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From "Uwe Schindler (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3803) Using a searcher with an executor service does not work from within a Callable called by that same executor service
Date Mon, 20 Feb 2012 01:00:56 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13211622#comment-13211622
] 

Uwe Schindler commented on LUCENE-3803:
---------------------------------------

The problem is that you are using the same fixed thread pool for everything. If you only have
1 or 2 threads in the pool (as noted in your mail) and one of those threads calls searcher.search()
from within its own callable, searcher.search will try to execute the sub-searches in its
own callables. If the thread pool does not have enough free threads, it will wait for a thread
to get available (because another callable finishes). The callable that called searcher.search
will of course not finish as it waits for itsself to finish -> deadlock.

The bad idea with thread pools that leads to your problem is: Don't start Callables from within
another Callable in the same thread pool. This almost always leads to deadlocks.
                
> Using a searcher with an executor service does not work from within a Callable called
by that same executor service
> -------------------------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-3803
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3803
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: core/search
>    Affects Versions: 3.5
>            Reporter: Benson Margulies
>         Attachments: lucene-tc.tgz
>
>
> The test case I'm about to attach creates an executor service uses invokeAll to run things
from it. The 'things' (Callable) that it runs in turn run Lucene searchers using a searcher
that has the very same executor service. This turns out to hit some sort of deadlock related
to the executor service queue. 
> I won't be terribly surprised if this is really a matter of a fundamental limitation
of the executor service, but if nothing else this JIRA might provoke a warning in the javadoc.
Or, what do I know, maybe there's a way Lucene could interact with the executor service that
gets along with this?

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