Bug 1017673 – ConcurrentModificationException in TimerService.getTimers()

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Bug 1017673 - ConcurrentModificationException in TimerService.getTimers()

Summary:	ConcurrentModificationException in TimerService.getTimers()

Status:	CLOSED CURRENTRELEASE

Aliases:	None

Product:	JBoss Enterprise Application Platform 6
Classification:	JBoss
Component:	EJB (Show other bugs)
Sub Component:
Version:	6.2.0
Hardware:	Unspecified Unspecified

Priority	unspecified Severity medium
Target Milestone:	DR0
Target Release:	EAP 6.3.0
Assigned To:	Jan Martiska
QA Contact:	Jan Martiska
Docs Contact:	Russell Dickenson

URL:
Whiteboard:
Keywords:

Depends On:
Blocks:
	Show dependency tree / graph

Reported:	2013-10-10 06:20 EDT by Jan Martiska
Modified:	2014-06-28 11:44 EDT (History)
CC List:	4 users (show)

See Also:
Fixed In Version:
Doc Type:	Bug Fix
Doc Text:	If a bean attempted to create a new timer at the same time as another thread was calling the `getTimers()` method, a `ConcurrentModificationException` was thrown. This occurred because the `getTimers()` method did not call `synchronized()` on the timers. This issue is fixed in this release, and the timer service implementation's `getTimers()` method now properly calls `synchronized()` on the timers.
Story Points:	---
Clone Of:
Environment:
Last Closed:	2014-06-28 11:44:52 EDT
Type:	Bug
Regression:	---
Mount Type:	---
Documentation:	---
CRM:
Verified Versions:
Category:	---
oVirt Team:	---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---

Attachments	(Terms of Use)
reproducer (3.03 KB, application/zip) 2013-10-10 06:20 EDT, Jan Martiska	no flags	Details
Add an attachment (proposed patch, testcase, etc.)

Groups: None (edit)

Description Jan Martiska 2013-10-10 06:20:46 EDT

Created attachment 810437 [details]
reproducer

The implementation of org.jboss.as.ejb3.timerservice.TimerService.getTimers() iterates over three collections (activePersistentTimers, persistentWaitingOnTxCompletionTimers, nonPersistentTimers) using a for-each loop without synchronizing on them.
This can lead to a ConcurrentModificationException if a bean is creating a timer and at the same time another thread is calling getTimers().

Reproducer mimicking this scenario is attached. Just deploy it to a running EAP instance. A Singleton bean will create/remove lots of timers and at the same time another thread will call getTimers repeatedly.

Expected outcome: it deploys successfully and says "No ConcurrentModificationException encountered"

Actual outcome - after some time: 
java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894) [rt.jar:1.7.0_25]
	at java.util.HashMap$ValueIterator.next(HashMap.java:922) [rt.jar:1.7.0_25]
	at org.jboss.as.ejb3.timerservice.TimerServiceImpl.getTimers(TimerServiceImpl.java:372)
	at TimerGenerator.getTimers(TimerGenerator.java:63)	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.7.0_25]
(....)

Comment 2 Dimitris Andreadis 2013-10-24 14:28:05 EDT

Assigning jpai@redhat.com EJB issues to david.lloyd@redhat.com. Please re-assign to Cheng or others as needed.

Comment 3 Jan Martiska 2013-10-30 09:18:15 EDT

Going to fix this myself.

Comment 4 Jan Martiska 2013-11-06 05:29:22 EST

Can't reproduce on upstream, it seems it was fixed there earlier with commit 7a4541f6.

Comment 8 David M. Lloyd 2014-01-02 10:08:56 EST

The pull request looks OK so I'm devel_ack+ this.

Comment 9 Jan Martiska 2014-02-12 05:23:40 EST

Fixed in 6.3.0.DR0.

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