Brian Candler wrote:
On Thu, Jan 09, 2003 at 02:54:34PM +0100, Xavier Beaudouin wrote:

Le jeudi, 9 jan 2003, � 14:10 Europe/Paris, Sam Varshavchik a �crit :


[... snip ...]

solaris... With about > 600 000 users, so I may be don't know what I am talking about...

Look at the code for handling the cache file.

1. It opens and reads the courierpop3dsizelist file (if any)

2. For all files which are in the mailbox but not in the cache, it works
   out the size as before. For all files which are in the cache but not in
   the directory listing, they are forgotten about.

3. It then writes the updated cache to a temporary file and then does an
   atomic rename to 'courierpop3dsizelist'. At all instants the file is
   complete and valid. There is no need to lock the file. There is no
   race condition.
To move the temporary file, you need to delete the current courierpop3dsizelist before.
In this case, what is happen if another pop3d process try to access between the delete and the move.

The file is never modified, only replaced in its entirety. That's what makes
it safe.

Regards,

Brian.


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