Bug 54906

Summary:	WebappClassLoader.loadedByThisOrChild can throw ConcurrentModificationException
Product:	Tomcat 8	Reporter:	Nate Clark <apache>
Component:	Catalina	Assignee:	Tomcat Developers Mailing List <dev>
Status:	RESOLVED FIXED
Severity:	enhancement
Priority:	P2
Version:	8.0.x-trunk
Target Milestone:	----
Hardware:	PC
OS:	Linux
Attachments:	Patch to catch ConcurrentModificationException while iterating over a collection

Description Nate Clark 2013-04-29 19:25:04 UTC

Created attachment 30240 [details]
Patch to catch ConcurrentModificationException while iterating over a collection

This is related to bug 54497. A common exception seen in 7.0.33 during stop is a ConcurrentModification in loadedByThisOrChild.

java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to stop component [StandardEngine[Tomcat].StandardHost[localhost].StandardContext[/mobile/login/oauth]]
	at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:252)
	at java.util.concurrent.FutureTask.get(FutureTask.java:111)
	at org.apache.catalina.core.ContainerBase.stopInternal(ContainerBase.java:1179)
	at org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)
	at org.apache.catalina.core.ContainerBase$StopChild.call(ContainerBase.java:1575)
	at org.apache.catalina.core.ContainerBase$StopChild.call(ContainerBase.java:1564)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.catalina.LifecycleException: Failed to stop component [StandardEngine[Tomcat].StandardHost[localhost].StandardContext[/mobile/login/oauth]]
	at org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:236)
	... 7 more
Caused by: org.apache.catalina.LifecycleException: Failed to stop component [WebappLoader[/mobile/login/oauth]]
	at org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:236)
	at org.apache.catalina.core.StandardContext.stopInternal(StandardContext.java:5521)
	at org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)
	... 7 more
Caused by: java.util.ConcurrentModificationException
	at java.util.Vector$Itr.checkForComodification(Vector.java:1156)
	at java.util.Vector$Itr.next(Vector.java:1133)
	at org.apache.catalina.loader.WebappClassLoader.loadedByThisOrChild(WebappClassLoader.java:2599)
	at org.apache.catalina.loader.WebappClassLoader.checkThreadLocalMapForLeaks(WebappClassLoader.java:2515)
	at org.apache.catalina.loader.WebappClassLoader.checkThreadLocalsForLeaks(WebappClassLoader.java:2455)
	at org.apache.catalina.loader.WebappClassLoader.clearReferences(WebappClassLoader.java:1996)
	at org.apache.catalina.loader.WebappClassLoader.stop(WebappClassLoader.java:1902)
	at org.apache.catalina.loader.WebappLoader.stopInternal(WebappLoader.java:661)
	at org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)
	... 9 more

The fix for 54497 stops the exception from failing the stop but it still fails the rest of the ThreadLocal leak check. It would be better if ConcurrentModificationException was caught in loadedByThisOrChild and only that one check fails.

Comment 1 Mark Thomas 2013-05-04 21:54:21 UTC

loadedByThisOrChild() is called by more than just the thread load code so I used your patch but with a dedicated error message rather than re-using an existing one.

The fix has been applied to trunk and 7.0.x and will be included in 7.0.40 onwards.