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    <p>What you're looking for is a lock upgrade, and is not possible (at least not atomically) using the standard java.concurrent ReentrantReadWriteLock. Your best shot is unlock/lock, and then check that noone made modifications inbetween.</p> <p>What you're attempting to do, forcing all read locks out of the way is not a very good idea. Read locks are there for a reason, that you shouldn't write. :)</p> <p><b>EDIT:</b><br> As Ran Biron pointed out, if your problem is starvation (read locks are being set and released all the time, never dropping to zero) you could try using fair queueing. But your question didn't sound like this was your problem?</p> <p><b>EDIT 2:</b><br> I now see your problem, you've actually acquired multiple read-locks on the stack, and you'd like to convert them to a write-lock (upgrade). This is in fact impossible with the JDK-implementation, as it doesn't keep track of the owners of the read-lock. There could be others holding read-locks that you wouldn't see, and it has no idea how many of the read-locks belong to your thread, not to mention your current call-stack (i.e. your loop is killing <em>all</em> read locks, not just your own, so your write lock won't wait for any concurrent readers to finish, and you'll end up with a mess on your hands)</p> <p>I've actually had a similar problem, and I ended up writing my own lock keeping track of who's got what read-locks and upgrading these to write-locks. Although this was also a Copy-on-Write kind of read/write lock (allowing one writer along the readers), so it was a little different still.</p>
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    1. POJava ReentrantReadWriteLocks - how to safely acquire write lock?
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    1. CORight, that's the issue. I'm not trying to force ALL read locks out of the way, just the ones held by the current thread. I'm happy for the write lock acquisition to wait for *other* threads to release their read locks.
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    2. COIn fact the JDK implementation does keep track of who locked the readlock to some extent; getReadHoldCount() returns the count for the current thread only (via a ThreadLocal) so exactly the right number of unlocks() can be called in this situation. The code I put in my own answer does in fact work.
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    3. COinteresting, then this has been changed in jdk1.6, jdk1.5 does not use thread locals at all.
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