Merge pull request #1839 from maicki/MSAsyncMeasure

[ASDisplayNode] Allow measure always be off the main thread

Author: Adlai Holler

AsyncDisplayKit/ASDisplayNode.mm

@@ -15,6 +15,7 @@
 
 #import <objc/runtime.h>
 #import <deque>
+#import <queue>
 
 #import "_ASAsyncTransaction.h"
 #import "_ASAsyncTransactionContainer+Private.h"
@@ -631,7 +632,7 @@ - (ASLayout *)measureWithSizeRange:(ASSizeRange)constrainedSize
   if (! [self shouldMeasureWithSizeRange:constrainedSize]) {
     return _layout;
   }
-
+  
   [self cancelLayoutTransitionsInProgress];
 
   ASLayout *previousLayout = _layout;
@@ -642,13 +643,14 @@ - (ASLayout *)measureWithSizeRange:(ASSizeRange)constrainedSize
                                                           pendingLayout:newLayout
                                                          previousLayout:previousLayout];
   } else {
-    ASLayoutTransition *layoutContext;
+    ASLayoutTransition *layoutTransition = nil;
     if (self.usesImplicitHierarchyManagement) {
-      layoutContext = [[ASLayoutTransition alloc] initWithNode:self
-                                                 pendingLayout:newLayout
-                                                previousLayout:previousLayout];
+      layoutTransition = [[ASLayoutTransition alloc] initWithNode:self
+                                                    pendingLayout:newLayout
+                                                   previousLayout:previousLayout];
     }
-    [self applyLayout:newLayout layoutContext:layoutContext];
+    
+    [self _applyLayout:newLayout layoutTransition:layoutTransition];
     [self _completeLayoutCalculation];
   }
 
@@ -685,6 +687,11 @@ - (ASLayoutableType)layoutableType
   return ASLayoutableTypeDisplayNode;
 }
 
+- (BOOL)canLayoutAsynchronous
+{
+  return !self.isNodeLoaded;
+}
+
 #pragma mark - Layout Transition
 
 - (void)transitionLayoutWithAnimation:(BOOL)animated
@@ -716,7 +723,7 @@ - (void)transitionLayoutWithSizeRange:(ASSizeRange)constrainedSize
   int32_t transitionID = [self _startNewTransition];
 
   ASDisplayNodePerformBlockOnEverySubnode(self, ^(ASDisplayNode * _Nonnull node) {
-    ASDisplayNodeAssert([node _hasTransitionInProgress] == NO, @"Can't start a transition when one of the subnodes is performing one.");
+    ASDisplayNodeAssert([node _isTransitionInProgress] == NO, @"Can't start a transition when one of the subnodes is performing one.");
     node.hierarchyState |= ASHierarchyStateLayoutPending;
     node.pendingTransitionID = transitionID;
   });
@@ -755,10 +762,10 @@ - (void)transitionLayoutWithSizeRange:(ASSizeRange)constrainedSize
       }
 
       ASLayout *previousLayout = _layout;
-      [self applyLayout:newLayout layoutContext:nil];
+      [self _applyLayout:newLayout layoutTransition:nil];
 
       ASDisplayNodePerformBlockOnEverySubnode(self, ^(ASDisplayNode * _Nonnull node) {
-        [node applyPendingLayoutContext];
+        [node _applyPendingLayoutContext];
         [node _completeLayoutCalculation];
         node.hierarchyState &= (~ASHierarchyStateLayoutPending);
       });
@@ -781,6 +788,7 @@ - (void)transitionLayoutWithSizeRange:(ASSizeRange)constrainedSize
     });
   };
 
+  // TODO ihm: Can we always push the measure to the background thread and remove the parameter from the API?
   if (shouldMeasureAsync) {
     ASPerformBlockOnBackgroundThread(transitionBlock);
   } else {
@@ -818,7 +826,7 @@ - (void)calculatedLayoutDidChange
 - (void)cancelLayoutTransitionsInProgress
 {
   ASDN::MutexLocker l(_propertyLock);
-  if ([self _hasTransitionInProgress]) {
+  if ([self _isTransitionInProgress]) {
     // Cancel transition in progress
     [self _finishOrCancelTransition];
 
@@ -841,10 +849,10 @@ - (void)setUsesImplicitHierarchyManagement:(BOOL)value
   _usesImplicitHierarchyManagement = value;
 }
 
-- (BOOL)_hasTransitionInProgress
+- (BOOL)_isTransitionInProgress
 {
-    ASDN::MutexLocker l(_propertyLock);
-    return _transitionInProgress;
+  ASDN::MutexLocker l(_propertyLock);
+  return _transitionInProgress;
 }
 
 /// Starts a new transition and returns the transition id
@@ -2412,16 +2420,16 @@ - (void)exitHierarchyState:(ASHierarchyState)hierarchyState
   });
 }
 
-- (void)applyPendingLayoutContext
+- (void)_applyPendingLayoutContext
 {
   ASDN::MutexLocker l(_propertyLock);
   if (_pendingLayoutTransition) {
-    [self applyLayout:_pendingLayoutTransition.pendingLayout layoutContext:_pendingLayoutTransition];
+    [self _applyLayout:_pendingLayoutTransition.pendingLayout layoutTransition:_pendingLayoutTransition];
     _pendingLayoutTransition = nil;
   }
 }
 
-- (void)applyLayout:(ASLayout *)layout layoutContext:(ASLayoutTransition *)layoutContext
+- (void)_applyLayout:(ASLayout *)layout layoutTransition:(ASLayoutTransition *)layoutTransition
 {
   ASDN::MutexLocker l(_propertyLock);
   _layout = layout;
@@ -2430,10 +2438,22 @@ - (void)applyLayout:(ASLayout *)layout layoutContext:(ASLayoutTransition *)layou
   ASDisplayNodeAssertTrue(layout.size.width >= 0.0);
   ASDisplayNodeAssertTrue(layout.size.height >= 0.0);
 
-  if (self.usesImplicitHierarchyManagement && layoutContext != nil) {
-    [layoutContext applySubnodeInsertions];
-    [layoutContext applySubnodeRemovals];
+  if (layoutTransition == nil || self.usesImplicitHierarchyManagement == NO) {
+    return;
   }
+
+  // Trampoline to the main thread if necessary
+  if (ASDisplayNodeThreadIsMain() == NO && layoutTransition.isSynchronous == NO) {
+
+    // Subnode insertions and removals need to happen always on the main thread if at least one subnode is already loaded
+    ASPerformBlockOnMainThread(^{
+      [layoutTransition startTransition];
+    });
+    
+    return;
+  }
+  
+  [layoutTransition startTransition];
 }
 
 - (void)layout

AsyncDisplayKit/Layout/ASLayoutSpec.mm

@@ -54,6 +54,11 @@ - (ASLayoutableType)layoutableType
   return ASLayoutableTypeLayoutSpec;
 }
 
+- (BOOL)canLayoutAsynchronous
+{
+  return YES;
+}
+
 #pragma mark - Layout
 
 - (ASLayout *)measureWithSizeRange:(ASSizeRange)constrainedSize

AsyncDisplayKit/Layout/ASLayoutable.h

@@ -46,8 +46,16 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @protocol ASLayoutable <ASEnvironment, ASStackLayoutable, ASStaticLayoutable, ASLayoutablePrivate, ASLayoutableExtensibility>
 
+/**
+ * @abstract Returns type of layoutable
+ */
 @property (nonatomic, readonly) ASLayoutableType layoutableType;
 
+/**
+ * @abstract Returns if the layoutable can be used to layout in an asynchronous way on a background thread.
+ */
+@property (nonatomic, readonly) BOOL canLayoutAsynchronous;
+
 /**
  * @abstract Calculate a layout based on given size range.
  *

AsyncDisplayKit/Private/ASDisplayNodeInternal.h

@@ -118,6 +118,7 @@ FOUNDATION_EXPORT NSString * const ASRenderingEngineDidDisplayNodesScheduledBefo
   ASEnvironmentState _environmentState;
   ASLayout *_layout;
 
+
   UIEdgeInsets _hitTestSlop;
   NSMutableArray *_subnodes;
 

AsyncDisplayKit/Private/ASLayoutTransition.h

@@ -18,16 +18,45 @@
 
 @interface ASLayoutTransition : NSObject <_ASTransitionContextLayoutDelegate>
 
+/**
+ * Node to apply layout transition on
+ */
 @property (nonatomic, readonly, weak) ASDisplayNode *node;
-@property (nonatomic, readonly, strong) ASLayout *pendingLayout;
+
+/**
+ * Previous layout to transition from
+ */
 @property (nonatomic, readonly, strong) ASLayout *previousLayout;
 
-- (instancetype)initWithNode:(ASDisplayNode *)node
-               pendingLayout:(ASLayout *)pendingLayout
-              previousLayout:(ASLayout *)previousLayout;
+/**
+ * Pending layout to transition to
+ */
+@property (nonatomic, readonly, strong) ASLayout *pendingLayout;
 
+/**
+ * Returns if the layout transition can happen asynchronously
+ */
+@property (nonatomic, readonly, assign) BOOL isSynchronous;
+
+/**
+ * Returns a newly initialized layout transition
+ */
+- (instancetype)initWithNode:(ASDisplayNode *)node pendingLayout:(ASLayout *)pendingLayout previousLayout:(ASLayout *)previousLayout NS_DESIGNATED_INITIALIZER;
+- (instancetype)init NS_UNAVAILABLE;
+
+/**
+ * Insert and remove subnodes that where added or removed between the previousLayout and the pendingLayout
+ */
+- (void)startTransition;
+
+/**
+ * Insert all new subnodes that where added between the previous layout and the pending layout
+ */
 - (void)applySubnodeInsertions;
 
+/**
+ * Remove all subnodes that are removed between the previous layout and the pending layout
+ */
 - (void)applySubnodeRemovals;
 
 @end

AsyncDisplayKit/Private/ASLayoutTransition.mm

@@ -18,10 +18,37 @@
 #import "ASLayout.h"
 
 #import <vector>
+#import <queue>
 
 #import "NSArray+Diffing.h"
 #import "ASEqualityHelpers.h"
 
+/**
+ * Search the whole layout stack if at least one layout has a layoutable object that can not be layed out asynchronous.
+ * This can be the case for example if a node was already loaded
+ */
+static inline BOOL ASLayoutCanTransitionAsynchronous(ASLayout *layout) {
+  // Queue used to keep track of sublayouts while traversing this layout in a BFS fashion.
+  std::queue<ASLayout *> queue;
+  queue.push(layout);
+  
+  while (!queue.empty()) {
+    layout = queue.front();
+    queue.pop();
+    
+    if (layout.layoutableObject.canLayoutAsynchronous == NO) {
+      return NO;
+    }
+    
+    // Add all sublayouts to process in next step
+    for (int i = 0; i < layout.sublayouts.count; i++) {
+      queue.push(layout.sublayouts[0]);
+    }
+  }
+  
+  return YES;
+}
+
 @implementation ASLayoutTransition {
   ASDN::RecursiveMutex _propertyLock;
   BOOL _calculatedSubnodeOperations;
@@ -44,6 +71,18 @@ - (instancetype)initWithNode:(ASDisplayNode *)node
   return self;
 }
 
+- (BOOL)isSynchronous
+{
+  ASDN::MutexLocker l(_propertyLock);
+  return ASLayoutCanTransitionAsynchronous(_pendingLayout);
+}
+
+- (void)startTransition
+{
+  [self applySubnodeInsertions];
+  [self applySubnodeRemovals];
+}
+
 - (void)applySubnodeInsertions
 {
   ASDN::MutexLocker l(_propertyLock);

AsyncDisplayKitTests/ASDisplayNodeImplicitHierarchyTests.m

@@ -130,4 +130,88 @@ - (void)testCalculatedLayoutHierarchyTransitions
   XCTAssertEqual(node.subnodes[2], node2);
 }
 
+- (void)testMeasurementInBackgroundThreadWithLoadedNode
+{
+  ASDisplayNode *node1 = [[ASDisplayNode alloc] init];
+  ASDisplayNode *node2 = [[ASDisplayNode alloc] init];
+  
+  ASSpecTestDisplayNode *node = [[ASSpecTestDisplayNode alloc] init];
+  node.layoutSpecBlock = ^(ASDisplayNode *weakNode, ASSizeRange constrainedSize) {
+    ASSpecTestDisplayNode *strongNode = (ASSpecTestDisplayNode *)weakNode;
+    if ([strongNode.layoutState isEqualToNumber:@1]) {
+      return [ASStaticLayoutSpec staticLayoutSpecWithChildren:@[node1]];
+    } else {
+      return [ASStaticLayoutSpec staticLayoutSpecWithChildren:@[node2]];
+    }
+  };
+  
+  // Intentionally trigger view creation
+  [node2 view];
+  
+  XCTestExpectation *expectation = [self expectationWithDescription:@"Fix IHM layout also if one node is already loaded"];
+  
+  dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+    
+    [node measureWithSizeRange:ASSizeRangeMake(CGSizeZero, CGSizeZero)];
+    XCTAssertEqual(node.subnodes[0], node1);
+    
+    node.layoutState = @2;
+    [node invalidateCalculatedLayout];
+    [node measureWithSizeRange:ASSizeRangeMake(CGSizeZero, CGSizeZero)];
+    
+    // Dispatch back to the main thread to let the insertion / deletion of subnodes happening
+    dispatch_async(dispatch_get_main_queue(), ^{
+      XCTAssertEqual(node.subnodes[0], node2);
+      [expectation fulfill];
+    });
+  });
+  
+  [self waitForExpectationsWithTimeout:5.0 handler:^(NSError *error) {
+    if (error) {
+      NSLog(@"Timeout Error: %@", error);
+    }
+  }];
+}
+
+- (void)testTransitionLayoutWithAnimationWithLoadedNodes
+{
+  ASDisplayNode *node1 = [[ASDisplayNode alloc] init];
+  ASDisplayNode *node2 = [[ASDisplayNode alloc] init];
+  
+  ASSpecTestDisplayNode *node = [[ASSpecTestDisplayNode alloc] init];
+  
+  node.layoutSpecBlock = ^(ASDisplayNode *weakNode, ASSizeRange constrainedSize) {
+    ASSpecTestDisplayNode *strongNode = (ASSpecTestDisplayNode *)weakNode;
+    if ([strongNode.layoutState isEqualToNumber:@1]) {
+      return [ASStaticLayoutSpec staticLayoutSpecWithChildren:@[node1]];
+    } else {
+      return [ASStaticLayoutSpec staticLayoutSpecWithChildren:@[node2]];
+    }
+  };
+ 
+  // Intentionally trigger view creation
+  [node2 view];
+  
+  XCTestExpectation *expectation = [self expectationWithDescription:@"Fix IHM layout transition also if one node is already loaded"];
+  
+  [node measureWithSizeRange:ASSizeRangeMake(CGSizeZero, CGSizeZero)];
+  XCTAssertEqual(node.subnodes[0], node1);
+  
+  node.layoutState = @2;
+  [node invalidateCalculatedLayout];
+  [node transitionLayoutWithAnimation:YES shouldMeasureAsync:YES measurementCompletion:^{
+    // Push this to the next runloop to let async insertion / removing of nodes finished before checking
+    dispatch_async(dispatch_get_main_queue(), ^{
+      XCTAssertEqual(node.subnodes[0], node2);
+      [expectation fulfill];
+    });
+  }];
+  
+  [self waitForExpectationsWithTimeout:5.0 handler:^(NSError *error) {
+    if (error) {
+      NSLog(@"Timeout Error: %@", error);
+    }
+  }];
+}
+
 @end