flock: "it waits indefinitely until the lock is granted"

I don't know of an easy to do what you want without polling. From the looks of it though, your locks are really short lived, so it should not be a problem.

Update: s/should be/should not be/

In reply to Re^3: file reading / writing collisions by ikegami
in thread file reading / writing collisions by simonodell

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