Do I need to treat the below scenario as critical?

I have Android java service which will interact with HAL service using HIDL calls.

I have below scenario, I'm not sure to treat it as critical.

+----------+  (AIDL) +--------------+
|App thread|-------->|Java Service  | (HIDL) +-----------+
+----------+         |(SendFunction)|------->|CPP service|  
                     +--------------+        +-----------+
                     ^
+--------------+     |
|AnotherThread |-----|
+--------------+

Definition of SendFunction is as below.

 private void SendFunction(int status, DiagCommandDesc response) {
      try {
          server.executeCommandResponse(status, response);
         if (Log.isLoggable(TAG, Log.DEBUG)) {
              Log.d(TAG, "Response sent to HAL.");
          }
      } catch (Exception e) {
          if (Log.isLoggable(TAG, Log.DEBUG)) {
             Log.d(TAG, "HAL Server error.");
         }
      }
  }

SendFunction is being called from two different threads. Where server is an instance to CPP Server using HIDL.

MY question.

      server.executeCommandResponse(status, response);

Do I need to treat above call as critical and synchronize it? as server object will be accessed from two different threads.

Solution

No, you do not have to guard the call to server.executeCommandResponse(status, response) in your Java service.

The Binder communication is already thread-safe. That concurrent calls to executeCommandResponse are safe inside the HAL service has to be ensured by the HAL itself. There is an easy way to make it thread-safe on the HAL side: Using a thread-pool with only a single thread. This will make all other threads wait on the first one to finish, though.

int main()
{
    ::android::hardware::configureRpcThreadpool(1, true);
    ::android::sp<MyHal> service = new MyHal;
    if (::android::OK != service->registerAsService())
        return EXIT_FAILURE;
    ::android::hardware::joinRpcThreadpool();
    return EXIT_SUCCESS;
}

You can find more information here: https://source.android.com/devices/architecture/hidl/threading