Add support for acquiring multiple locks at once (#958)

* Add ASLocking which supports -tryLock and taking multiple locks safely

* Better multi locking

* Assert about lock set capacity

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -428,6 +428,7 @@
 		CCEDDDD1200C488000FFCD0A /* ASConfiguration.m in Sources */ = {isa = PBXBuildFile; fileRef = CCEDDDD0200C488000FFCD0A /* ASConfiguration.m */; };
 		CCEDDDD9200C518800FFCD0A /* ASConfigurationTests.m in Sources */ = {isa = PBXBuildFile; fileRef = CCEDDDD8200C518800FFCD0A /* ASConfigurationTests.m */; };
 		CCF18FF41D2575E300DF5895 /* NSIndexSet+ASHelpers.h in Headers */ = {isa = PBXBuildFile; fileRef = CC4981BA1D1C7F65004E13CC /* NSIndexSet+ASHelpers.h */; settings = {ATTRIBUTES = (Private, ); }; };
+		CCF1FF5E20C4785000AAD8FC /* ASLocking.h in Headers */ = {isa = PBXBuildFile; fileRef = CCF1FF5D20C4785000AAD8FC /* ASLocking.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		DB55C2671C641AE4004EDCF5 /* ASContextTransitioning.h in Headers */ = {isa = PBXBuildFile; fileRef = DB55C2651C641AE4004EDCF5 /* ASContextTransitioning.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		DB7121BCD50849C498C886FB /* libPods-AsyncDisplayKitTests.a in Frameworks */ = {isa = PBXBuildFile; fileRef = EFA731F0396842FF8AB635EE /* libPods-AsyncDisplayKitTests.a */; };
 		DB78412E1C6BCE1600A9E2B4 /* _ASTransitionContext.m in Sources */ = {isa = PBXBuildFile; fileRef = DB55C2601C6408D6004EDCF5 /* _ASTransitionContext.m */; };
@@ -947,6 +948,7 @@
 		CCEDDDCE200C42A200FFCD0A /* ASConfigurationDelegate.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ASConfigurationDelegate.h; sourceTree = "<group>"; };
 		CCEDDDD0200C488000FFCD0A /* ASConfiguration.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = ASConfiguration.m; sourceTree = "<group>"; };
 		CCEDDDD8200C518800FFCD0A /* ASConfigurationTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = ASConfigurationTests.m; sourceTree = "<group>"; };
+		CCF1FF5D20C4785000AAD8FC /* ASLocking.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ASLocking.h; sourceTree = "<group>"; };
 		D3779BCFF841AD3EB56537ED /* Pods-AsyncDisplayKitTests.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-AsyncDisplayKitTests.release.xcconfig"; path = "Pods/Target Support Files/Pods-AsyncDisplayKitTests/Pods-AsyncDisplayKitTests.release.xcconfig"; sourceTree = "<group>"; };
 		D785F6601A74327E00291744 /* ASScrollNode.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASScrollNode.h; sourceTree = "<group>"; };
 		D785F6611A74327E00291744 /* ASScrollNode.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ASScrollNode.mm; sourceTree = "<group>"; };
@@ -1162,6 +1164,7 @@
 				058D09DD195D050800B7D73C /* ASImageNode.h */,
 				058D09DE195D050800B7D73C /* ASImageNode.mm */,
 				68355B2E1CB5799E001D4E68 /* ASImageNode+AnimatedImage.mm */,
+				CCF1FF5D20C4785000AAD8FC /* ASLocking.h */,
 				92DD2FE11BF4B97E0074C9DD /* ASMapNode.h */,
 				92DD2FE21BF4B97E0074C9DD /* ASMapNode.mm */,
 				0516FA3E1A1563D200B4EBED /* ASMultiplexImageNode.h */,
@@ -1871,6 +1874,7 @@
 				CC56013B1F06E9A700DC4FBE /* ASIntegerMap.h in Headers */,
 				B35061FA1B010EFD0018CF92 /* ASControlNode+Subclasses.h in Headers */,
 				E54E81FC1EB357BD00FFE8E1 /* ASPageTable.h in Headers */,
+				CCF1FF5E20C4785000AAD8FC /* ASLocking.h in Headers */,
 				B35061F81B010EFD0018CF92 /* ASControlNode.h in Headers */,
 				B35062171B010EFD0018CF92 /* ASDataController.h in Headers */,
 				34EFC75B1B701BAF00AD841F /* ASDimension.h in Headers */,

CHANGELOG.md

@@ -4,6 +4,7 @@
 - Make `ASPerformMainThreadDeallocation` visible in C. [Adlai Holler](https://github.com/Adlai-Holler)
 - 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)
 
 ## 2.7
 - Fix pager node for interface coalescing. [Max Wang](https://github.com/wsdwsd0829) [#877](https://github.com/TextureGroup/Texture/pull/877)

Source/ASDisplayNode.h

@@ -25,6 +25,7 @@
 #import <AsyncDisplayKit/ASAsciiArtBoxCreator.h>
 #import <AsyncDisplayKit/ASObjectDescriptionHelpers.h>
 #import <AsyncDisplayKit/ASLayoutElement.h>
+#import <AsyncDisplayKit/ASLocking.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -127,7 +128,7 @@ extern NSInteger const ASDefaultDrawingPriority;
  *
  */
 
-@interface ASDisplayNode : NSObject <NSLocking>
+@interface ASDisplayNode : NSObject <ASLocking>
 
 /** @name Initializing a node object */
 

Source/ASDisplayNode.mm

@@ -373,15 +373,7 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   return self;
 }
 
-- (void)lock
-{
-  __instanceLock__.lock();
-}
-
-- (void)unlock
-{
-  __instanceLock__.unlock();
-}
+ASSynthesizeLockingMethodsWithMutex(__instanceLock__);
 
 - (void)setViewBlock:(ASDisplayNodeViewBlock)viewBlock
 {

Source/ASLocking.h

@@ -0,0 +1,162 @@
+//
+//  ASLocking.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>
+#import <pthread/sched.h>
+
+#import <AsyncDisplayKit/ASAssert.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+#define kLockSetCapacity 32
+
+/**
+ * An extension of NSLocking that supports -tryLock.
+ */
+@protocol ASLocking <NSLocking>
+
+/// Try to take lock without blocking. Returns whether the lock was taken.
+- (BOOL)tryLock;
+
+@end
+
+/**
+ * A set of locks acquired during ASLockSequence.
+ */
+typedef struct {
+  unsigned count;
+  CFTypeRef _Nullable locks[kLockSetCapacity];
+} ASLockSet;
+
+/**
+ * Declare a lock set that is automatically unlocked at the end of scope.
+ *
+ * We use this instead of a scope-locking macro because we want to be able
+ * to step through the lock sequence block in the debugger.
+ */
+#define ASScopedLockSet __unused ASLockSet __attribute__((cleanup(ASUnlockSet)))
+
+/**
+ * A block that attempts to add a lock to a lock sequence.
+ * Such a block is provided to the caller of ASLockSequence.
+ *
+ * Returns whether the lock was added. You should return
+ * NO from your lock sequence body if it returns NO.
+ *
+ * For instance, you might write `return addLock(l1) && addLock(l2)`.
+ *
+ * @param lock The lock to attempt to add.
+ * @return YES if the lock was added, NO otherwise.
+ */
+typedef BOOL(^ASAddLockBlock)(id<ASLocking> lock);
+
+/**
+ * A block that attempts to lock multiple locks in sequence.
+ * Such a block is provided by the caller of ASLockSequence.
+ *
+ * The block may be run multiple times, if not all locks are immediately
+ * available. Therefore the block should be idempotent.
+ *
+ * The block should attempt to invoke addLock multiple times with
+ * different locks. It should return NO as soon as any addLock
+ * operation fails.
+ *
+ * For instance, you might write `return addLock(l1) && addLock(l2)`.
+ *
+ * @param addLock A block you can call to attempt to add a lock.
+ * @return YES if all locks were added, NO otherwise.
+ */
+typedef BOOL(^ASLockSequenceBlock)(NS_NOESCAPE ASAddLockBlock addLock);
+
+/**
+ * Unlock and release all of the locks in this lock set.
+ */
+NS_INLINE void ASUnlockSet(ASLockSet *lockSet) {
+  for (unsigned i = 0; i < lockSet->count; i++) {
+    CFTypeRef lock = lockSet->locks[i];
+    [(__bridge id<ASLocking>)lock unlock];
+    CFRelease(lock);
+  }
+}
+
+/**
+ * Take multiple locks "simultaneously," avoiding deadlocks
+ * caused by lock ordering.
+ *
+ * The block you provide should attempt to take a series of locks,
+ * using the provided `addLock` block. As soon as any addLock fails,
+ * you should return NO.
+ *
+ * For example:
+ * ASLockSequence(^(ASAddLockBlock addLock) ^{
+ *   return addLock(l0) && addLock(l1);
+ * });
+ *
+ * Note: This function doesn't protect from lock ordering deadlocks if
+ * one of the locks is already locked (recursive.) Only locks taken
+ * inside this function are guaranteed not to cause a deadlock.
+ */
+NS_INLINE ASLockSet ASLockSequence(NS_NOESCAPE ASLockSequenceBlock body)
+{
+  __block ASLockSet locks = (ASLockSet){0};
+  BOOL (^addLock)(id<ASLocking>) = ^(id<ASLocking> obj) {
+    
+    // nil lock = ignore.
+    if (!obj) {
+      return YES;
+    }
+    
+    // If they go over capacity, assert and return YES.
+    // If we return NO, they will enter an infinite loop.
+    if (locks.count == kLockSetCapacity) {
+      ASDisplayNodeCFailAssert(@"Locking more than %d locks at once is not supported.", kLockSetCapacity);
+      return YES;
+    }
+    
+    if ([obj tryLock]) {
+      locks.locks[locks.count++] = (__bridge_retained CFTypeRef)obj;
+      return YES;
+    }
+    return NO;
+  };
+  
+  /**
+   * Repeatedly try running their block, passing in our `addLock`
+   * until it succeeds. If it fails, unlock all and yield the thread
+   * to reduce spinning.
+   */
+  while (true) {
+    if (body(addLock)) {
+      // Success
+      return locks;
+    } else {
+      ASUnlockSet(&locks);
+      locks.count = 0;
+      sched_yield();
+    }
+  }
+}
+
+/**
+ * These Foundation classes already implement -tryLock.
+ */
+
+@interface NSLock (ASLocking) <ASLocking>
+@end
+
+@interface NSRecursiveLock (ASLocking) <ASLocking>
+@end
+
+@interface NSConditionLock (ASLocking) <ASLocking>
+@end
+
+NS_ASSUME_NONNULL_END

Source/ASRunLoopQueue.h

@@ -17,6 +17,7 @@
 
 #import <Foundation/Foundation.h>
 #import <AsyncDisplayKit/ASBaseDefines.h>
+#import <AsyncDisplayKit/ASLocking.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -28,7 +29,7 @@ NS_ASSUME_NONNULL_BEGIN
 @end
 
 AS_SUBCLASSING_RESTRICTED
-@interface ASRunLoopQueue<ObjectType> : ASAbstractRunLoopQueue <NSLocking>
+@interface ASRunLoopQueue<ObjectType> : ASAbstractRunLoopQueue <ASLocking>
 
 /**
  * Create a new queue with the given run loop and handler.

Source/ASRunLoopQueue.mm

@@ -541,17 +541,7 @@ typedef enum {
   return _internalQueue.count == 0;
 }
 
-#pragma mark - NSLocking
-
-- (void)lock
-{
-  _internalQueueLock.lock();
-}
-
-- (void)unlock
-{
-  _internalQueueLock.unlock();
-}
+ASSynthesizeLockingMethodsWithMutex(_internalQueueLock)
 
 @end
 

Source/AsyncDisplayKit.h

@@ -110,6 +110,7 @@
 #import <AsyncDisplayKit/ASHashing.h>
 #import <AsyncDisplayKit/ASHighlightOverlayLayer.h>
 #import <AsyncDisplayKit/ASImageContainerProtocolCategories.h>
+#import <AsyncDisplayKit/ASLocking.h>
 #import <AsyncDisplayKit/ASLog.h>
 #import <AsyncDisplayKit/ASMutableAttributedStringBuilder.h>
 #import <AsyncDisplayKit/ASRunLoopQueue.h>

Source/Details/ASThread.h

@@ -87,6 +87,16 @@ ASDISPLAYNODE_INLINE void _ASLockScopeUnownedCleanup(id<NSLocking> __unsafe_unre
   id<NSLocking> __lockToken __attribute__((cleanup(_ASUnlockScopeCleanup))) NS_VALID_UNTIL_END_OF_SCOPE = nsLocking; \
   [__lockToken unlock];
 
+#define ASSynthesizeLockingMethodsWithMutex(mutex) \
+- (void)lock { mutex.lock(); } \
+- (void)unlock { mutex.unlock(); } \
+- (BOOL)tryLock { return mutex.tryLock(); }
+
+#define ASSynthesizeLockingMethodsWithObject(object) \
+- (void)lock { [object lock]; } \
+- (void)unlock { [object unlock]; } \
+- (BOOL)tryLock { return [object tryLock]; }
+
 ASDISPLAYNODE_INLINE void _ASUnlockScopeCleanup(id<NSLocking> __strong *lockPtr) {
   [*lockPtr lock];
 }
@@ -265,6 +275,25 @@ namespace ASDN {
     Mutex (const Mutex&) = delete;
     Mutex &operator=(const Mutex&) = delete;
 
+    bool tryLock() {
+      if (gMutex_unfair) {
+        if (_recursive) {
+          return ASRecursiveUnfairLockTryLock(&_runfair);
+        } else {
+          return os_unfair_lock_trylock(&_unfair);
+        }
+      } else {
+        auto result = pthread_mutex_trylock(&_m);
+        if (result == 0) {
+          return true;
+        } else if (result == EBUSY) {
+          return false;
+        } else {
+          ASDisplayNodeCFailAssert(@"Locking error: %s", strerror(result));
+          return true; // if we return false we may enter an infinite loop.
+        }
+      }
+    }
     void lock() {
       if (gMutex_unfair) {
         if (_recursive) {

Source/Layout/ASLayoutElement.h

@@ -22,6 +22,7 @@
 #import <AsyncDisplayKit/ASAbsoluteLayoutElement.h>
 #import <AsyncDisplayKit/ASTraitCollection.h>
 #import <AsyncDisplayKit/ASAsciiArtBoxCreator.h>
+#import <AsyncDisplayKit/ASLocking.h>
 
 @class ASLayout;
 @class ASLayoutSpec;
@@ -174,7 +175,7 @@ extern NSString * const ASLayoutElementStyleLayoutPositionProperty;
 - (void)style:(__kindof ASLayoutElementStyle *)style propertyDidChange:(NSString *)propertyName;
 @end
 
-@interface ASLayoutElementStyle : NSObject <ASStackLayoutElement, ASAbsoluteLayoutElement, ASLayoutElementExtensibility, NSLocking>
+@interface ASLayoutElementStyle : NSObject <ASStackLayoutElement, ASAbsoluteLayoutElement, ASLayoutElementExtensibility, ASLocking>
 
 /**
  * @abstract Initializes the layoutElement style with a specified delegate

Source/Layout/ASLayoutElement.mm

@@ -176,17 +176,7 @@ do {\
   return self;
 }
 
-#pragma mark - NSLocking
-
-- (void)lock
-{
-  __instanceLock__.lock();
-}
-
-- (void)unlock
-{
-  __instanceLock__.unlock();
-}
+ASSynthesizeLockingMethodsWithMutex(__instanceLock__)
 
 #pragma mark - ASLayoutElementStyleSize
 

Source/Layout/ASLayoutSpec.h

@@ -17,6 +17,7 @@
 
 #import <AsyncDisplayKit/ASLayoutElement.h>
 #import <AsyncDisplayKit/ASAsciiArtBoxCreator.h>
+#import <AsyncDisplayKit/ASLocking.h>
 #import <AsyncDisplayKit/ASObjectDescriptionHelpers.h>
 
 NS_ASSUME_NONNULL_BEGIN
@@ -24,7 +25,7 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  * A layout spec is an immutable object that describes a layout, loosely inspired by React.
  */
-@interface ASLayoutSpec : NSObject <ASLayoutElement, ASLayoutElementStylability, NSFastEnumeration, ASDescriptionProvider, NSLocking>
+@interface ASLayoutSpec : NSObject <ASLayoutElement, ASLayoutElementStylability, NSFastEnumeration, ASDescriptionProvider, ASLocking>
 
 /** 
  * Creation of a layout spec should only happen by a user in layoutSpecThatFits:. During that method, a

Source/Layout/ASLayoutSpec.mm

@@ -259,17 +259,7 @@ ASLayoutElementStyleExtensibilityForwarding
   return result;
 }
 
-#pragma mark - NSLocking
-
-- (void)lock
-{
-  __instanceLock__.lock();
-}
-
-- (void)unlock
-{
-  __instanceLock__.unlock();
-}
+ASSynthesizeLockingMethodsWithMutex(__instanceLock__)
 
 @end