[jira] [Created] (SLING-11620) Synchronization issue in Webconsole Security Provider

["Sagar Miglani (Jira)" <ji...@apache.org>]

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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