Add a Flag to Disable Main Thread Assertions #trivial (#348)

* Add a thread-flag for disabling main thread assertions

* Fix the license header

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -369,6 +369,7 @@
 		CCA282CD1E9EB73E0037E8B7 /* ASTipNode.m in Sources */ = {isa = PBXBuildFile; fileRef = CCA282CB1E9EB73E0037E8B7 /* ASTipNode.m */; };
 		CCA282D01E9EBF6C0037E8B7 /* ASTipsWindow.h in Headers */ = {isa = PBXBuildFile; fileRef = CCA282CE1E9EBF6C0037E8B7 /* ASTipsWindow.h */; };
 		CCA282D11E9EBF6C0037E8B7 /* ASTipsWindow.m in Sources */ = {isa = PBXBuildFile; fileRef = CCA282CF1E9EBF6C0037E8B7 /* ASTipsWindow.m */; };
+		CCA5F62E1EECC2A80060C137 /* ASAssert.m in Sources */ = {isa = PBXBuildFile; fileRef = CCA5F62D1EECC2A80060C137 /* ASAssert.m */; };
 		CCA5F62C1EEC9E9B0060C137 /* NSInvocation+ASTestHelpers.m in Sources */ = {isa = PBXBuildFile; fileRef = CCA5F62B1EEC9E9B0060C137 /* NSInvocation+ASTestHelpers.m */; };
 		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, ); }; };
@@ -826,6 +827,7 @@
 		CCA282CB1E9EB73E0037E8B7 /* ASTipNode.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASTipNode.m; sourceTree = "<group>"; };
 		CCA282CE1E9EBF6C0037E8B7 /* ASTipsWindow.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASTipsWindow.h; sourceTree = "<group>"; };
 		CCA282CF1E9EBF6C0037E8B7 /* ASTipsWindow.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASTipsWindow.m; sourceTree = "<group>"; };
+		CCA5F62D1EECC2A80060C137 /* ASAssert.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASAssert.m; sourceTree = "<group>"; };
 		CCA5F62A1EEC9E9B0060C137 /* NSInvocation+ASTestHelpers.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "NSInvocation+ASTestHelpers.h"; sourceTree = "<group>"; };
 		CCA5F62B1EEC9E9B0060C137 /* NSInvocation+ASTestHelpers.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "NSInvocation+ASTestHelpers.m"; sourceTree = "<group>"; };
 		CCB2F34C1D63CCC6004E6DE9 /* ASDisplayNodeSnapshotTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASDisplayNodeSnapshotTests.m; sourceTree = "<group>"; };
@@ -1368,6 +1370,7 @@
 			isa = PBXGroup;
 			children = (
 				058D0A43195D058D00B7D73C /* ASAssert.h */,
+				CCA5F62D1EECC2A80060C137 /* ASAssert.m */,
 				0516FA3A1A15563400B4EBED /* ASAvailability.h */,
 				058D0A44195D058D00B7D73C /* ASBaseDefines.h */,
 				1950C4481A3BB5C1005C8279 /* ASEqualityHelpers.h */,
@@ -2088,6 +2091,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				DEB8ED7C1DD003D300DBDE55 /* ASLayoutTransition.mm in Sources */,
+				CCA5F62E1EECC2A80060C137 /* ASAssert.m in Sources */,
 				9F98C0261DBE29E000476D92 /* ASControlTargetAction.m in Sources */,
 				9C70F2091CDABA36007D6C76 /* ASViewController.mm in Sources */,
 				3917EBD51E9C2FC400D04A01 /* _ASCollectionReusableView.m in Sources */,

Source/ASDisplayNode.mm

@@ -3224,7 +3224,10 @@ ASDISPLAYNODE_INLINE BOOL subtreeIsRasterized(ASDisplayNode *node) {
 
 - (NSString *)debugDescription
 {
-  return ASObjectDescriptionMake(self, [self propertiesForDebugDescription]);
+  ASPushMainThreadAssertionsDisabled();
+  auto result = ASObjectDescriptionMake(self, [self propertiesForDebugDescription]);
+  ASPopMainThreadAssertionsDisabled();
+  return result;
 }
 
 // This should only be called for debugging. It's not thread safe and it doesn't assert.

Source/Base/ASAssert.h

@@ -19,6 +19,7 @@
 
 #import <Foundation/NSException.h>
 #import <pthread.h>
+#import <AsyncDisplayKit/ASBaseDefines.h>
 
 #define ASDISPLAYNODE_ASSERTIONS_ENABLED (!defined(NS_BLOCK_ASSERTIONS))
 
@@ -42,8 +43,8 @@
 #define ASDisplayNodeAssertNotInstantiable() ASDisplayNodeAssert(NO, nil, @"This class is not instantiable.");
 #define ASDisplayNodeAssertNotSupported() ASDisplayNodeAssert(NO, nil, @"This method is not supported by class %@", [self class]);
 
-#define ASDisplayNodeAssertMainThread() ASDisplayNodeAssert(0 != pthread_main_np(), @"This method must be called on the main thread")
+#define ASDisplayNodeAssertMainThread() ASDisplayNodeAssert(ASMainThreadAssertionsAreDisabled() || 0 != pthread_main_np(), @"This method must be called on the main thread")
-#define ASDisplayNodeCAssertMainThread() ASDisplayNodeCAssert(0 != pthread_main_np(), @"This function must be called on the main thread")
+#define ASDisplayNodeCAssertMainThread() ASDisplayNodeCAssert(ASMainThreadAssertionsAreDisabled() || 0 != pthread_main_np(), @"This function must be called on the main thread")
 
 #define ASDisplayNodeAssertNotMainThread() ASDisplayNodeAssert(0 == pthread_main_np(), @"This method must be called off the main thread")
 #define ASDisplayNodeCAssertNotMainThread() ASDisplayNodeCAssert(0 == pthread_main_np(), @"This function must be called off the main thread")
@@ -69,6 +70,23 @@
 #define ASDisplayNodeErrorDomain @"ASDisplayNodeErrorDomain"
 #define ASDisplayNodeNonFatalErrorCode 1
 
+/**
+ * In debug methods, it can be useful to disable main thread assertions to get valuable information,
+ * even if it means violating threading requirements. These functions are used in -debugDescription and let
+ * threads decide to suppress/re-enable main thread assertions.
+ */
+#pragma mark - Main Thread Assertions Disabling
+
+ASDISPLAYNODE_EXTERN_C_BEGIN
+BOOL ASMainThreadAssertionsAreDisabled();
+
+void ASPushMainThreadAssertionsDisabled();
+
+void ASPopMainThreadAssertionsDisabled();
+ASDISPLAYNODE_EXTERN_C_END
+
+#pragma mark - Non-Fatal Assertions
+
 /// Returns YES if assertion passed, NO otherwise.
 #define ASDisplayNodeAssertNonFatal(condition, desc, ...) ({                                                                      \
   BOOL __evaluated = condition;                                                                                                   \

Source/Base/ASAssert.m

@@ -0,0 +1,45 @@
+//
+//  ASAssert.m
+//  Texture
+//
+//  Copyright (c) 2017-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 <AsyncDisplayKit/ASAssert.h>
+#import <Foundation/Foundation.h>
+
+// pthread_key_create must be called before the key can be used. This function does that.
+static pthread_key_t ASMainThreadAssertionsDisabledKey()
+{
+  static pthread_key_t ASMainThreadAssertionsDisabledKey;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    pthread_key_create(&ASMainThreadAssertionsDisabledKey, NULL);
+  });
+  return ASMainThreadAssertionsDisabledKey;
+}
+
+BOOL ASMainThreadAssertionsAreDisabled() {
+  return (size_t)pthread_getspecific(ASMainThreadAssertionsDisabledKey()) > 0;
+}
+
+void ASPushMainThreadAssertionsDisabled() {
+  pthread_key_t key = ASMainThreadAssertionsDisabledKey();
+  size_t oldValue = (size_t)pthread_getspecific(key);
+  pthread_setspecific(key, (void *)(oldValue + 1));
+}
+
+void ASPopMainThreadAssertionsDisabled() {
+  pthread_key_t key = ASMainThreadAssertionsDisabledKey();
+  size_t oldValue = (size_t)pthread_getspecific(key);
+  if (oldValue > 0) {
+    pthread_setspecific(key, (void *)(oldValue - 1));
+  } else {
+    ASDisplayNodeCFailAssert(@"Attempt to pop thread assertion-disabling without corresponding push.");
+  }
+}

Tests/ASDisplayNodeTests.mm

@@ -2260,4 +2260,23 @@ static bool stringContainsPointer(NSString *description, id p) {
   ASXCTAssertEqualPoints([node convertPoint:node.bounds.origin toNode:nil], expectedOrigin);
 }
 
+- (void)testThatItIsAllowedToRetrieveDebugDescriptionIncludingVCOffMainThread
+{
+  ASDisplayNode *node = [[ASDisplayNode alloc] init];
+  UIViewController *vc = [[UIViewController alloc] init];
+  [vc.view addSubnode:node];
+  dispatch_group_t g = dispatch_group_create();
+  dispatch_group_enter(g);
+  __block NSString *debugDescription;
+  [NSThread detachNewThreadWithBlock:^{
+    debugDescription = [node debugDescription];
+    dispatch_group_leave(g);
+  }];
+  dispatch_group_wait(g, DISPATCH_TIME_FOREVER);
+  // Ensure the debug description contains the VC string.
+  // Have to split into two lines because XCTAssert macro can't handle the stringWithFormat:.
+  BOOL hasVC = [debugDescription containsString:[NSString stringWithFormat:@"%p", vc]];
+  XCTAssert(hasVC);
+}
+
 @end