[jira] [Created] (ARTEMIS-968) Synchronization issue in ActiveMQThreadPoolExecutor

["Erich Duda (JIRA)" <ji...@apache.org>]

Erich Duda created ARTEMIS-968:
----------------------------------

             Summary: Synchronization issue in ActiveMQThreadPoolExecutor
                 Key: ARTEMIS-968
                 URL: https://issues.apache.org/jira/browse/ARTEMIS-968
             Project: ActiveMQ Artemis
          Issue Type: Bug
          Components: Broker
    Affects Versions: 1.5.2, 2.0.0
            Reporter: Erich Duda


During investigation of test failures in Artemis test suite I've noticed that ActiveMQThreadPoolExecutorTest sometimes doesn't allocate new Worker for a task even if {{maxPoolSize = 16}} and there are only 3 tasks to execute. Instead the task is queued and it waits until some worker finishes its job.

I think the problem is in offer method.

{code}
@Override
public boolean offer(Runnable runnable) {
  int poolSize = executor.getPoolSize();

  // If the are less threads than the configured maximum, then the tasks is
  // only queued if there are some idle threads that can run that tasks.
  // We have to add the queue size, since some tasks might just have been queued
  // but not yet taken by an idle thread.
  if (poolSize < executor.getMaximumPoolSize() && (size() + executor.getActive()) >= poolSize)
    return false;

  return super.offer(runnable);
}
{code}

There are 3 variables which are compared with themselves - {{executor.getPoolSize()}}, {{size()}}, {{executor.getActive()}} - without any synchronization. It may happen that the if condition is {{false}} just because some variable hasn't been updated yet.

I've created reproducer \[1\] for this issue. You can run it from branch \[2\] using following commands.

{code}
git clone https://github.com/dudaerich/activemq-artemis
cd activemq-artemis
git checkout ActiveMQThreadPoolExecutorTest

mvn test -Dtest=ActiveMQThreadPoolExecutorTest -Ptests -DfailIfNoTests=false -Drat.ignoreErrors=true 2>&1 | tee log
{code}

\[1\] https://github.com/dudaerich/activemq-artemis/blob/a0eb0ea9caaf22a9d031d480625a638a2e0f300d/tests/unit-tests/src/test/java/org/apache/activemq/artemis/tests/unit/util/ActiveMQThreadPoolExecutorTest.java
\[2\] https://github.com/dudaerich/activemq-artemis/commits/ActiveMQThreadPoolExecutorTest



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