From a2913d33a66dc1d179ced170d6c73c8ddf91960e Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Sat, 1 Jun 2019 20:04:27 -0700
Subject: [PATCH] Fabric: The second attempt to fix a thread-safety issue in
 RCTNativeAnimatedModule

Summary:
Previously we tried to fix that with RCTUnsafeExecuteOnUIManagerQueueSync but that caused a deadlock (yeah, it's actually unsafe).
Besides that, I tried to solve that with introducing a mutex that covers access to `_operations` and `_preOperations` but failed miserably. It solved threading issue but that didn't fix data-races and inconsistency of the collections.

Reviewed By: sahrens

Differential Revision: D15587564

fbshipit-source-id: d1953036b09354d1663a9b191440f8b4a4e6be9d
---
 .../NativeAnimation/RCTNativeAnimatedModule.m | 28 +++++++++++--------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/Libraries/NativeAnimation/RCTNativeAnimatedModule.m b/Libraries/NativeAnimation/RCTNativeAnimatedModule.m
index 69bf078f804..0bbc9c78711 100644
--- a/Libraries/NativeAnimation/RCTNativeAnimatedModule.m
+++ b/Libraries/NativeAnimation/RCTNativeAnimatedModule.m
@@ -232,27 +232,31 @@ RCT_EXPORT_METHOD(removeAnimatedEventFromView:(nonnull NSNumber *)viewTag
 - (void)willMountComponentsWithRootTag:(NSInteger)rootTag
 {
   RCTAssertMainQueue();
-  __block NSArray<AnimatedOperation> *preOperations;
-  RCTUnsafeExecuteOnUIManagerQueueSync(^{
-    preOperations = self->_preOperations;
+  RCTExecuteOnUIManagerQueue(^{
+    NSArray<AnimatedOperation> *preOperations = self->_preOperations;
     self->_preOperations = [NSMutableArray new];
+
+    RCTExecuteOnMainQueue(^{
+      for (AnimatedOperation preOperation in preOperations) {
+        preOperation(self->_nodesManager);
+      }
+    });
   });
-  for (AnimatedOperation operation in preOperations) {
-    operation(self->_nodesManager);
-  }
 }
 
 - (void)didMountComponentsWithRootTag:(NSInteger)rootTag
 {
   RCTAssertMainQueue();
-  __block NSArray<AnimatedOperation> *operations;
-  RCTUnsafeExecuteOnUIManagerQueueSync(^{
-    operations = self->_operations;
+  RCTExecuteOnUIManagerQueue(^{
+    NSArray<AnimatedOperation> *operations = self->_operations;
     self->_operations = [NSMutableArray new];
+
+    RCTExecuteOnMainQueue(^{
+      for (AnimatedOperation operation in operations) {
+        operation(self->_nodesManager);
+      }
+    });
   });
-  for (AnimatedOperation operation in operations) {
-    operation(self->_nodesManager);
-  }
 }
 
 #pragma mark - RCTUIManagerObserver