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From "Chuck Williams (JIRA)" <j...@apache.org>
Subject [jira] Created: (AXIS2-4800) Http connection listener terminates when request executor full
Date Wed, 18 Aug 2010 05:23:16 GMT
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: 1.5, 1.5.1, 1.6, 1.5.2, nightly
         Environment: Any
            Reporter: Chuck Williams


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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