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From shinrich <>
Subject [GitHub] trafficserver pull request #787: TS-4507: Fix SSN and TXN hook ordering.
Date Sat, 02 Jul 2016 13:29:16 GMT
GitHub user shinrich opened a pull request:

    TS-4507: Fix SSN and TXN hook ordering.

    This change was motivated by dealing with ordering problems between SSN_CLOSE and TXN_CLOSE
causing problems (crashes).  This we addressed as follows
      * The TXN_CLOSE is kicked off in the State Machine kill_this.  This is the point were
we know that the TXN really is going away.  This is unchanged.  What this patch adds is a
call to transaction_done to let the ClientTransaction know that TXN_CLOSE has completed so
the calculation about whether is it time to execute SSN_CLOSE or not.  As such we cannot null
out ua_session early.
    * To support SSN_CLOSE accurately, we split the destroy logic into two parts: destroy
and free.  Destroy commits to deleting the session and it kicks off the SSN_CLOSE plugin.
free performs the final resource reclamation of the session object.
    In addition this PR includes the following fixes.
        In ProxyClientSession::state_api_callout we schedule_in 10ms in the future if the
plugin lock is not acquired. Saw ASAN use-after-free crashes when the Http2ClientSession is
deleted but the schedule event remains and is triggered. Added a schedule_event member to
track this case and cancel any outstanding schedule events on free.
        Cleaned up handling regular events at the same time as plugin events. The original
code relied on the subclasses overriding handle_api_event to handle the regular events, but
the handler only handled the TIMEOUT event. Changed that to augment the subclasses' main event
handler to call out to state_api_callout in the event of the plugin events.

You can merge this pull request into a Git repository by running:

    $ git pull ts-4507-2

Alternatively you can review and apply these changes as the patch at:

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #787
commit ce7f22609b169b48e4883375ec42e78996827614
Author: Susan Hinrichs <>
Date:   2016-07-02T13:10:11Z

    TS-4507: Fix SSN and TXN hook ordering.


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