Make sure both find and register are guarded for race condition

PiperOrigin-RevId: 253870928

Author: chkuang-g

instance_id/src/android/instance_id.cc

@@ -309,6 +309,7 @@ Future<void> InstanceId::DeleteToken(const char* entity, const char* scope) {
 InstanceId* InstanceId::GetInstanceId(App* app, InitResult* init_result_out) {
   FIREBASE_ASSERT_MESSAGE_RETURN(nullptr, app, "App must be specified.");
   FIREBASE_UTIL_RETURN_NULL_IF_GOOGLE_PLAY_UNAVAILABLE(*app, init_result_out);
+  MutexLock lock(InstanceIdInternal::mutex());
   if (init_result_out) *init_result_out = kInitResultSuccess;
   auto instance_id = InstanceIdInternal::FindInstanceIdByApp(app);
   if (instance_id) return instance_id;

instance_id/src/desktop/instance_id.cc

@@ -159,6 +159,7 @@ Future<void> InstanceId::DeleteToken(const char* entity, const char* scope) {
 }
 
 InstanceId* InstanceId::GetInstanceId(App* app, InitResult* init_result_out) {
+  MutexLock lock(InstanceIdInternal::mutex());
   if (init_result_out) *init_result_out = kInitResultSuccess;
   auto instance_id = InstanceIdInternal::FindInstanceIdByApp(app);
   if (instance_id) return instance_id;

instance_id/src/instance_id_internal_base.h

@@ -59,6 +59,9 @@ class InstanceIdInternalBase {
   // Find an InstanceId instance associated with an app.
   static InstanceId *FindInstanceIdByApp(App *app);
 
+  // Return the mutex to make sure both find and register are guarded.
+  static Mutex& mutex() { return instance_id_by_app_mutex_; }
+
  private:
   /// Handle calls from Futures that the API returns.
   ReferenceCountedFutureImpl future_api_;

instance_id/src/ios/instance_id.mm

@@ -229,6 +229,7 @@ static void HookAppDelegateMethods(Class clazz) {
 
 InstanceId* InstanceId::GetInstanceId(App* app, InitResult* init_result_out) {
   FIREBASE_ASSERT_MESSAGE_RETURN(nullptr, app, "App must be specified.");
+  MutexLock lock(InstanceIdInternal::mutex());
   if (app != App::GetInstance()) {
     LogError("InstanceId can only be created for the default app on iOS. "
              "App %s is not the default app.", app->name());