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From "Chuck Williams (JIRA)" <j...@apache.org>
Subject [jira] Updated: (AXIS2-4800) Http connection listener terminates when request executor full
Date Wed, 18 Aug 2010 05:27:16 GMT

     [ https://issues.apache.org/jira/browse/AXIS2-4800?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Chuck Williams updated AXIS2-4800:
----------------------------------

    Attachment: DefaultConnectionListener.patch

Patch to org.apache.axis2.transport.http.server.DefaultConnectionListener so that if an http
request cannot be processed due to RejectedExecutionException the service returns http 503
Service Unavailable instead of shutting down the connection listener.


> Http connection listener terminates when request executor full
> --------------------------------------------------------------
>
>                 Key: AXIS2-4800
>                 URL: https://issues.apache.org/jira/browse/AXIS2-4800
>             Project: Axis2
>          Issue Type: Bug
>          Components: transports
>    Affects Versions: 1.6, 1.5.2, 1.5.1, 1.5, nightly
>         Environment: Any
>            Reporter: Chuck Williams
>         Attachments: DefaultConnectionListener.patch
>
>   Original Estimate: 0.5h
>  Remaining Estimate: 0.5h
>
> The DefaultConnectionListener of the built-in http server invokes the failure apparatus
in the configured ConnectionListenerFailureHandler when exceptions arise handing off a new
request connection to an HttpServiceProcessor.  The built-in failure apparatus in DefaultConnectionListenerFailureHandler
retries (default 10 times) and then gives up, after which the DefaultConnectionListener shuts
down.  This permanently closes the port, rendering the web service unreachable.  One can replace
the DefaultConnectionListenerFailureHandler easily by overriding HttpFactory.newRequestConnectionListener(),
however the failure processing methods do not have access to the request connection and thus
cannot take any action that requires sending a response back to the client.
> A particularly important case arises when the http request executor's thread pool and
backing queue are both full.  In this case the attempt to launch a thread to process the new
http request gets RejectedExecutionException.  The server should return an http 503 Service
Unavailable, since it has already accessed the new connection and so cannot refuse it.  This
is impossible to achieve with the existing failure apparatus because it can't send a response.
 The result is that the when the web service becomes overloaded the connection listener permanently
shuts down!
> The failure apparatus is actually a patch of mine from a few years ago.  At the time
any failure would immediately shut down the connection listener and I added some simple processing
for the case of an intermittent issue.  The new case of RejectedExecutionException is clearly
an important one and I've prepared a new patch (to be attached next) that fixes this by sending
503 Service Unavailable whenever the request executor cannot accept a new request after the
connection listener has already accepted the request connection.
> I would have committed this, but since I've been inactive in axis2 development for some
time that seemed unwise.  An active developer should probably first weigh in.  I have tested
the patch successfully in an application that requires it.
> More should be done here.  Failure cases in the connection listener are important as
the consequences of improper handling are dire, leaving your web service unreachable.  Probably
there are additional cases that should be built in, and the extensible failure apparatus should
be generalized so that it can send responses whenever a request has already been accepted
but the normal processing fails back to the listener.

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