meter specifying whether request should
wait until lock is available or fail if lock can not be granted immediately.
<DT><B>Returns</B>
<DL>
<DT><code>true</code> if lock is successfully granted<br>
<DT><code>false</code> if lock can not be granted within specified time 
</DL></DL></DL></A>

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<A NAME = "Persistent.unlock">
<B>unlock()</B>
<DL><DD>
Remove granted lock. If lock was requested several times by one thread, then correspondent number of unlocks is needed to release the lock.
</DL></A>

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