People sometimes run to complicated systems, when right before you there is a solution. In this case, it is with the filesystem itself.
It turns out mkdir is an atomic event (at least on filesystems I've encountered). And, from that simple thing, you can build something reasonable as long as you do not need high performance. and space isn't an issue. You need a 2 layer lock (make 2 directories) and you need to keep 2 data files around plus a 3rd temporary file. The reader reads from the newest of the 2 data files. The writer makes the locks, deletes the oldest data file and renames it's temporary file to be the new data file. You could have the locks expire after 10 minutes, to take care of failure to clean up. Ultimately, the writer is responsible for keeping the locks alive. The writer knows it is his lock because it has his timestamp. If the writer dies, no big deal, since it only affected a temporary file and the locks will expire. Rename the temporary file takes advantage of the fact that a rename is essentially immediate. Since, whatever does the reading, only reads from the newest of the 2 files (if both are available). Once, the rename of the temporary file done by the writer is complete, any future reads will now hit the newest data. And, deleting the oldest file doesn't matter since the reader never looks at it. If you want more specifics let me know. john -- http://mail.python.org/mailman/listinfo/python-list
