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Cyrus IMAP File Locking

File Locking in Cyrus IMAP

In order to guard against deadlocks, we want to maintain the same order of acquiring locks throughout the system (this may be violated in one or two places, but when it is it is commented as to why it is safe). As long as everyone plays by these rules, we can avoid deadlock.

In an ideal world, our locking order is:

cyrus.header
cyrus.index
quota
seen
mailboxes file

These try to go from least general to most general, so we hold the largest locks for the shortest period of time.