Phil Steitz created POOL-386:
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Summary: Closing a pool can cause Evictor in another pool to be
cancelled
Key: POOL-386
URL: https://issues.apache.org/jira/browse/POOL-386
Project: Commons Pool
Issue Type: Task
Affects Versions: 2.8.0, 2.7.0, 2.6.2, 2.6.1
Reporter: Phil Steitz
Fix For: 2.8.1
The fix for POOL-337 introduced a race condition that can cause the shared
EvictionTimer to be cancelled when a pool is closed but another pool still has
an active Evictor. The EvictionTimer cancel method used to cancel an eviction
task owned by a client pool uses this test to determine whether or not to
shutdown its executor:
{code:java}
if (executor != null && executor.getQueue().isEmpty()){code}
The executor may report an empty queue if it is executing a task. This will
cause the executor to be shut down and scheduling of new tasks to stop.
The unit test below illustrates the problem.
{code:java}
public void testEvictionTimerMultiplePools() throws InterruptedException {
final AtomicIntegerFactory factory = new AtomicIntegerFactory();
factory.setValidateLatency(50);
final GenericObjectPool<AtomicInteger> evictingPool = new
GenericObjectPool<>(factory);
evictingPool.setTimeBetweenEvictionRunsMillis(100);
evictingPool.setNumTestsPerEvictionRun(5);
evictingPool.setTestWhileIdle(true);
evictingPool.setMinEvictableIdleTimeMillis(50);
for (int i = 0; i < 10; i++) {
try {
evictingPool.addObject();
} catch (Exception e) {
e.printStackTrace();
}
}
for (int i = 0; i < 1000; i++) {
GenericObjectPool<AtomicInteger> nonEvictingPool = new
GenericObjectPool<>(factory);
nonEvictingPool.close();
}
Thread.sleep(1000);
Assert.assertEquals(0, evictingPool.getNumIdle());
evictingPool.close();
}
{code}
Proposed fix:
Change the test guarding executor shutdown to
{code:java}
executor.getQueue().isEmpty() && executor.getActiveCount() == 0
{code}
This still exposes a low-probability race - a task completes after the isEmpty
test and is requeued before the activecount test - but this is very unlikely.
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