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From "Jeff Trawick" <>
Subject Re: debug apache
Date Mon, 19 Jun 2006 11:07:00 GMT
On 6/18/06, Ruediger Pluem <> wrote:
> On 06/18/2006 04:03 PM, Jeff Trawick wrote:
> >> > On 06/17/2006 08:57 AM, Alexander Lazic wrote:
> >> > > On Sam 17.06.2006 00:54, Ruediger Pluem wrote:
> >> > >> From my current point of view the answer is: No, this is not
> >> possible
> >> > >> out of the box.
> >> > >> It may be possible if you modify the hook macros.
> >
> >
> > yep
> >
> > Getting inside these macros is what enables diagnostic features such as
> >
> > a) mod_status display of where a request is being held up
> But this feature is not in our codebase, right? Is it a patch to the macros
> + an additional module that hooks itself into the status_hook? Just curious.

not in our code base

what I do is replace stuff like

  ap_run_handler (a macro)


  foo_run_handler (a function)

which will check ap_extended_status; if off, it will just "return
otherwise, it essentially has the macro expansion, but it has the
following logic around the module call:

  worker_score->module_index = handler_modindexes[n];
  rv = pHook[n].dummy(r);
  if (rv != DECLINED) {
    worker_score->module_index = 0;
    return rv;

If we reach the end without a module handling it:
  worker_score->module_index = 0;
  return DECLINED;

At initialization, the handler_modindexes function is built to
correspond to the hook_array.

Meanwhile, mod_status and a few other diagnostic modules know how to
turn a module index into a module name.

I put this problem determination aid in four hook calls which have
proven interesting w.r.t. third-party modules: handler, access
checker, check user id, log transaction.  I didn't care about any
performance difference between a hook macro in mainline vs. call to a
function which checks ap_extended_status and then invokes the macro.
I did check the CPU usage difference between ExtendedStatus on and
ExtendedStatus off after adding this logic.  It is still in the
neighborhood of a 1-2% increase, which is well worth it.


dev@httpd or dev@apr?

Implementation wise, what we are using is not a simple function call
or two which could be cleanly inserted into the apr-util hook macro
expansion.  The problem determination aid is dependent on

* the data structures behind the hook macros
* the Apache module index, which needs to be stored in those data
structures or in a parallel data structure so that it can be accessed
efficiently while walking through the hook array
* the worker_score

If httpd *developers* are interested, we should decide what type of
processing is acceptable/required first and worry about whether it can
be fitted into apr second.  As I recall from the last discussion of
this perhaps 15 months ago, most all of the interest was from web
admin lurkers, and there was insufficient developer interest anyway.

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