On Wed, Jul 22, 2009 at 11:12 AM, ghtdak<gl...@tarbox.org> wrote:
>
>
>
> On Jul 21, 6:40 pm, "Dr. David Kirkby" <david.kir...@onetel.net>
> wrote:
>> ghtdak wrote:
>>
>> > This thread has gotten long and there are many subjects embedded
>> > within.
>>
>> > One of the problems I've had with the notebook implementation is that
>> > the sage process supporting the notebook computation blocks on the
>> > pipe between itself and the twistd server which spawns it. This means
>> > that one can't build an asynchronous event handler without using
>> > threads.
>>
>> > More conventional web server architectures use a callback style for
>> > invocation making it much easier to splice in other events for
>> > handling by the main thread (this is the general asynchronous
>> > programming model and the heart of how Twisted works)
>>
>> > Perhaps it is a foregone conclusion that this approach will be taken
>> > in the rewrite. if not, I'd like to suggest that it is an important
>> > consideration.
>>
>> > -glenn
>>
>> I don't know about how the web server is implemented. I know it did not
>> work on my Solaris box, but that is another matter.
>>
>> But actually including Apache might be a sensible choice. A lot of
>> people know how to administer Apache. It offers a lot of flexibility.
>> You can for example only serve pages to particular IP addresses.
>>
>> Worth a thought anyway.
>
> I came across this post from the Twisted folks. It looks like they do
> WSGI and run Django quite well...
>
> http://blog.dreid.org/2009/03/twisted-django-it-wont-burn-down-your.html
>
> At least there are alternatives to apache which might be simpler.
>
> The core question remains: While the presentation layer support is
> defined by django, pyjamas etc, the integration with the underlying
> sage process process is the issue, not the web presentation.
>
> In the current architecture, a twistd daemon spawns a notebook server
> which is responsible for doing "sage" stuff. twistd is fully
> asynchronous, but the notebook process itself is a pexpect based
> blocking process connected with pipes to twistd. As such, the block
> on read by pexpect precludes the sage process servicing asynchronous
> events.
Here's the relevant code that you're talking about (starting at line
3007 of worksheet.py):
try:
done, out, new = S._so_far(wait=wait,
alternate_prompt=SAGE_END+str(self.synchro()))
except RuntimeError, msg:
verbose("Computation was interrupted or failed.
Restarting.\n%s"%msg)
self.__comp_is_running = False
self.start_next_comp()
return 'w', C
The Sage notebook server does a blocking read from the
pexpect-controlled subprocess for "wait" seconds. The default value
of wait is 0.2 seconds. So indeed there is a block, but it is never
for more than 0.2 seconds. During that time other asynchronous
events can't be dealt with.
> IMHO, this architecture is incorrect and limited... Perhaps this is
> part of what is being rethought... if not, I believe it should be.
>
> A preferable architecture is an event loop which dispatches requests
> within the sage process. Since Sage is written in python, I would
> suggest Twisted for this but there might be better alternatives (I'd
> be surprised, but its possible)
>
> Using this approach, one could easily add other elements to the core
> event loop to support asynchronous processing (timers, communication,
> etc) without threads which are, in this case, unnecessary. Threads
> when necessary are bad enough, when they're introduced because of
> unnecessary blocking, one gets all the threading nightmare without any
> benefit. (reminds me of health care reform)
>
> Another benefit is that since asynchronous event processing is the
> widely accepted approach to this type of problem, there are lots of
> libraries / packages to "make it so".
>
> -glenn
>
>>
>> dave
> >
>
--
William Stein
Associate Professor of Mathematics
University of Washington
http://wstein.org
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