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From "Roland Weber (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HTTPCLIENT-633) MultiThreadedHttpConnectionManager does not properly respond to thread interrupts
Date Fri, 16 Feb 2007 16:13:05 GMT

    [ https://issues.apache.org/jira/browse/HTTPCLIENT-633?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473740

Roland Weber commented on HTTPCLIENT-633:

Hi all,

one more alternative, which Mike already mentioned on the dev list:
(3) Re-throw InterruptedException as a RuntimeException, for example IllegalThreadStateException

I'm also for re-throwing, and a RuntimeException would make sure that this doesn't trigger
application code explicitly handling the ConnectionManagerTimeoutException exception. Yes
it's an API change, but one that only affects the application in situations where MTHCM would
be screwing up. Applications that work correctly now will work correctly despite the change,
and applications that fail because of the RuntimeException will be better off than before,
where they would fail in some unpredictable way because of the corrupted state in MTHCM.

That we can't reliably tell whether there is an external InterruptedException or not can't
be helped. If the thread was interrupted just after getting the connection, it would simply
return with the connection and have it's interrupted flag set. I don't see a problem with
keeping this behavior if two interruptions occur in quick succession.


> MultiThreadedHttpConnectionManager does not properly respond to thread interrupts
> ---------------------------------------------------------------------------------
>                 Key: HTTPCLIENT-633
>                 URL: https://issues.apache.org/jira/browse/HTTPCLIENT-633
>             Project: HttpComponents HttpClient
>          Issue Type: Bug
>          Components: HttpConn
>    Affects Versions: 3.1 Beta 1
>            Reporter: John Goodwin
>         Attachments: mthcm-interruption.patch
> MultiThreadedHttpConnectionManager uses interrupts to notify waiting threads when a connection
is ready for them. Issues arise if the threads are interrupted by someone else while they
are still waiting on a thread, because doGetConnection does not remove the threads from the
queue of waiting threads when they are interrupted:
>                         connectionPool.wait(timeToWait);
>                         // we have not been interrupted so we need to remove ourselves
from the 
>                         // wait queue
>                         hostPool.waitingThreads.remove(waitingThread);              
>                     } catch (InterruptedException e) {
>                         // do nothing                    } finally {
>                         if (useTimeout) {
>                             endWait = System.currentTimeMillis();
>                             timeToWait -= (endWait - startWait);                    
   }                    }
> Under ordinary circumstances, the queue maintenance is done by the notifyWaitingThread
method. However, if the thread is interrupted by any other part of the system, it will (1)
not actually be released, since the loop in doGetConnection will force it back to the wait,
and (2) will be added the waiting thread to the queue repeatedly, which basically means that
the thread will eventually receive the interrupt from notifyWaitingThread at some later point,
when it is no longer actually waiting for a connection.
> This code could probably be re-architected to make it less error-prone, but the fundamental
issue seems to be the use of interrupts to signal waiting threads, as opposed to something
like a notify. 

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