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https://issues.apache.org/jira/browse/POOL-396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17364015#comment-17364015
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Phil Steitz commented on POOL-396:
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Nice work on the report and patch. Thanks especially for the unit test
showing the bug. I have a couple of comments on the patch:
# We should remember to apply an analogous patch to GenericKeyedObjectPool,
which is subject to the same issue.
# I think it would be better to fix the eviction state of the object under
test and rethrow the exception (like what borrowObject does when the instance
failing validation has just been created) rather than swallowing the exception
and destroying the instance under test.
When I say "fix the eviction state" I mean basically just call endEvictionTest.
My reasoning for this is that validation exceptions often indicate
infrastructure issues that may be transient and that clients may want to know
about.
> Exceptions in validation can cause an object's lifecycle to be stuck in
> EVICTION state
> --------------------------------------------------------------------------------------
>
> Key: POOL-396
> URL: https://issues.apache.org/jira/browse/POOL-396
> Project: Commons Pool
> Issue Type: Bug
> Affects Versions: 2.4.2, 2.9.0
> Reporter: Jeremy Kong
> Priority: Major
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Currently, if validation of an object throws an exception when testing an
> idle object during eviction, an exception will be thrown from the evict()
> method. This causes the object to be left in the EVICTION state, but still be
> present in the idleObjects queue.
> Future runs of the eviction thread will run into an infinite loop, because
> they pick up the afflicted object from the queue, fail to set its state to
> EVICTION, don't count it as a test, and repeat ad infinitum. This infinite
> loop means that no further evictions will take place; it also causes
> increases in garbage collection owing to allocation of the EvictionIterator
> on each loop iteration.
> This test added to TestGenericObjectPool (plus a small change allowing
> exceptions to be thrown from the validateObject method of SimpleFactory)
> reproduces the issue.
> {code:java}
> @Test
> @Timeout(value = 60000, unit = TimeUnit.MILLISECONDS)
> public void testExceptionInValidationDuringEviction() throws Exception {
> genericObjectPool.setMaxIdle(1);
> genericObjectPool.setMaxTotal(2);
> genericObjectPool.setNumTestsPerEvictionRun(1);
> genericObjectPool.setMinEvictableIdleTime(Duration.ofMillis(0));
> genericObjectPool.setTestWhileIdle(true);
> String active = genericObjectPool.borrowObject();
> genericObjectPool.returnObject(active);
> simpleFactory.setThrowExceptionOnValidate(true);
> try {
> genericObjectPool.evict();
> } catch (Exception e) {
> // OK that a given run fails. But the object should still be evicted.
> }
> genericObjectPool.evict(); // currently fails: causes an infinite loop!
> assertEquals(0, genericObjectPool.getNumActive());
> assertEquals(0, genericObjectPool.getNumIdle());
> }
> {code}
> It seems that protection against exceptions thrown by validation code exist
> elsewhere (e.g. in borrowObject()); similarly, protections against exceptions
> thrown by user eviction policy code exist in evict(). So it looks like the
> testWhileIdle() portion of evict() needs to similarly be protected.
> Thanks!
> Jeremy
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