[jira] [Commented] (POOL-231) GOP, GKOP invalidateObject is not threadsafe

["Phil Steitz (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/POOL-231?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13508841#comment-13508841 ] 

Phil Steitz commented on POOL-231:
----------------------------------

Sorry the original test that I included in the description (now edited) was incorrect.  Combining borrow / return loops caused duplicates in the obj array.  I am pretty sure now this is a bug and the description of how it happens is correct.  The test will pass if I patch invalidateObject in GOP to guard destroy(p) using p's monitor and include a second allObjects check:

{code}
 synchronized (p) {
     if (allObjects.get(obj) != null) { 
         destroy(p);
     }
 }
{code}

That is probably not the best way to address the problem (probably better to somehow guard using PooledObject state); but I think it does show that there is a problem and where it is.
                
> GOP, GKOP invalidateObject is not threadsafe
> --------------------------------------------
>
>                 Key: POOL-231
>                 URL: https://issues.apache.org/jira/browse/POOL-231
>             Project: Commons Pool
>          Issue Type: Bug
>    Affects Versions: Nightly Builds
>            Reporter: Phil Steitz
>             Fix For: 2.0
>
>
> There does not appear to be sufficient sync protection for the destroyCount and createCount counters when destroy is activated by invalidateObject in GOP, GKOP, v2 trunk.  The test below fails when added to GOP tests. The destroyCount is over-incremented due (I think) to the fact that multiple threads can enter destroy before the object being invalidated is removed from allObjects.  This problem was originally reported by Thomas Neidhart in a comment on POOL-213.
> {code}
> @Test
>     public void testConcurrentInvalidate() throws Exception {
>         // Get allObjects and idleObjects loaded with some instances
>         final int nObjects = 1000;
>         pool.setMaxTotal(nObjects);
>         pool.setMaxIdle(nObjects);
>         final Object[] obj = new Object[nObjects];
>         for (int i = 0; i < nObjects; i++) {
>             obj[i] = pool.borrowObject();
>         }
>         for (int i = 0; i < nObjects; i++) {
>             if (i % 2 == 0) {
>                 pool.returnObject(obj[i]);
>             }
>         }
>         final int nThreads = 100;
>         final int nIterations = 100;
>         final InvalidateThread[] threads = new InvalidateThread[nThreads];
>         // Randomly generated list of distinct invalidation targets
>         final ArrayList<Integer> targets = new ArrayList<Integer>();
>         final Random random = new Random();
>         for (int j = 0; j < nIterations; j++) {
>             // Get a new invalidation target
>             Integer targ = new Integer(random.nextInt(nObjects));
>             while (targets.contains(targ)) {
>                 targ = new Integer(random.nextInt(nObjects));
>             }
>             targets.add(targ);
>             // Launch nThreads threads all trying to invalidate the target
>             for (int i = 0; i < nThreads; i++) {
>                 threads[i] = new InvalidateThread(pool, obj[targ]);
>             }
>             for (int i = 0; i < nThreads; i++) {
>                 new Thread(threads[i]).start();
>             }
>             boolean done = false;
>             while (!done) {
>                 done = true;
>                 for (int i = 0; i < nThreads; i++) {
>                     done = done && threads[i].complete();
>                 }
>                 Thread.sleep(100);
>             }
>         }
>         Assert.assertEquals(nIterations, pool.getDestroyedCount());
>     }
>     
>     static class InvalidateThread implements Runnable {
>         final private Object obj;
>         final private ObjectPool<Object> pool;
>         private boolean done = false;
>         public InvalidateThread(ObjectPool<Object> pool, Object obj) {
>             this.obj = obj;
>             this.pool = pool;
>         }
>         public void run() {
>             try {
>                 pool.invalidateObject(obj);
>             } catch (IllegalStateException ex) {
>                 // Ignore
>             } catch (Exception ex) {
>                 Assert.fail("Unexpected exception " + ex.toString());
>             } finally {
>                 done = true;
>             }
>         }
>         public boolean complete() {
>             return done;
>         }
>     }
> {code}

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