GAE: How to share context between threads and/or instances
Assuming your application is running on GAE Standard:

In theory there may be ways to share state between threads that run on the same instance. In Python, this could take the form of a module level variable. This might make sense for extremely specialized types of caching, but it isn't reliable or durable because instances come and go over time. It also introduces the idea of cold and warm instances, which will make performance metrics harder to interpret.
There is not a way to share state between instances without using another system like Memcache or Datastore. It may seem like overkill for a small dataset, but those tools are probably what you're looking for.
I'm wondering if there's a way how to share context between individual:

threads
instances

on Google App Engine. I assume memcache would do the job, but in my case the context is just a single integer and memcache sounds like an overkill.