Is IBinder.transact() thread-safe?

Question

Context to the problem:
I am creating a client that binds to a service that uses a custom RPC (i.e. it doesn't user Messenger or AIDL). So, I need to interact directly with a IBinder calling transact. From reading the documentation, transact is synchronous and, in my case, the call takes a couple hundred milliseconds. So to not block the main thread, I created a thread pool and execute it using the thread pool. However, going through the aforementioned documentation, I couldn't find anywhere that stated if the transact method is thread safe.

Question: can transact be called by multiple threads or do I have to guard it with a synchronize block?

I am aware that Binder.onTransact can be called (by the os) by multiple threads but that doesn't say anything about transact.