Re[2]: multi-threaded Emacs

Re[2]: multi-threaded Emacs

[ak70]

Hi, guys. I have a generic user-level thread library on Linux. Maybe it can help.
The thread system is called SMASH developed by Kurt Debattista in 2001 as his master study in University of Malta. 
It uses the two level scheduling model, i.e. we have m user level threads running on top of n kernel threads. If you guys are interested,
I can send you the thesis about it( it is a pdf file of size 1Mb). 
A few month ago, I obtained the permission from Kurt to release it under GPL. I did some work on it too for my undergraduate study.
The problems:
1. It is platform dependent. Kurt and I used some x86 assembly language to implement spin locks and lock-free algorithms.
2. It lacks some common features that you would expect in a thread library. For example it has no thread id and when a user-level terminates,
the thread structure will not be destroyed. This is however done on purpose, because our  supervisor argued that SMASH should be at the lowest
level so that any fancy(or not so fancy) features should be implemented by other libraries built on top of it.
3. Since it is developed as a academic project, a lot of decisions were made in favor of our study, not production use.

I think it is a good starting point, but it is not for immediate use. So what you guys think? Are you interested?
> -----Original Message-----
> From: Giuseppe Scrivano <gscrivano@gnu.org>
> To: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: rms@gnu.org, emacs-devel@gnu.org
> Date: 12/02/08 23:41
> Subject: Re: multi-threaded Emacs
> 
> Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
> 
> > I rarely use multiple terminals, and when I use them, the current
> > restrictions are mostly bearable.  OTOH I very often would like to keep
> > using my Emacs while it's byte-compiling some files, or while Gnus is
> > fetching some newsgroup.
> 
> This is exactly the problem I had when I first thought of threads.
> 
> Do you think we can solve it (at least partially) using a concurrent
> model?
> 
> Thanks,
> Giuseppe

Re: multi-threaded Emacs

[Richard M Stallman]

It could be a useful package to develop further, for general purposes.
I cannot tell whether it might be useful in Emacs because your message
does not address the crucial questions.

    It uses the two level scheduling model, i.e. we have m user level
    threads running on top of n kernel threads.

Is the distinction between user-level threads and kernel threads
a matter of optimization, or is it a user-level feature?

Under what circumstances does it switch threads?

For the user, how does this differ from pthreads?

Re: multi-threaded Emacs

[Li Lin]

First, all context switches between user-level threads have to be done
manually, i.e. if you need a switch, you have to call
cthread_yield(). However, on SMP systems, since we have more than one
kernel threads, user-level threads may be interrupted randmonly, but
still no user-level context switch will happen unless you yield the CPU explicitly.

Re: multi-threaded Emacs

[Giuseppe Scrivano]

Personally I don't think there is need to use a library that at the
moment is usable only on an architecture, it will be a serious
portability problem for Emacs (that probably after "Hello World" is the
most portable program out there).
All we need for a multi-threaded Emacs can be done quite easily with
pthreads.

Giuseppe

Li Lin <ak70@vanilla.net.mt> writes:

> SMASH has many different implementations. Basically, we create one
> kernel thread for each CPU(or core) in which a user-level thread
> scheduler runs, and the thread is bounded to the corresponding CPU. The
> context switches among user-level threads are done though a explicit
> call to the function cthread_yield(). However, it is the native
> scheduler that manages the kernel threads. 
> So on uniprocessor machines, it is purely cooperative, on multi-CPU(or
> -core) machines it is a mixture of cooperative and preemptive
> threads. However, it is not difficult to modify it so that on
> uniprocessor machine we still have more than one kernel threads.
> I attached Kurt's thesis about SMASH. Although a lot of implementation
> details has changed, his orginal thesis is still a good reference.
> The attachment is a DVI file. If you can read it, then I can send you
> the latex source of it, but you have to compile it by yourself.

Re: multi-threaded Emacs

[Magnus Henoch]

Giuseppe Scrivano <gscrivano@gnu.org> writes:

> Personally I don't think there is need to use a library that at the
> moment is usable only on an architecture, it will be a serious
> portability problem for Emacs (that probably after "Hello World" is the
> most portable program out there).
> All we need for a multi-threaded Emacs can be done quite easily with
> pthreads.

Or GNU pth, which I'm surprised that noone has mentioned.  It does
cooperative threading with a pthread-like interface, yielding at I/O
operations and some other syscalls.

http://www.gnu.org/software/pth/

Of course, whoever writes the code gets to choose the library.  Good
luck with your endeavour!  I look forward to the results.

Magnus

Re: multi-threaded Emacs

[Stefan Monnier]

> Hi, guys.  I have a generic user-level thread library on Linux.
> Maybe it can help.

Thanks.  But note that the problem with Emacs and cuncurrency doesn't
have much to do with the presence or absence of threads libraries.
There are already plenty of libraries implementing threads.  The problem
to change Emacs's Lisp and C code so as to be able to take advantage
of them.


        Stefan