLayoutGenerationNumberOfPassesKey;
+
 @interface ASDisplayNode (Beta)
 
 /**
@@ -57,6 +73,17 @@ ASDISPLAYNODE_EXTERN_C_END
  */
 @property (nonatomic, copy, nullable) ASDisplayNodeContextModifier didDisplayNodeContentWithRenderingContext;
 
+/**
+ * @abstract A bitmask representing which actions (layout spec, layout generation) should be measured.
+ */
+@property (nonatomic, assign) ASDisplayNodePerformanceMeasurementOptions measurementOptions;
+
+/**
+ * @abstract A dictionary representing performance measurements collected.
+ * @note see the constants above to retrieve relevant performance measurements
+ */
+@property (nonatomic, strong, readonly) NSDictionary *performanceMeasurements;
+
 /** @name Layout Transitioning */
 
 /**

AsyncDisplayKit/ASDisplayNode.mm

@@ -38,6 +38,11 @@
 NSInteger const ASDefaultDrawingPriority = ASDefaultTransactionPriority;
 NSString * const ASRenderingEngineDidDisplayScheduledNodesNotification = @"ASRenderingEngineDidDisplayScheduledNodes";
 NSString * const ASRenderingEngineDidDisplayNodesScheduledBeforeTimestamp = @"ASRenderingEngineDidDisplayNodesScheduledBeforeTimestamp";
+NSString * const ASDisplayNodeLayoutSpecTotalTimeKey = @"ASDisplayNodeLayoutSpecTotalTime";
+NSString * const ASDisplayNodeLayoutSpecNumberOfPassesKey = @"ASDisplayNodeLayoutSpecNumberOfPasses";
+NSString * const ASDisplayNodeLayoutGenerationTotalTimeKey = @"ASDisplayNodeLayoutGenerationTotalTime";
+NSString * const ASDisplayNodeLayoutGenerationNumberOfPassesKey = @"ASDisplayNodeLayoutGenerationNumberOfPasses";
+
 
 // Forward declare CALayerDelegate protocol as the iOS 10 SDK moves CALayerDelegate from a formal delegate to a protocol.
 // We have to forward declare the protocol as this place otherwise it will not compile compiling with an Base SDK < iOS 10
@@ -1156,6 +1161,33 @@ ASLayoutableSizeHelperForwarding
   // subclass override
 }
 
+- (void)setMeasurementOptions:(ASDisplayNodePerformanceMeasurementOptions)measurementOptions
+{
+  ASDN::MutexLocker l(__instanceLock__);
+  _measurementOptions = measurementOptions;
+}
+
+- (ASDisplayNodePerformanceMeasurementOptions)measurementOptions
+{
+  ASDN::MutexLocker l(__instanceLock__);
+  return _measurementOptions;
+}
+
+- (NSDictionary *)performanceMeasurements
+{
+  ASDN::MutexLocker l(__instanceLock__);
+  NSMutableDictionary *measurements = [NSMutableDictionary dictionaryWithCapacity:4];
+  if (_measurementOptions & ASDisplayNodePerformanceMeasurementOptionLayoutSpec) {
+    measurements[ASDisplayNodeLayoutSpecTotalTimeKey] = @(_layoutSpecTotalTime);
+    measurements[ASDisplayNodeLayoutSpecNumberOfPassesKey] = @(_layoutSpecNumberOfPasses);
+  }
+  if (_measurementOptions & ASDisplayNodePerformanceMeasurementOptionLayoutGeneration) {
+    measurements[ASDisplayNodeLayoutGenerationTotalTimeKey] = @(_layoutGenerationTotalTime);
+    measurements[ASDisplayNodeLayoutGenerationNumberOfPassesKey] = @(_layoutGenerationNumberOfPasses);
+  }
+  return measurements;
+}
+
 #pragma mark - Asynchronous display
 
 - (BOOL)displaysAsynchronously
@@ -2343,7 +2375,15 @@ void recursivelyTriggerDisplayForLayer(CALayer *layer, BOOL shouldBlock)
 
   ASDN::MutexLocker l(__instanceLock__);
   if ((_methodOverrides & ASDisplayNodeMethodOverrideLayoutSpecThatFits) || _layoutSpecBlock != NULL) {
-    ASLayoutSpec *layoutSpec = [self layoutSpecThatFits:constrainedSize];
+    ASLayoutSpec *layoutSpec = nil;
+    // optional performance measurement for cell nodes
+    if (_measurementOptions & ASDisplayNodePerformanceMeasurementOptionLayoutSpec) {
+      ASDN::SumScopeTimer t(_layoutSpecTotalTime);
+      _layoutSpecNumberOfPasses++;
+      layoutSpec = [self layoutSpecThatFits:constrainedSize];
+    } else {
+      layoutSpec = [self layoutSpecThatFits:constrainedSize];
+    }
 
     ASDisplayNodeAssert(layoutSpec.isMutable, @"Node %@ returned layout spec %@ that has already been used. Layout specs should always be regenerated.", self, layoutSpec);
 
@@ -2353,7 +2393,16 @@ void recursivelyTriggerDisplayForLayer(CALayer *layer, BOOL shouldBlock)
     ASEnvironmentStatePropagateDown(layoutSpec, self.environmentTraitCollection);
     
     layoutSpec.isMutable = NO;
-    ASLayout *layout = [layoutSpec layoutThatFits:constrainedSize];
+    ASLayout *layout = nil;
+    // optional performance measurement for cell nodes
+    if (_measurementOptions & ASDisplayNodePerformanceMeasurementOptionLayoutGeneration) {
+      ASDN::SumScopeTimer t(_layoutGenerationTotalTime);
+      _layoutGenerationNumberOfPasses++;
+      layout = [layoutSpec layoutThatFits:constrainedSize];
+    } else {
+      layout = [layoutSpec layoutThatFits:constrainedSize];
+    }
+
     ASDisplayNodeAssertNotNil(layout, @"[ASLayoutSpec measureWithSizeRange:] should never return nil! %@, %@", self, layoutSpec);
       
     // Make sure layoutableObject of the root layout is `self`, so that the flattened layout will be structurally correct.

AsyncDisplayKit/Private/ASDisplayNodeInternal.h

@@ -22,6 +22,8 @@
 #import "ASEnvironment.h"
 #import "ASObjectDescriptionHelpers.h"
 
+#import "ASDisplayNode+Beta.h"
+
 @protocol _ASDisplayLayerDelegate;
 @class _ASDisplayLayer;
 @class _ASPendingState;
@@ -163,6 +165,13 @@ FOUNDATION_EXPORT NSString * const ASRenderingEngineDidDisplayNodesScheduledBefo
   CGPoint _accessibilityActivationPoint;
   UIBezierPath *_accessibilityPath;
 
+  // performance measurement
+  ASDisplayNodePerformanceMeasurementOptions _measurementOptions;
+  NSTimeInterval _layoutSpecTotalTime;
+  NSUInteger _layoutSpecNumberOfPasses;
+  NSTimeInterval _layoutGenerationTotalTime;
+  NSUInteger _layoutGenerationNumberOfPasses;
+
 #if TIME_DISPLAYNODE_OPS
 @public
   NSTimeInterval _debugTimeToCreateView;

AsyncDisplayKit/Private/_ASScopeTimer.h

@@ -37,4 +37,16 @@ namespace ASDN {
       outT = CACurrentMediaTime() - begin;
     }
   };
+
+  // variant where repeated calls are summed
+  struct SumScopeTimer {
+    NSTimeInterval begin;
+    NSTimeInterval &outT;
+    SumScopeTimer(NSTimeInterval &outRef) : outT(outRef) {
+      begin = CACurrentMediaTime();
+    }
+    ~SumScopeTimer() {
+      outT += CACurrentMediaTime() - begin;
+    }
+  };
 }