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https://issues.apache.org/jira/browse/ARTEMIS-968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15869399#comment-15869399
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Erich Duda commented on ARTEMIS-968:
------------------------------------
I searched how to implement ThreadPoolExecutor which would behave like
ActiveMQThreadPoolExecutor on the Internet but I haven't found anything
relevant.
I think it's not possible to do it by extending JDK implementation of
ThreadPoolExecutor, because you don't have access to internal structures and
locks.
I am thinking about modifying of OpenJDK implementation. What do you think? Is
it good idea? Thanks!
> 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
> {{ActiveMQThreadPoolExecutor}} 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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