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From "Chuan Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9916) Race condition in ipc.Client causes TestIPC timeout
Date Mon, 02 Sep 2013 23:22:51 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9916?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13756263#comment-13756263

Chuan Liu commented on HADOOP-9916:

This is a very good analysis of the race condition.
I can verify that the patch also fixes the problem in HADOOP-9896.
> Race condition in ipc.Client causes TestIPC timeout
> ---------------------------------------------------
>                 Key: HADOOP-9916
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9916
>             Project: Hadoop Common
>          Issue Type: Bug
>            Reporter: Binglin Chang
>            Assignee: Binglin Chang
>            Priority: Minor
>         Attachments: HADOOP-9916.v1.patch
> TestIPC timeouts occasionally, for example: 
> [https://issues.apache.org/jira/browse/HDFS-5130?focusedCommentId=13749870&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13749870]
> [https://issues.apache.org/jira/browse/HADOOP-9915?focusedCommentId=13753302&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13753302]
> Look into the code, there is race condition in oah.ipc.Client, the race condition happen
between RPC call thread and connection read response thread:
> {code}
>         if (status == RpcStatusProto.SUCCESS) {
>           Writable value = ReflectionUtils.newInstance(valueClass, conf);
>           value.readFields(in);                 // read value
>           call.setRpcResponse(value);
>           calls.remove(callId);
> {code}
> Read Thread: 
> Connection.receiveRpcResponse-> call.setRpcResponse(value) -> notify Call Thread
> Call Thread:
> Client.call -> Connection.addCall(retry with the same callId) -> notify read thread
> Read Thread:
> calls.remove(callId) # intend to remove old call, but removes newly added call...
> Connection.waitForWork end up wait maxIdleTime and close the connection. The call never
get response and dead.
> The problem doesn't show because previously callId is unique, we never accidentally remove
newly added calls, but when retry added this race condition became possible.
> To solve this, we can simply change order, remove the call first, then notify call thread.
> Note there are many places need this order change(normal case, error case, cleanup case)
> And there are some minor issues in TestIPC:
> 1. there are two method with same name:
>    void testSerial()
>    void testSerial(int handlerCount, boolean handlerSleep, ...)
>    the second is not a test case(so should not use testXXX prefix), but somehow it causes
testSerial(first one) run two times, see test report:
> {code}
>   <testcase time="26.896" classname="org.apache.hadoop.ipc.TestIPC" name="testSerial"/>
>   <testcase time="25.426" classname="org.apache.hadoop.ipc.TestIPC" name="testSerial"/>
> {code}
> 2. timeout annotation should be added, so next time related log is available.

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