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From "hector rovira (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HTTPCLIENT-814) MultiThreadedHttpConnectionManager deadlocks when reusing socket connections
Date Wed, 09 Sep 2009 23:27:57 GMT

    [ https://issues.apache.org/jira/browse/HTTPCLIENT-814?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12753325#action_12753325
] 

hector rovira commented on HTTPCLIENT-814:
------------------------------------------

I have been able to reproduce this bug.  This is also an issue for me.  Timeouts don't seem
to be having an effect.  I would upgrade to 4.0, but can't right now.  

Here's the snippet of code where I'm accessing the HttpClient (v.3.1).  (Pls ignore ResponseCallback
and my custom exceptions).  It blocks on the httpClient.executeMethod.  Setting log4j.xml
to debug showed that the org.apache.commons.httpclient.MultiThreadedHttpConnectionManager
"Unable to get a connection, waiting..."

    public Object executeMethod(HttpMethod method, ResponseCallback responseCallback) throws
HttpClientException, HttpClientResponseException {
            try {
                int statusCode = httpClient.executeMethod(method);
                log.info("executeMethod(" + method.getPath() + "):" + statusCode);
                return responseCallback.onResponse(statusCode, method);
            } catch (IOException e) {
                throw new HttpClientException(method, e);
            } finally {
                method.releaseConnection();
            }
    }

My workaround is to use the org.apache.commons.httpclient.SimpleHttpConnectionManager instead,
and add a synchronization block to avoid multiple threads using the httpclient at the same
time.

> MultiThreadedHttpConnectionManager deadlocks when reusing socket connections
> ----------------------------------------------------------------------------
>
>                 Key: HTTPCLIENT-814
>                 URL: https://issues.apache.org/jira/browse/HTTPCLIENT-814
>             Project: HttpComponents HttpClient
>          Issue Type: Bug
>          Components: HttpClient
>    Affects Versions: 3.1 Final
>         Environment: Tomcat 6.18 running on a Windows 2003 server
>            Reporter: Will Franco
>             Fix For: Future
>
>
> During our Load Testing we encountered that the MultiThreadedHttpConnectionManager deadlocks
when reusing socket connections.   These socket connections remain in the pool in a CLOSE_WAIT
state, and the pool is unable to reuse them or create new ones because the maximum number
of connection has already been reached, thus deadlocking.
> Let me explain briefly how this library is being used and the temporary work around that
we are using.  However, the correct solution would be to use the connection pool.
> Usage:
> 1) The HttPClient is being used to handle connections to another server from our Web
Application.  So far, for every request our Web App processes we have to make at least one
request to another server using the HttpClient.
> 2) Our load tester, loads our web app with thousands of requests within the first 30
seconds, and maintains such high volume of requests for at least 24 hours
> Work Around:
> The current work around we implemented is to have different HttpClient instances per
request, and we shutdown the Connection Manager once we complete the transaction with the
other server.
> The next work around we will be trying is to call the closeIdleConnections, this solution
will remove the connections that can potentially deadlock the connection manager allowing
it to allocate new ones.
> Please email me to willfranco@gmail.com if you need any further information regarding
this issue.

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