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This feature is pretty similar to how Squid actually implements Collapsed Forwarding. When ATS goes to fetch something from cacheorigin, and upon receiving the response from origin, any number of clients can be allowed to start serving out of the partially filled cache object. The difference (Ed: I think?) is that Squid allows this as soon as we go it goes to origin, whereas ATS can not do it until we get the complete response header. The reason for this is that we make no distinction between cache refresh, and cold cache, so we have no way to know if a response is going to be cacheable, and therefore allow read-while-write functionality.

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