[jira] [Comment Edited] (THRIFT-3932) C++ ThreadManager has a rare termination race

["Buğra Gedik (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/THRIFT-3932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15538134#comment-15538134 ] 

Buğra Gedik edited comment on THRIFT-3932 at 10/1/16 8:02 AM:
--------------------------------------------------------------

Looks good to me. Great work!


was (Author: bgedik):
Looks good to me.

> C++ ThreadManager has a rare termination race
> ---------------------------------------------
>
>                 Key: THRIFT-3932
>                 URL: https://issues.apache.org/jira/browse/THRIFT-3932
>             Project: Thrift
>          Issue Type: Bug
>          Components: C++ - Library
>            Reporter: Buğra Gedik
>            Assignee: James E. King, III
>         Attachments: thrift-patch
>
>          Time Spent: 8h
>  Remaining Estimate: 0h
>
> {{ThreadManger::join}} calls {{stopImpl(true)}}, which in turn calls {{removeWorker(workerCount_);}}. The latter waits until {{while (workerCount_ != workerMaxCount_)}}. Within the {{run}} method of the workers, the last thread that detects {{workerCount_ == workerMaxCount_}} notifies {{removeWorker}}. The {{run}} method has the following additional code that is executed at the very end:
> {code}
>     {
>       Synchronized s(manager_->workerMonitor_);
>       manager_->deadWorkers_.insert(this->thread());
>       if (notifyManager) {
>         manager_->workerMonitor_.notify();
>       }
>     }
> {code}
> This is an independent synchronized block. Now assume 2 threads. One of them has {{notifyManager=true}} as it detected the {{workerCount_ == workerMaxCount_}} condition earlier. It is possible that this thread gets to execute  the above code block first, {{ThreadManager}}'s {{removeWorker}} method unblocks, and eventually {{ThreadManager}}'s {{join}} returns and the object is destructed. When the other thread reaches the synchronized block above, it will crash, as the manager is not around anymore.
> Besides, {{ThreadManager}} never joins its threads.
> Attached is a patch.



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