[ZOOKEEPER-4673] Deadlock in zookeeper client. - ASF JIRA

Details

Type: Bug
Status: Open
Priority: Major
Resolution: Unresolved
Affects Version/s: 3.4.13
Fix Version/s: None
Component/s: java client
Labels:
None

Description

We use apache curator 2.10.0 version
We use zookeeper some version of 3.4.13 (I know its very old. ) We also have cherry-picked ~~ZOOKEEPER-2251~~ in our branch.

Threads in deadlock.

Found one Java-level deadlock:
=============================
"Curator-Framework-0":
  waiting to lock monitor 0x00007f34f2163a00 (object 0x00007f344228db00, a java.util.LinkedList),
  which is held by "Curator-Framework-0-SendThread(<zk server>:2181)"
"Curator-Framework-0-SendThread(<zk server>:2181)":
  waiting to lock monitor 0x00007f2109731980 (object 0x00007f2270fd02a8, a org.apache.curator.ConnectionState),
  which is held by "Curator-Framework-0"



"Curator-Framework-0" #1493 daemon prio=5 os_prio=0 cpu=98.73ms elapsed=50812.45s tid=0x00007f2128da5de0 nid=0x2889 waiting for monitor entry  [0x00007f2053436000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at org.apache.zookeeper.ClientCnxn$SendThread.cleanup(ClientCnxn.java:1245)
        - waiting to lock <0x00007f344228db00> (a java.util.LinkedList)
        at org.apache.zookeeper.ClientCnxn$SendThread.cleanAndNotifyState(ClientCnxn.java:1174)
        at org.apache.zookeeper.ClientCnxn$SendThread.access$2300(ClientCnxn.java:700)
        at org.apache.zookeeper.ClientCnxn.submitRequest(ClientCnxn.java:1420)
        at org.apache.zookeeper.ClientCnxn.close(ClientCnxn.java:1373)
        at org.apache.zookeeper.ZooKeeper.close(ZooKeeper.java:788)
        - locked <0x00007f344228cd78> (a org.apache.zookeeper.ZooKeeper)
        at org.apache.curator.HandleHolder.internalClose(HandleHolder.java:139)
        at org.apache.curator.HandleHolder.closeAndReset(HandleHolder.java:77)
        at org.apache.curator.ConnectionState.reset(ConnectionState.java:217)
        - locked <0x00007f2270fd02a8> (a org.apache.curator.ConnectionState)
        at org.apache.curator.ConnectionState.checkTimeouts(ConnectionState.java:193)
        - locked <0x00007f2270fd02a8> (a org.apache.curator.ConnectionState)
        at org.apache.curator.ConnectionState.getZooKeeper(ConnectionState.java:88)
        at org.apache.curator.CuratorZookeeperClient.getZooKeeper(CuratorZookeeperClient.java:116)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.performBackgroundOperation(CuratorFrameworkImpl.java:835)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.backgroundOperationsLoop(CuratorFrameworkImpl.java:809)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.access$300(CuratorFrameworkImpl.java:64)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl$4.call(CuratorFrameworkImpl.java:267)
        at java.util.concurrent.FutureTask.run(java.base@11.0.16.1.1/FutureTask.java:264)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(java.base@11.0.16.1.1/ScheduledThreadPoolExecutor.java:304)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base@11.0.16.1.1/ThreadPoolExecutor.java:1128)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base@11.0.16.1.1/ThreadPoolExecutor.java:628)
        at java.lang.Thread.run(java.base@11.0.16.1.1/Thread.java:829)


"Curator-Framework-0-SendThread(<zkserver>:2181)" #1524807 daemon prio=5 os_prio=0 cpu=25.58ms elapsed=101.61s tid=0x00007f1f3836d0c0 nid=0x113ad waiting for monitor entry  [0x00007f212767b000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at org.apache.curator.ConnectionState.checkTimeouts(ConnectionState.java:176)
        - waiting to lock <0x00007f2270fd02a8> (a org.apache.curator.ConnectionState)
        at org.apache.curator.ConnectionState.getZooKeeper(ConnectionState.java:88)
        at org.apache.curator.CuratorZookeeperClient.getZooKeeper(CuratorZookeeperClient.java:116)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.performBackgroundOperation(CuratorFrameworkImpl.java:835)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.doSyncForSuspendedConnection(CuratorFrameworkImpl.java:701)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.access$700(CuratorFrameworkImpl.java:64)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl$7.retriesExhausted(CuratorFrameworkImpl.java:697)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.checkBackgroundRetry(CuratorFrameworkImpl.java:716)
        at org.apache.curator.framework.imps.CuratorFrameworkImpl.processBackgroundOperation(CuratorFrameworkImpl.java:516)
        at org.apache.curator.framework.imps.BackgroundSyncImpl$1.processResult(BackgroundSyncImpl.java:50)
        at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:611)
        at org.apache.zookeeper.ClientCnxn$EventThread.queuePacket(ClientCnxn.java:462)
        - locked <0x00007f344228e0c0> (a java.util.concurrent.LinkedBlockingQueue)
        at org.apache.zookeeper.ClientCnxn.finishPacket(ClientCnxn.java:632)
        at org.apache.zookeeper.ClientCnxn.conLossPacket(ClientCnxn.java:650)
        at org.apache.zookeeper.ClientCnxn.access$2100(ClientCnxn.java:94)
        at org.apache.zookeeper.ClientCnxn$SendThread.cleanup(ClientCnxn.java:1246)
        - locked <0x00007f344228db00> (a java.util.LinkedList)
        at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1159)

In 3.4.13 version, ClientCnxn#outgoingQueue type is LinkedList NOT LinkedBlockingDeque and we have many places where we synchronize on outgoingQueue.

The client application was spending lot of time in garbage collection and the request to server were timing out.
Logline from CuratorFramework-0 thread before the jstack

 2023-02-03 08:29:41:973 #1493 Timeout error occurred for the packet clientPath:null serverPath:null finished:false header:: 0,-11  replyHeader:: 0,0,0  request:: null response:: null

Logline from CuratorFramework-0-SendThread thread before the jstack.

2023-02-03 08:29:26:371 #1524807 Opening socket connection to server <zk server>:2181. Will attempt to SASL-authenticate using Login Context section 'Client'
2023-02-03 08:29:26.371 #1524807 Socket connection established to <zk server>:2181, initiating session
2023-02-03 08:29:26.388 #1524807 Unable to reconnect to ZooKeeper service, session 0x1002232ea037548 has expired

Curator-Framework-0 thread acquired org.apache.curator.ConnectionState lock and waiting for ClientCnxn#outgoingQueue lock
Curator-Framework-0-SendThread acquired ClientCnxn#outgoingQueue lock and waiting for org.apache.curator.ConnectionState lock.

From the above thread dump, Curator-Framework-0 is trying to call SendThread#cleanAndNotifyState which is NOT correct. In my opinion it should just interrupt the sendThread and let SendThread cleanup its state.
Here is the relevant code link

        if (r.getErr() == Code.REQUESTTIMEOUT.intValue()) {
            sendThread.cleanAndNotifyState(); ---> We should NOT call this directly instead call sendThread.interrupt and let it clean its state.
        }

Deadlock in zookeeper client.

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