How many threads per GAE instance?

Does anyone know how many threads does GAE instance (Java, not python) create and under what conditions? The conditions开发者_运维问答 of new instance creation are well described, but there doesn't seem to be any information about how many requests can one multithreaded Java instance serve.

An instance only processes one thread at a time. The first request in the queue is assigned to a free instance as soon as it is created. Once it completes that request, it is free again and another request is assigned to it. One request at a time, per instance.

It is possible that multiple requests are handled concurrently, possibly even on different servers, but within one instance there is only a single thread.