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Posted to dev@tomcat.apache.org by GitBox <gi...@apache.org> on 2022/05/18 13:49:10 UTC
[GitHub] [tomcat] aooohan opened a new pull request, #515: Bug:Deadlocks occur when both engine and host startStopThreads values are set and the latter value is larger than the former
aooohan opened a new pull request, #515:
URL: https://github.com/apache/tomcat/pull/515
# Reproduce
```xml
<Engine name="Catalina" defaultHost="localhost" startStopThreads="3">
<Host name="localhost" appBase="webapps"
unpackWARs="true" autoDeploy="true" startStopThreads="4">
</Host>
</Engine>
```
**When starting tomcat as configured above, the situation shown in the image below will occur.**
<img width="1669" alt="image" src="https://user-images.githubusercontent.com/40265686/169047128-b7fefd31-7a1a-4ba4-96e7-05dfbd2156dc.png">
**been stuck here**⬆️⬆️⬆️
**Then i used the Arthas tool to look at the threads and the results are shown below.**
<img width="1709" alt="image" src="https://user-images.githubusercontent.com/40265686/169047640-8c2d689d-3e23-49c4-861b-b1c5a4d6ce3e.png">
<img width="1350" alt="image" src="https://user-images.githubusercontent.com/40265686/169047710-d9d8e8a9-c2f0-41ff-92dc-148d9d99a52c.png">
<img width="1509" alt="image" src="https://user-images.githubusercontent.com/40265686/169048027-9b1c1e43-8ccc-4782-b9ed-cbf2d518dcf6.png">
When starting tomcat, the current StandardServer instance object has been locked in LifecycleBase#start. When we do not set the startStopThreads value of StandardEngine, startStopThreads defaults to 1. At this time, startStopExecutor in StandardEngine is actually an instance of InlineExecutorService (in fact, the current thread), so when StandardEngine starts its subcontainer StandardHost through the startStopExecutor thread pool, because it is the current thread, there is no problem when executing the .StandardServer#reconfigureUtilityExecutor method.
However, when the startStopExecutor in StandardEngine is not InlineExecutorService (ie Server#getUtilityExecutor()), the StandardServer#reconfigureUtilityExecutor method is executed again（The host's startStopThreads value is greater than the engine's startStopThreads）, because the lock of the StandardServer instance has not been released at this time, resulting in a deadlock.
> My English is limited, I don't know if I have explained it clearly, or I am thinking in the wrong direction
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[GitHub] [tomcat] rmaucher closed pull request #515: Bug:Deadlocks occur when both engine and host startStopThreads values are set and the latter value is larger than the former
Posted by GitBox <gi...@apache.org>.
rmaucher closed pull request #515: Bug:Deadlocks occur when both engine and host startStopThreads values are set and the latter value is larger than the former
URL: https://github.com/apache/tomcat/pull/515
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[GitHub] [tomcat] rmaucher commented on pull request #515: Bug:Deadlocks occur when both engine and host startStopThreads values are set and the latter value is larger than the former
Posted by GitBox <gi...@apache.org>.
rmaucher commented on PR #515:
URL: https://github.com/apache/tomcat/pull/515#issuecomment-1131604290
Thanks a lot for your PR. Sorry, I forgot to close it after merging it manually. The fix will be in Tomcat 10.1.0-M16, 10.0.22, 9.0.64. Tomcat 8.5 is not affected since it doesn't have the utility executor feature.
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[GitHub] [tomcat] rmaucher commented on pull request #515: Bug:Deadlocks occur when both engine and host startStopThreads values are set and the latter value is larger than the former
Posted by GitBox <gi...@apache.org>.
rmaucher commented on PR #515:
URL: https://github.com/apache/tomcat/pull/515#issuecomment-1131378209
Good idea, the sync is overloaded in that case so this is risky, and other operations already use a servicesLock item for this reason.
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[GitHub] [tomcat] aooohan commented on pull request #515: Bug:Deadlocks occur when both engine and host startStopThreads values are set and the latter value is larger than the former
Posted by GitBox <gi...@apache.org>.
aooohan commented on PR #515:
URL: https://github.com/apache/tomcat/pull/515#issuecomment-1131597904
@rmaucher Thank u for reviewing my PR, it's an honour to contribute PR to Tomcat.
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