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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (THRIFT-3891) TNonblockingServer configured with more than one IO threads does not always return from serve() upon stop()
Date Wed, 25 Jan 2017 04:46:26 GMT

    [ https://issues.apache.org/jira/browse/THRIFT-3891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15837187#comment-15837187
] 

ASF GitHub Bot commented on THRIFT-3891:
----------------------------------------

Github user jeking3 commented on a diff in the pull request:

    https://github.com/apache/thrift/pull/1080#discussion_r97708735
  
    --- Diff: lib/cpp/src/thrift/server/TNonblockingServer.cpp ---
    @@ -1524,7 +1532,7 @@ void TNonblockingIOThread::breakLoop(bool error) {
       }
     
       // sets a flag so that the loop exits on the next event
    -  event_base_loopbreak(eventBase_);
    +  event_base_loopexit(eventBase_, 0);
    --- End diff --
    
    I am curious to understand why this was changed.  event_base_loopexit will cause the lop
to continue processing until drained.  This function is called breakLoop and I assume that
means stop as soon as possible, which is what it was doing.


> TNonblockingServer configured with more than one IO threads does not always return from
serve() upon stop()
> -----------------------------------------------------------------------------------------------------------
>
>                 Key: THRIFT-3891
>                 URL: https://issues.apache.org/jira/browse/THRIFT-3891
>             Project: Thrift
>          Issue Type: Bug
>          Components: C++ - Library
>    Affects Versions: 0.9.3
>            Reporter: Buğra Gedik
>            Priority: Minor
>         Attachments: patch.diff
>
>
> Using {{TNonblockingServer}}, when the number of IO threads is > 1, there is race
condition in which {{stop()}} does not properly unblock {{serve()}}. 
> The problem manifests itself when {{stop()}} is called (obviously from a different thread)
soon after {{serve()}}. 
> The core issue is that, {{event_base_loopbreak()}} is called within the {{stop()}} sequence
without checking whether the IO thread has actually entered its event loop. The documentation
of {{event_base_loopbreak()}} says (http://www.wangafu.net/~nickm/libevent-book/Ref3_eventloop.html)
> {quote}
> Note also that event_base_loopexit(base,NULL) and event_base_loopbreak(base) act differently
when no event loop is running: loopexit schedules the next instance of the event loop to stop
right after the next round of callbacks are run (as if it had been invoked with EVLOOP_ONCE)
whereas loopbreak only stops a currently running loop, and has no effect if the event loop
isn’t running.
> {quote}
> Attached is a patch (against the released 0.9.3 version of the codebase).



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