Re: Findbugs and locks?

Jeff Higgins <>
Thu, 31 Jul 2008 07:14:05 -0400
Knute Johnson wrote:

Daniel Pitts wrote:

Knute Johnson wrote:

Ah but look at what does!

  static void method(int n) throws IOException {

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

I think it is a bug in findbugs. I think I'll drop them a line.

I don't think its a bug in findbugs.
The problem is that lockArray[n] might through an exception in the
finally if the lockArray changes size. lockArray[n] might also be
assigned a null at some point, so lockArray[n].writeLock() could
through an NPE.

I think a better approach would be to have method take a Lock rather
than an index into an array.

Hope this helps,

If the lock throws an exception, how can it be locked?

After a night's rest, I think that:
ReentrantReadWriteLock.writeLock() is a factory method.

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

public class SSCCE {

   ReentrantReadWriteLock reentrantLock =
     new ReentrantReadWriteLock();

   void methodA() {

     // FindBugs Eclipse WinXP
     //produces no bug report
     WriteLock lock = reentrantLock.writeLock();
     try {
       // do some disk I/O
     } finally {
    // Here we have a reference to _lock_ WriteLock.

   void methodB() {

     // FindBugs Eclipse WinXP produces:
     // [UL] Method does not release lock on all exception paths
     // on the following line
     try {
         // do some disk I/O
     } finally {
       // Here we unlock _any_ WriteLock that
       // ReentrantReadWriteLock.writeLock() constructs.

   public static void main(String[] args) {}

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