Generalize the main thread ivar deallocation system

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -393,6 +393,8 @@
 		CCB1F95C1EFB6350009C7475 /* ASSignpost.h in Headers */ = {isa = PBXBuildFile; fileRef = CCB1F95B1EFB6316009C7475 /* ASSignpost.h */; };
 		CCB2F34D1D63CCC6004E6DE9 /* ASDisplayNodeSnapshotTests.m in Sources */ = {isa = PBXBuildFile; fileRef = CCB2F34C1D63CCC6004E6DE9 /* ASDisplayNodeSnapshotTests.m */; };
 		CCBBBF5D1EB161760069AA91 /* ASRangeManagingNode.h in Headers */ = {isa = PBXBuildFile; fileRef = CCBBBF5C1EB161760069AA91 /* ASRangeManagingNode.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		CCBDDD0520C62A2D00CBA922 /* ASMainThreadDeallocation.h in Headers */ = {isa = PBXBuildFile; fileRef = CCBDDD0320C62A2D00CBA922 /* ASMainThreadDeallocation.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		CCBDDD0620C62A2D00CBA922 /* ASMainThreadDeallocation.mm in Sources */ = {isa = PBXBuildFile; fileRef = CCBDDD0420C62A2D00CBA922 /* ASMainThreadDeallocation.mm */; };
 		CCCCCCD51EC3EF060087FE10 /* ASTextDebugOption.h in Headers */ = {isa = PBXBuildFile; fileRef = CCCCCCC31EC3EF060087FE10 /* ASTextDebugOption.h */; };
 		CCCCCCD61EC3EF060087FE10 /* ASTextDebugOption.m in Sources */ = {isa = PBXBuildFile; fileRef = CCCCCCC41EC3EF060087FE10 /* ASTextDebugOption.m */; };
 		CCCCCCD71EC3EF060087FE10 /* ASTextInput.h in Headers */ = {isa = PBXBuildFile; fileRef = CCCCCCC51EC3EF060087FE10 /* ASTextInput.h */; };
@@ -907,6 +909,8 @@
 		CCBBBF5C1EB161760069AA91 /* ASRangeManagingNode.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASRangeManagingNode.h; sourceTree = "<group>"; };
 		CCBD05DE1E4147B000D18509 /* ASIGListAdapterBasedDataSource.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASIGListAdapterBasedDataSource.m; sourceTree = "<group>"; };
 		CCBD05DF1E4147B000D18509 /* ASIGListAdapterBasedDataSource.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASIGListAdapterBasedDataSource.h; sourceTree = "<group>"; };
+		CCBDDD0320C62A2D00CBA922 /* ASMainThreadDeallocation.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ASMainThreadDeallocation.h; sourceTree = "<group>"; };
+		CCBDDD0420C62A2D00CBA922 /* ASMainThreadDeallocation.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = ASMainThreadDeallocation.mm; sourceTree = "<group>"; };
 		CCCCCCC31EC3EF060087FE10 /* ASTextDebugOption.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASTextDebugOption.h; sourceTree = "<group>"; };
 		CCCCCCC41EC3EF060087FE10 /* ASTextDebugOption.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASTextDebugOption.m; sourceTree = "<group>"; };
 		CCCCCCC51EC3EF060087FE10 /* ASTextInput.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASTextInput.h; sourceTree = "<group>"; };
@@ -1165,6 +1169,8 @@
 				058D09DE195D050800B7D73C /* ASImageNode.mm */,
 				68355B2E1CB5799E001D4E68 /* ASImageNode+AnimatedImage.mm */,
 				CCF1FF5D20C4785000AAD8FC /* ASLocking.h */,
+				CCBDDD0320C62A2D00CBA922 /* ASMainThreadDeallocation.h */,
+				CCBDDD0420C62A2D00CBA922 /* ASMainThreadDeallocation.mm */,
 				92DD2FE11BF4B97E0074C9DD /* ASMapNode.h */,
 				92DD2FE21BF4B97E0074C9DD /* ASMapNode.mm */,
 				0516FA3E1A1563D200B4EBED /* ASMultiplexImageNode.h */,
@@ -1822,6 +1828,7 @@
 				693A1DCA1ECC944E00D0C9D2 /* IGListAdapter+AsyncDisplayKit.h in Headers */,
 				E5E2D72E1EA780C4005C24C6 /* ASCollectionGalleryLayoutDelegate.h in Headers */,
 				E58E9E461E941D74004CFC59 /* ASCollectionLayoutDelegate.h in Headers */,
+				CCBDDD0520C62A2D00CBA922 /* ASMainThreadDeallocation.h in Headers */,
 				CCAA0B7F206ADBF30057B336 /* ASRecursiveUnfairLock.h in Headers */,
 				E5E281741E71C833006B67C2 /* ASCollectionLayoutState.h in Headers */,
 				E5B077FF1E69F4EB00C24B5B /* ASElementMap.h in Headers */,
@@ -2377,6 +2384,7 @@
 				B35061F91B010EFD0018CF92 /* ASControlNode.mm in Sources */,
 				8021EC1F1D2B00B100799119 /* UIImage+ASConvenience.m in Sources */,
 				CCAA0B80206ADBF30057B336 /* ASRecursiveUnfairLock.m in Sources */,
+				CCBDDD0620C62A2D00CBA922 /* ASMainThreadDeallocation.mm in Sources */,
 				B35062181B010EFD0018CF92 /* ASDataController.mm in Sources */,
 				CCB1F95A1EFB60A5009C7475 /* ASLog.m in Sources */,
 				767E7F8E1C90191D0066C000 /* AsyncDisplayKit+Debug.m in Sources */,

CHANGELOG.md

@@ -5,6 +5,7 @@
 - Add snapshot test for astextnode2. [Max Wang](https://github.com/wsdwsd0829) [#935](https://github.com/TextureGroup/Texture/pull/935)
 - Internal housekeeping on the async transaction (rendering) system. [Adlai Holler](https://github.com/Adlai-Holler)
 - Add new protocol `ASLocking` that extends `NSLocking` with `tryLock`, and allows taking multiple locks safely. [Adlai Holler](https://github.com/Adlai-Holler)
+- Make the main thread ivar deallocation system available to other classes. Plus a little optimization. See `ASMainThreadDeallocation.h`. [Adlai Holler](https://github.com/Adlai-Holler) [#959](https://github.com/TextureGroup/Texture/pull/959)
 
 ## 2.7
 - Fix pager node for interface coalescing. [Max Wang](https://github.com/wsdwsd0829) [#877](https://github.com/TextureGroup/Texture/pull/877)

Source/ASDisplayNode.mm

@@ -44,6 +44,7 @@
 #import <AsyncDisplayKit/ASLayoutSpec.h>
 #import <AsyncDisplayKit/ASLayoutSpecPrivate.h>
 #import <AsyncDisplayKit/ASLog.h>
+#import <AsyncDisplayKit/ASMainThreadDeallocation.h>
 #import <AsyncDisplayKit/ASRunLoopQueue.h>
 #import <AsyncDisplayKit/ASSignpost.h>
 #import <AsyncDisplayKit/ASTraitCollection.h>
@@ -428,124 +429,12 @@ - (void)dealloc
   for (ASDisplayNode *subnode in _subnodes)
     [subnode _setSupernode:nil];
 
-  // Trampoline any UIKit ivars' deallocation to main
-  if (ASDisplayNodeThreadIsMain() == NO) {
-    [self _scheduleIvarsForMainDeallocation];
-  }
+  [self scheduleIvarsForMainThreadDeallocation];
 
   // TODO: Remove this? If supernode isn't already nil, this method isn't dealloc-safe anyway.
   [self _setSupernode:nil];
 }
 
-- (void)_scheduleIvarsForMainDeallocation
-{
-  NSValue *ivarsObj = [[self class] _ivarsThatMayNeedMainDeallocation];
-
-  // Unwrap the ivar array
-  unsigned int count = 0;
-  // Will be unused if assertions are disabled.
-  __unused int scanResult = sscanf(ivarsObj.objCType, "[%u^{objc_ivar}]", &count);
-  ASDisplayNodeAssert(scanResult == 1, @"Unexpected type in NSValue: %s", ivarsObj.objCType);
-  Ivar ivars[count];
-  [ivarsObj getValue:ivars];
-
-  for (Ivar ivar : ivars) {
-    id value = object_getIvar(self, ivar);
-    if (value == nil) {
-      continue;
-    }
-
-    if (ASClassRequiresMainThreadDeallocation(object_getClass(value))) {
-      as_log_debug(ASMainThreadDeallocationLog(), "%@: Trampolining ivar '%s' value %@ for main deallocation.", self, ivar_getName(ivar), value);
-
-      // Before scheduling the ivar for main thread deallocation we have clear out the ivar, otherwise we can run
-      // into a race condition where the main queue is drained earlier than this node is deallocated and the ivar
-      // is still deallocated on a background thread
-      object_setIvar(self, ivar, nil);
-
-      ASPerformMainThreadDeallocation(&value);
-    } else {
-      as_log_debug(ASMainThreadDeallocationLog(), "%@: Not trampolining ivar '%s' value %@.", self, ivar_getName(ivar), value);
-    }
-  }
-}
-
-/**
- * Returns an NSValue-wrapped array of all the ivars in this class or its superclasses
- * up through ASDisplayNode, that we expect may need to be deallocated on main.
- * 
- * This method caches its results.
- *
- * Result is of type NSValue<[Ivar]>
- */
-+ (NSValue * _Nonnull)_ivarsThatMayNeedMainDeallocation NS_RETURNS_RETAINED
-{
-  static NSCache<Class, NSValue *> *ivarsCache;
-  static dispatch_once_t onceToken;
-  dispatch_once(&onceToken, ^{
-    ivarsCache = [[NSCache alloc] init];
-  });
-
-  NSValue *result = [ivarsCache objectForKey:self];
-  if (result != nil) {
-    return result;
-  }
-
-  // Cache miss.
-  unsigned int resultCount = 0;
-  static const int kMaxDealloc2MainIvarsPerClassTree = 64;
-  Ivar resultIvars[kMaxDealloc2MainIvarsPerClassTree];
-
-  // Get superclass results first.
-  Class c = class_getSuperclass(self);
-  if (c != [NSObject class]) {
-    NSValue *ivarsObj = [c _ivarsThatMayNeedMainDeallocation];
-    // Unwrap the ivar array and append it to our working array
-    unsigned int count = 0;
-    // Will be unused if assertions are disabled.
-    __unused int scanResult = sscanf(ivarsObj.objCType, "[%u^{objc_ivar}]", &count);
-    ASDisplayNodeAssert(scanResult == 1, @"Unexpected type in NSValue: %s", ivarsObj.objCType);
-    ASDisplayNodeCAssert(resultCount + count < kMaxDealloc2MainIvarsPerClassTree, @"More than %d dealloc2main ivars are not supported. Count: %d", kMaxDealloc2MainIvarsPerClassTree, resultCount + count);
-    [ivarsObj getValue:resultIvars + resultCount];
-    resultCount += count;
-  }
-
-  // Now gather ivars from this particular class.
-  unsigned int allMyIvarsCount;
-  Ivar *allMyIvars = class_copyIvarList(self, &allMyIvarsCount);
-
-  for (NSUInteger i = 0; i < allMyIvarsCount; i++) {
-    Ivar ivar = allMyIvars[i];
-    const char *type = ivar_getTypeEncoding(ivar);
-
-    if (type != NULL && strcmp(type, @encode(id)) == 0) {
-      // If it's `id` we have to include it just in case.
-      resultIvars[resultCount] = ivar;
-      resultCount += 1;
-      as_log_debug(ASMainThreadDeallocationLog(), "%@: Marking ivar '%s' for possible main deallocation due to type id", self, ivar_getName(ivar));
-    } else {
-      // If it's an ivar with a static type, check the type.
-      Class c = ASGetClassFromType(type);
-      if (ASClassRequiresMainThreadDeallocation(c)) {
-        resultIvars[resultCount] = ivar;
-        resultCount += 1;
-        as_log_debug(ASMainThreadDeallocationLog(), "%@: Marking ivar '%s' for main deallocation due to class %@", self, ivar_getName(ivar), c);
-      } else {
-        as_log_debug(ASMainThreadDeallocationLog(), "%@: Skipping ivar '%s' for main deallocation.", self, ivar_getName(ivar));
-      }
-    }
-  }
-  free(allMyIvars);
-
-  // Encode the type (array of Ivars) into a string and wrap it in an NSValue
-  char arrayType[32];
-  snprintf(arrayType, 32, "[%u^{objc_ivar}]", resultCount);
-  result = [NSValue valueWithBytes:resultIvars objCType:arrayType];
-
-  [ivarsCache setObject:result forKey:self];
-  return result;
-}
-
 #pragma mark - Loading
 
 - (BOOL)_locked_shouldLoadViewOrLayer

Source/ASDisplayNodeExtras.mm

@@ -36,6 +36,9 @@ extern void ASPerformMainThreadDeallocation(id _Nullable __strong * _Nonnull obj
   });
 
   if (objectPtr != NULL && *objectPtr != nil) {
+    // TODO: If ASRunLoopQueue supported an "unsafe_unretained" mode, we could
+    // transfer the caller's +1 into it and save the retain/release pair.
+
     // Lock queue while enqueuing and releasing, so that there's no risk
     // that the queue will release before we get a chance to release.
     [queue lock];

Source/ASMainThreadDeallocation.h

@@ -0,0 +1,47 @@
+//
+//  ASMainThreadDeallocation.h
+//  Texture
+//
+//  Copyright (c) 2018-present, Pinterest, Inc.  All rights reserved.
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface NSObject (ASMainThreadIvarTeardown)
+
+/**
+ * Call this from -dealloc to schedule this instance's
+ * ivars for main thread deallocation as needed.
+ *
+ * This method includes a check for whether it's on the main thread,
+ * and it will do nothing in that case.
+ */
+- (void)scheduleIvarsForMainThreadDeallocation;
+
+@end
+
+@interface NSObject (ASNeedsMainThreadDeallocation)
+
+/**
+ * Override this property to indicate that instances of this
+ * class need to be deallocated on the main thread.
+ * You do not access this property yourself.
+ *
+ * The NSObject implementation returns NO if the class name has
+ * a prefix UI, AV, or CA. This property is also overridden to
+ * return fixed values for other common classes, such as UIImage,
+ * UIGestureRecognizer, and UIResponder.
+ */
+@property (class, readonly) BOOL needsMainThreadDeallocation;
+
+@end
+
+
+NS_ASSUME_NONNULL_END