Github user hanm commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/92#discussion_r97451281
  
    --- Diff: 
src/java/main/org/apache/zookeeper/server/quorum/QuorumCnxManager.java ---
    @@ -468,31 +469,33 @@ synchronized private boolean connectOne(long sid, 
InetSocketAddress electionAddr
          */
         
         synchronized void connectOne(long sid){
    +        connectOne(sid, self.getLastSeenQuorumVerifier());
    +    }
    +
    +    synchronized void connectOne(long sid, QuorumVerifier lastSeenQV){
             if (senderWorkerMap.get(sid) != null) {
    -             LOG.debug("There is a connection already for server " + sid);
    -             return;
    +            LOG.debug("There is a connection already for server " + sid);
    +            return;
             }
    -        synchronized(self) {
    -           boolean knownId = false;
    -            // Resolve hostname for the remote server before attempting to
    -            // connect in case the underlying ip address has changed.
    -            self.recreateSocketAddresses(sid);
    -            if (self.getView().containsKey(sid)) {
    -               knownId = true;
    -                if (connectOne(sid, self.getView().get(sid).electionAddr))
    -                   return;
    -            } 
    -            if (self.getLastSeenQuorumVerifier()!=null && 
self.getLastSeenQuorumVerifier().getAllMembers().containsKey(sid)
    -                   && (!knownId || 
(self.getLastSeenQuorumVerifier().getAllMembers().get(sid).electionAddr !=
    -                   self.getView().get(sid).electionAddr))) {
    -               knownId = true;
    -                if (connectOne(sid, 
self.getLastSeenQuorumVerifier().getAllMembers().get(sid).electionAddr))
    -                   return;
    -            } 
    -            if (!knownId) {
    -                LOG.warn("Invalid server id: " + sid);
    +        boolean knownId = false;
    +        // Resolve hostname for the remote server before attempting to
    +        // connect in case the underlying ip address has changed.
    +        self.recreateSocketAddresses(sid);
    +        if (self.getView().containsKey(sid)) {
    --- End diff --
    
    @shralex Thanks for review comments! Made two changes:
    
    * Refactored the code to reuse getView results. This view is not passed in 
as I thought that's simplified caller site.
    * This code block inside connectOne is now synchronized with the same lock 
that protecting other view / quorum verifiers of the same QuorumPeer. I think 
this makes the code block semantically equivalent to the previous code block 
before this change, where the code block was synchronizing on the whole 
QuorumPeer 'self' with the intention that during the entire execution of 
connectOne, accesses to configs are protected. I did not add any comments as 
with the explicit synchronizing block, the semantic should be self explanatory. 
    
    My stress tests look good so far with latest changes.



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