1. Ledger was created with ensemble 2 and quorum as 2 and entries were written.
2. While reading entries, 2 BKs out of 3 in cluster were killed and restarted.
3. Client was hung at read call waiting for sync counter notification.
As though I was not able to reproduce this in some tries, but
By looking at the logs and code, following seems to be problem
1. BookieWatcher got the notification first for changes in available bookies.
2. PerChannelBookieClient#disconnect() called from BookieWatcher for failed bookies. This has set the 'this.channel=null;'
3. PerChannelBookieClient#channelDisconnected() call came now, and it proceeded silently without notifying errors to read ops.
So client is hung waiting for result.