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From Justin Erenkrantz <jus...@erenkrantz.com>
Subject Re: Event MPM
Date Tue, 26 Oct 2004 18:29:14 GMT
--On Tuesday, October 26, 2004 1:53 PM -0400 Greg Ames 
<gregames@remulak.net> wrote:

> right, I understand.  check_pipeline_flush already tests whether the
> input filters hold any data if I'm not mistaken.

It doesn't quite work like that.  check_pipeline_flush (via the EATCRLF 
get_brigade call) only does anything if there are stray CRLFs after a 
request - it doesn't return any knowledge if there is a request pending. 
(In fact, EATCRLF will actually read the data from the socket into 
core_input_filter's buffer - so it'll directly cause the poll() to not work 
correctly.)  For example, when mod_ssl is active, an EATCRLF call always 
returns ENOTIMPL.  So, the check_pipeline_flush doesn't always work as 
expected and the EATCRLF check isn't enough to determine if there is any 
'held' data.

> not if we modify it so that the worker thread doesn't give up the
> connection to the event thread when there is more data in the input
> filters.  That's what I meant by "react appropriately".  Sorry if I
> wasn't clear.

The problem is that there is no reliable way to determine if there is more 
data in the input filters without actually invoking a read. 
Connection-level filters like mod_ssl would have to be rewritten to be 
async.  SPECULATIVE with APR_NONBLOCK_READ will come the closest to 
achieving the goal though.  However, I expect mod_ssl isn't going to work 
quite right with non-blocking reads.

Trying to support both 'slow' *and* 'fast' connections I think will require 
changes outside of the scope of the MPM.  This is why I'd prefer branching 
2.3 and work on it in there: these changes are likely to snowball.  Plus, 
this effort dovetails with trying to rethink how filters work.  -- justin

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