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From Justin Erenkrantz <jus...@erenkrantz.com>
Subject Re: mod_cache
Date Mon, 07 Mar 2005 05:06:26 GMT
--On Sunday, March 6, 2005 1:54 PM +0100 Sander Striker <striker@apache.org> 
wrote:

> I completely agree.  So much even that I just committed it (r156306).
> Why are we storing the header fd in the disk object anyways?  I haven't
> gone through mod_disk_cache.c yet, but at least for store_headers() it
> doesn't seem to make any sense.

It's not really the 'disk' object per se - it's part of mod_disk_cache's 
private cache handle.  When we open the cache handle, we also open the 
associated file descriptors in open_entity to ensure that we have something 
valid cached.  We then use those open descriptors in recall_headers and 
recall_body later on.

Note that we're a little tricky and we partially read the header file in 
open_entity to get some meta-data via file_cache_recall_mydata, but we hold 
off parsing the full MIME headers from disk until recall_headers time.

> When it comes to store_headers(), shouldn't that be done using a temp
> file and moving it into place atomically just like store_body?  Are
> we relying on OS buffering and header size being small enough to pull
> that off?  Or am I just being paranoid? :)

Yes, there's probably a race condition here.  However, store_headers is only 
called once, so the window is relatively small compared to store_body which 
can be called multiple times.  Feel free to have at it.  ;-)  -- justin

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