[jboss-jira] [JBoss JIRA] Commented: (JGRP-812) NakReceiverWindow: possible race condition

NakReceiverWindow: possible race condition ------------------------------------------ Key: JGRP-812 URL: https://jira.jboss.org/jira/browse/JGRP-812 Project: JGroups Issue Type: Bug Reporter: Bela Ban Assignee: Bela Ban Fix For: 2.7 [Randy Watler] I just ran into a really rare race condition that appears to be in NakReceiverWindow that occurred on a cluster member when another member was shutdown. I believe what happened here was the NakReceiverWindow for the node that left was reset, but then a late message was received from that node with an old sequence number that was greater than 200000000. The window then attempted to create that many NULL_MSG entries in the xmit_table and blew out the heap. Here is my somewhat circumstantial evidence for this claim. I managed to catch a thread adding a NULL_MSG to the xmit_table when the cluster should have been generally quiescent: "Incoming,cache,10.129.1.202:9931" prio=10 tid=0x000000005dac5800 nid=0x790d runnable [0x00000000412e5000..0x00000000412e5a80] java.lang.Thread.State: RUNNABLE at java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:883) at org.jgroups.stack.NakReceiverWindow.add(NakReceiverWindow.java:294) at org.jgroups.protocols.pbcast.NAKACK.handleMessage(NAKACK.java:802) at org.jgroups.protocols.pbcast.NAKACK.up(NAKACK.java:672) at org.jgroups.protocols.BARRIER.up(BARRIER.java:122) at org.jgroups.protocols.VERIFY_SUSPECT.up(VERIFY_SUSPECT.java:167) at org.jgroups.protocols.FD.up(FD.java:322) at org.jgroups.protocols.FD_SOCK.up(FD_SOCK.java:300) at org.jgroups.protocols.MERGE2.up(MERGE2.java:145) at org.jgroups.protocols.Discovery.up(Discovery.java:246) at org.jgroups.protocols.TP$IncomingPacket.handleMyMessage(TP.java:1535) at org.jgroups.protocols.TP$IncomingPacket.run(TP.java:1479) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907) at java.lang.Thread.run(Thread.java:619) Here is the related NakReceiverWindow code: 287 // Case #4: we received a seqno higher than expected: add NULL_MSG values for missing messages, add to Retransmitter 288 if(seqno > next_to_add) { 289 if(listener != null) { 290 try {listener.messageGapDetected(next_to_add, seqno, msg.getSrc());} catch(Throwable t) {} 291 } 292 293 for(long i=next_to_add; i < seqno; i++) { // add all msgs (missing or not) into table 294 xmit_table.put(i, NULL_MSG); 295 } 296 xmit_table.put(seqno, msg); 297 retransmitter.add(old_next, seqno -1); // BUT: add only null messages to xmitter 298 return true; 299 } By itself this certainly could be circumstantial, but this thread was captured while the JVM heap was being actively consumed and GC was taking over the machine resources. The following heap profile was captured along with the thread above: num #instances #bytes class name ---------------------------------------------- 1: 57613383 2765442384 java.util.concurrent.ConcurrentHashMap$HashEntry 2: 57578762 1381890288 java.lang.Long 3: 1824 1117553680 [Ljava.util.concurrent.ConcurrentHashMap$HashEntry; 4: 104423 11514120 [C Obviously, that is a big and growing ConcurrentHashMap keyed by Long... seems like it could be the xmit_table above. We have logging on for jgroups protocols. Here is the NAKACK messages log line BEFORE the heap started to be consumed: cache NAKACK msgs: 10.129.1.241:9931: [214528761 : 214531351 (214531351)]; 10.129.1.131:9931: [487104 : 487111 (487111)]; 10.129.1.203: 9931: [130428 : 130429 (130429)]; 10.129.1.202:9931: [123991 : 123994 (123994) (size=3, missing=0, highest stability=123991)]; 10.129.1.132: 9931: [487597 : 487601 (487601)]; 10.129.1.201:9931: [147919 : 147923 (147923)]; 10.129.1.133:9931: [487203 : 487209 (487209)]; 10.129.1.134 :9931: [487666 : 487668 (487668)] and after: cache NAKACK msgs: 10.129.1.131:9931: [487126 : 487138 (487138)]; 10.129.1.203:9931: [130433 : 130434 (130434)]; 10.129.1.202:9931: [12 3997 : 123998 (123998) (size=1, missing=0, highest stability=123997)]; 10.129.1.132:9931: [487619 : 487636 (487636)]; 10.129.1.201:9931: [14 7936 : 147940 (147940)]; 10.129.1.133:9931: [487222 : 487244 (487244)]; 10.129.1.134:9931: [487678 : 487696 (487696)] So, its pretty clear that the 10.129.1.241 node left the view and its last sequence number was approximately 214531351. That number is sufficiently large to explain the fact I was able to catch this behavior, the fact that it was consuming the heap, and apparently had already added 57M entries to some ConcurrentHashMap. Logging in GMS and NAKACK also verified the view change: 2008-08-12 03:52:51,088 DEBUG [FD_SOCK pinger,cache,10.129.1.202:9931]: org.jgroups.protocols.FD_SOCK - peer closed socket normally 2008-08-12 03:52:51,184 DEBUG [FD_SOCK pinger,cache,10.129.1.202:9931]: org.jgroups.protocols.FD_SOCK - pinger thread terminated 2008-08-12 03:52:51,189 DEBUG [Incoming,cache,10.129.1.202:9931]: org.jgroups.protocols.pbcast.GMS - view=[10.129.1.131:9931|8] [10.129.1.1 31:9931, 10.129.1.132:9931, 10.129.1.133:9931, 10.129.1.134:9931, 10.129.1.203:9931, 10.129.1.201:9931, 10.129.1.202:9931] 2008-08-12 03:52:51,193 DEBUG [Incoming,cache,10.129.1.202:9931]: org.jgroups.protocols.pbcast.GMS - [local_addr=10.129.1.202:9931] view is [10.129.1.131:9931|8] [10.129.1.131:9931, 10.129.1.132:9931, 10.129.1.133:9931, 10.129.1.134:9931, 10.129.1.203:9931, 10.129.1.201:9931, 10 .129.1.202:9931] 2008-08-12 03:52:51,194 WARN [Incoming,cache,10.129.1.202:9931]: org.jgroups.protocols.pbcast.NAKACK - 10.129.1.202:9931] discarded message from non-member 10.129.1.241:9931, my view is [10.129.1.131:9931|7] [10.129.1.131:9931, 10.129.1.132:9931, 10.129.1.133:9931, 10.129.1.134: 9931, 10.129.1.203:9931, 10.129.1.201:9931, 10.129.1.202:9931, 10.129.1.241:9931] 2008-08-12 03:52:51,195 INFO [Incoming,cache,10.129.1.202:9931]: com.getmedium.medium.cache.lateral.endpoint.LateralCacheEndpoint - Current membership for cache group: [10.129.1.131:9931, 10.129.1.132:9931, 10.129.1.133:9931, 10.129.1.134:9931, 10.129.1.203:9931, 10.129.1.201:99 31, 10.129.1.202:9931] 2008-08-12 03:52:51,201 DEBUG [Incoming,cache,10.129.1.202:9931]: org.jgroups.protocols.pbcast.GMS - sending VIEW_ACK to 10.129.1.131:9931 2008-08-12 03:52:51,201 DEBUG [Timer,null,null]: org.jgroups.protocols.FD_SOCK - VIEW_CHANGE received: [10.129.1.131:9931, 10.129.1.132:993 1, 10.129.1.133:9931, 10.129.1.134:9931, 10.129.1.203:9931, 10.129.1.201:9931, 10.129.1.202:9931] 2008-08-12 03:52:51,201 WARN [Incoming,cache,10.129.1.202:9931]: org.jgroups.protocols.pbcast.NAKACK - 10.129.1.202:9931] discarded message from non-member 10.129.1.241:9931, my view is [10.129.1.131:9931|8] [10.129.1.131:9931, 10.129.1.132:9931, 10.129.1.133:9931, 10.129.1.134: 9931, 10.129.1.203:9931, 10.129.1.201:9931, 10.129.1.202:9931] 2008-08-12 03:52:51,201 WARN [Incoming,cache,10.129.1.202:9931]: org.jgroups.protocols.pbcast.NAKACK - 10.129.1.202:9931] discarded message from non-member 10.129.1.241:9931, my view is [10.129.1.131:9931|8] [10.129.1.131:9931, 10.129.1.132:9931, 10.129.1.133:9931, 10.129.1.134: 9931, 10.129.1.203:9931, 10.129.1.201:9931, 10.129.1.202:9931] 2008-08-12 03:52:51,201 DEBUG [FD_SOCK pinger,cache,10.129.1.202:9931]: org.jgroups.protocols.FD_SOCK - pinger_thread started Upon inspecting the code in NakReceiverWindow, it seems plausible to me that a message arrived in add() just after the view was adjusted and reset() was called. Given that the sequence numbers are fairly high in this case, its easy to see why that tight loop in add() might attempt what is trying to do here. Does this scenario seem possible as I present it? If so, is there a way to bound "case#4" and/or shutdown the add() after a reset? Unfortunately, this is the ONLY time I have seen this behavior in over 2 years of working with JGroups, so I do not expect to be able to reproduce it again for another year. I just happened to catch it this time around in a state where I was able to diagnose it to some degree before the JVM went dark. Please let me know if I can help diagnose this further. Randy Watler