Re: [ANN] - curl-loader virtual scripting in SVN

[Michael M. <mos...@gm...>]

Hi,

I have looked into LUA, now lets try to reconstruct the reasoning (any
corrections/suggestions are welcome).

Our problem here is that we need several thousand simulated clients in one
process;

This poses the following question
1) do we have one virtual machine for each simulated  client, i.e. a
scripting language thread per client.
2) doe we have one virtual machine for all simulated clients.

We will come back to that question later.

Now lets look at the basic problem that we are facing with integrating any
language environment with server that is processing requests asynchronously
- xmethod calls (ie. calls to external methods written in C) usually these
calls are blocking.

[ the script would need at least one xmethod call that would perform the
next http request that would 1) initiate the http request, 2) suspend
execution of the vm for the current thread 3) be able to resume current
thread when needed]

now this problem can be solved by longjumps (or any other coprocedure
mechanism) at the expense of  some memory to hold the current stack when we
suspend current xmethod. Now

basically this kills the option  of using one vm for all simulated clients.

Ok, lets assume we are using longjump, this rules our sharing one vm for all
simulated clients,
How? lua is singlethreaded and with longjump we just suspended the current
thread that is running the vm, [also any pending lock will block the whole
VM if we branch out of it.]

Ok, now we have one VM per simulated client. Great, with LUA they have a
garbage collected heap, and holding such a heap per each simulated client is
a very large overhead.
(even if we could share one vm for all simulated clients then this garbage
collection schema is a real killer for predictable and reasonable
performance)


Our requirements is therefore
- vm supports xmethod calls that are truly asynchronous,  without  need for
longjumps.
- VM with very low footprint
- memory management for objects created by the script that is reference
counted;
- also when a VM exits it has to take its memory with it.


2008/4/30 Aleksandar Lazic <al-...@no...>:

> Hi,
>
> On Fre 30.11.2007 10:41, Robert Iakobashvili wrote:
>
> > Gentlemen,
> >
> > Michael Moser has checked-in a new system for HTTP/FTP response body
> > analyses, which have WebLoad and JMeter tools.
> >
> > Normally, body analyses in testing tools is done using JavaScript or
> > any other script, which occupies a total thread, is blocking and is bad
> > for performance.
> >
> > Since curl-loader is about performance (written in C, using C-written
> > stacks of libcurl and openssl) Michael is developing a new scripting
> > language, where the script will be:
> >
>
> yust for my curiosity, have you looked into neko, lua or some other
> 'smalll and embadabble' language and found some nogos?!
>
> Cheers
>
> Aleks
>