RetransmitTask throws NPE ------------------------- Key: JGRP-1567 URL: https://issues.jboss.org/browse/JGRP-1567 Project: JGroups Issue Type: Bug Affects Versions: 3.2.6 Reporter: Radim Vansa Assignee: Bela Ban Fix For: 3.2.7, 3.3 After the UNICAST2.STABLE message is received, {{sent_msgs.purge()}} is called for the sender's entry and Table's {{low == hd == hr}}. Then the {{SenderEntry.getFirstMessage()}} returns null and that causes the NPE below. There is another race condition when this may happen: When the message is sent down the stack for a new destination a {{SenderEntry}} is inserted into {{send_table}}. This entry, however, contains no messages yet, and, therefore, as the RetransmitTask in {{triggerXmit}} retrieves the first message, it gets null and throws NPE. {code} 08:19:05,716 ERROR [org.jgroups.util.TimeScheduler2] (Timer-2,edg-perf09-2672) failed running task UNICAST2: RetransmitTask (interval=500 ms) java.lang.NullPointerException at org.jgroups.protocols.UNICAST2.triggerXmit(UNICAST2.java:1326) at org.jgroups.protocols.UNICAST2$RetransmitTask.run(UNICAST2.java:1294) at org.jgroups.util.TimeScheduler2$RecurringTask.run(TimeScheduler2.java:591) at org.jgroups.util.TimeScheduler2$MyTask.run(TimeScheduler2.java:523) at org.jgroups.util.TimeScheduler2$Entry.execute(TimeScheduler2.java:428) at org.jgroups.util.TimeScheduler2$1.run(TimeScheduler2.java:286) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:662) {code} Theoretically there is another race condition in the {{SenderEntry.getFirstMessage()}} itself - the low value may change between the {{getLow}} and {{get}} calls, but I am not sure when this may happen.