[jboss-jira] [JBoss JIRA] Commented: (JGRP-1190) Race conditions in logical address caching with shared transport

Race conditions in logical address caching with shared transport ---------------------------------------------------------------- Key: JGRP-1190 URL: https://jira.jboss.org/jira/browse/JGRP-1190 Project: JGroups Issue Type: Bug Reporter: Brian Stansberry Assignee: Bela Ban Fix For: 2.10 Attachments: JGRP-1190.patch, ns.patch The logical address caching (i.e. TP.logical_addr_cache) is prone to races when the shared transport is used. JBoss AS's startup simultaneously connects 2 channels on a shared transport. With 2.10.0-Alpha3 we're seeing problems with addresses for still healthy members being removed from logical_addr_cache. An entry is added to the cache when: 1) an event comes down the stack, i.e. from Channel.setAddress(). 2) A Discovery GET_MBRS_REQ comes in, either from a remote node or from receipt of the nodes own message. Primary mechanism for marking an entry for removal is a VIEW_CHANGE event comes down the stack, which results in a retainAll() invocation on the cache; only addresses that are part of the views of the channels associated with the shared TP are retained. This can lead to the following kind of race where C1 and C2 are 2 channels sharing the TP, ADD is one the events described above that adds to the cache, and VIEW is a VIEW_CHANGE event coming down: 1) C1:ADD 2) C2:ADD 3) C1:VIEW --- oops -- whatever C2:ADD added is marked as removable 4) C2:VIEW Besides this larger issue, there is also a minor race in TP.handleDownEvent's handling of address caches when there is a view change: case Event.VIEW_CHANGE: synchronized(members) { View view=(View)evt.getArg(); members.clear(); if(!isSingleton()) { Vector<Address> tmpvec=view.getMembers(); members.addAll(tmpvec); } else { // add all members from all clusters for(Protocol prot: up_prots.values()) { if(prot instanceof ProtocolAdapter) { ProtocolAdapter ad=(ProtocolAdapter)prot; Set<Address> tmp=ad.getMembers(); members.addAll(tmp); } } } } // fix for https://jira.jboss.org/jira/browse/JGRP-918 logical_addr_cache.retainAll(members); UUID.retainAll(members); break; The two retainAll calls at the end need to be inside the synchronized block. Otherwise if TP is a shared transport, two threads can simultaneously be carrying down view changes. T1 proceeds through the synchronized block. Then while it is updating the address caches, T2 enters the sync block and begins manipulating 'members' with the result that the data passed by T1 to retainAll is incomplete.