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From "Chen Liang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14519) Client$Connection#waitForWork may suffer spurious wakeup
Date Mon, 12 Jun 2017 20:45:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16047047#comment-16047047
] 

Chen Liang commented on HADOOP-14519:
-------------------------------------

Thanks [~jzhuge] for the catch! The patch LGTM. One minor thing though, I think the patch
slightly changed the syntax of this function. (Please correct me if I'm wrong though).

Let's denote condition {{calls.isEmpty() && !shouldCloseConnection.get() &&
running.get()}} as condition A. The original logic works that, it only checks A before calling
wait, meaning when it gets notified, it returns from wait and just proceed, potentially possible
that A is still true at this point. While the patch changes it that, even when it gets notified,
as long as A is true, it will keep looping. Could you please verify that this change to the
syntax is correct? I'm inclined to believe it is all good based the fact of no test failures.


> Client$Connection#waitForWork may suffer spurious wakeup
> --------------------------------------------------------
>
>                 Key: HADOOP-14519
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14519
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: ipc
>    Affects Versions: 2.8.0
>            Reporter: John Zhuge
>            Assignee: John Zhuge
>            Priority: Critical
>         Attachments: HADOOP-14519.001.patch
>
>
> {{Client$Connection#waitForWork}} may suffer spurious wakeup because the {{wait}} is
not surrounded by a loop. See [https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait()].
> {code:title=Client$Connection#waitForWork}
>       if (calls.isEmpty() && !shouldCloseConnection.get() && running.get())
 {
>         long timeout = maxIdleTime-
>               (Time.now()-lastActivity.get());
>         if (timeout>0) {
>           try {
>             wait(timeout);                          <<<<<<==== spurious
wakeup
>           } catch (InterruptedException e) {}
>         }
>       }
> {code}



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