Lifetime of Thread object?

Does anyone have a good description of how long a given Thread lives in the context of a request to a RoR application? Specifically:

- Do I know that a given request only uses one Thread? (unless I explicitly fork another one in my code)

- Do I know that a given Thread only lasts for one request?

- If I cram some data into Thread.current early-on in processing the request, do I know that this data will be available to objects later in the request, and the data won't be available to (or overwritten by) another request?