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From "Philip A. Prindeville" <phil...@enteka.com>
Subject Naive question about mod_proxy
Date Fri, 15 Aug 1997 00:25:39 GMT
I was just wondering, without having scrutinized the source, what
happens if two requests come in for the same URL and overlap?  That
is, a request comes in for a URL, the server starts to download it
via a proxy connection, and then a second request comes in to get it
before the first completes...

How is cache consistency guaranteed?  I'm supposing that no entry is
put into the cache until the download is completed, so the second
request will cause a second download to happen...  Now when the second
transfer completes, will he check again to ensure nothing will be
overwritten in the cache?

If a marker were put into the cache, like "in progress" when the first
request happened, then a second (unnecessary) transfer could be
avoided.  But then, how would one httpd signal the other httpd that
the entry is in the cache and he can reply to the request?

You could use shared memory and semaphores, but that is kind of ugly...
And both processes would block on a single transfer, which is sub-
optimal.

-Philip

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