fix(react-native): preserve ObjC block callback threads

Author: DjDeveloperr

NativeScript/ffi/shared/jsi/NativeApiJsiCallbacks.h

@@ -426,8 +426,8 @@ class NativeApiJsiCallback final
         gActiveSynchronousNativeInvocationDepth.load(
             std::memory_order_acquire) > 0;
     bool nativeCallerThreadCallback =
-        !currentThreadIsJs && activeSynchronousNativeInvocation &&
-        (!block_ || !returnsVoid);
+        !currentThreadIsJs &&
+        (block_ || (activeSynchronousNativeInvocation && !returnsVoid));
     bool direct = currentThreadIsJs ||
                   gExecutingDispatchedUINativeCall ||
                   gSynchronousNativeInvocationDepth > 0 ||

test/react-native/ffi-compat/App.tsx

@@ -762,6 +762,32 @@ function buildReactNativeIntegrationTests(): TestCase[] {
         assert(callbackRan, 'background callback did not run');
       },
     },
+    {
+      name: 'invokes Objective-C block callbacks on the native caller thread',
+      run() {
+        let callbackRan = false;
+        let callbackThreadHash: string | null = null;
+        const nativeThreadHash = g('TNSObjCTypes')
+          .alloc()
+          .init()
+          .methodWithSimpleBlockOnBackground((callerThreadHash: string) => {
+            callbackRan = true;
+            callbackThreadHash = String(g('NSThread').currentThread.hash);
+            assertEqual(
+              callbackThreadHash,
+              String(callerThreadHash),
+              'block callback JS native calls thread',
+            );
+          });
+
+        assert(callbackRan, 'background block callback did not run');
+        assertEqual(
+          callbackThreadHash,
+          String(nativeThreadHash),
+          'background block callback return thread',
+        );
+      },
+    },
     {
       name: 'runs UIKit native calls through runOnUI main-thread dispatch',
       async run() {

test/runtime/fixtures/Marshalling/TNSObjCTypes.h

@@ -21,6 +21,7 @@ typedef int (^NumberReturner)(int, int, int);
 - (void)methodWithStructOutParameter:(TNSOStruct*)value;
 
 - (void)methodWithSimpleBlock:(void (^)(void))block;
+- (NSString*)methodWithSimpleBlockOnBackground:(void (^)(NSString* callerThreadHash))block;
 - (void)methodWithComplexBlock:(id (^)(int, id, SEL, NSObject*, TNSOStruct))block;
 
 - (void)methodRetainingBlock:(void (^)(void))block;

test/runtime/fixtures/Marshalling/TNSObjCTypes.m

@@ -48,6 +48,18 @@ - (void)methodWithSimpleBlock:(void (^)(void))block {
     block();
 }
 
+- (NSString*)methodWithSimpleBlockOnBackground:(void (^)(NSString* callerThreadHash))block {
+    __block NSString* nativeThreadHash = nil;
+    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
+    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+        nativeThreadHash = [NSString stringWithFormat:@"%lu", (unsigned long)NSThread.currentThread.hash];
+        block(nativeThreadHash);
+        dispatch_semaphore_signal(semaphore);
+    });
+    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
+    return nativeThreadHash;
+}
+
 - (void)methodRetainingBlock:(void (^)(void))block {
     _retainedBlock = block;
 }