Re: Findbugs and locks?

From:
Lew <com.lewscanon@lew>
Newsgroups:
comp.lang.java.help
Date:
Wed, 30 Jul 2008 09:17:03 -0400
Message-ID:
<W8idnb6wlL1N9A3VnZ2dnUVZ_hydnZ2d@comcast.com>
Jeff Higgins wrote:

    if (n < lockArray.length) {
      ReentrantReadWriteLock rrwl = lockArray[n];
      WriteLock lock = rrwl.writeLock();
      try {
        lock.lock();
        // do some disk I/O
      } finally {
        lock.unlock();
      }
    }
  }


Is there a chance that lock.lock() would fail?

If so, would lock.unlock() cause any harm?

The usual pattern for resource acquisition and release with try-finally is

  resource.acquire();
  // break flow on acquire() failure
  try
  {
    ...
  }
  finally
  {
   resource.release();
  }

That way the release() only occurs if the acquire() succeeds. Moving the
acquire() into the try{} means that the release() will occur even if acquire()
fails. This is how Knute coded it, and I don't see why his way caused a warning.

I would be more comfortable if Knute's way didn't cause any warnings, because
I don't understand it either. However, I'm unfamiliar with Findbugs (although
many recommend it very highly).

--
Lew

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