[Spambayes] question about .procmailrc

[galili assaf]

Hello all,
I have a question about .procmailrc and not spambayes, but maybe someone can assist me.
I want to synchronize a part in .procmailrc.
This is what I am doing: in .promailrc I am executing a java call which modify a csv file.
If two mails a accepted almost the same time, sometimes there is a write-write problem, and only one execution will modify the file.
therefore I would like to synchronize the calls to the java executions.
How can I do a lock?
Thank you very much,
Asaf