[SOLR-7401] NPE when concurrently creating and deleting collections

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 5.2, 6.0
• Component/s: SolrCloud
• Assignee: Shai Erera
• Reporter: Shai Erera
• Created: 15/Apr/15 13:15
• Updated: 09/May/16 18:45
• Resolved: 15/Apr/15 15:23

Description

I've hit this when multiple tests run against the same Solr server. Some tests create a collection, do some stuff and then delete it, but there are two tests which create+delete a collection, and then assert it doesn't exist by searching it (expecting to hit an exception). While I think this isn't the best way to assert a collection doesn't exist (I intend to change this assert to use a LIST command), it did surface this concurrency bug.

java.lang.NullPointerException
	at java.util.ArrayList.addAll(ArrayList.java:577)
	at org.apache.solr.servlet.SolrDispatchFilter.getSlicesForCollections(SolrDispatchFilter.java:731)
	at org.apache.solr.servlet.SolrDispatchFilter.getRemotCoreUrl(SolrDispatchFilter.java:669)

The problem is that getSlicesForCollections may get a CollectionRef whose collection value may be null, therefore attempting to add null to the list. I reproduced in a test, and fixed the bug.