Sagar Miglani created SLING-11620:
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Summary: Synchronization issue in Webconsole Security Provider
Key: SLING-11620
URL: https://issues.apache.org/jira/browse/SLING-11620
Project: Sling
Issue Type: Bug
Components: Extensions
Affects Versions: Web Console Security Provider 1.2.6
Reporter: Sagar Miglani
Attachments: BlockedThreads.png, WebconsoleServiceListeners.patch
WebconsoleSecurityProvider's
[ServiceListeners|https://github.com/apache/sling-org-apache-sling-extensions-webconsolesecurityprovider/blob/master/src/main/java/org/apache/sling/extensions/webconsolesecurityprovider/internal/ServicesListener.java]
class has three fields of Listener (an inner class of {{ServiceListeners}}
implementing {{ServiceListener}}) {{repositoryListener}},
{{authSupportListener}}, {{authListener}}.
Each of listener uses synchronized methods and on any {{ServiceChanged}} event
it may call {{notifyChange}} method of {{ServiceListeners}} parent class which
is also a synchronized method and in this method we are again calling all of
the listener fields' {{getService}} sychronized methods
If two service events for these listeneres fields occur simulatenously a
deadlock situation may arise.
eg:
Thread1:
- repositoryListener -> serviceChanged
- synchronized retainSerivce - (self lock acquired)
- synchronized notifyChange - (parent's lock acquired)
Thread2:
- authSupportListener -> serviceChanged
- synchronized retainService - (self lock aquired)
- synchronized notifyChange - (wait for thread 1 to release parent's lock)
Thread1:
- synchronized (authSupportListener) getService - (wait for thread 2 to
release the lock)
Tried to replicate the scenario [^WebconsoleServiceListeners.patch]. The test
in this patch file fails due to timeout.
On taking thread snapshot you may see the thread blocked and waiting for each
other. [^BlockedThreads.png]
Shouldn't these all listener fields and parent class be using the shared lock
instead of sychronized methods
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