[Caml-list] Pre-emptive multitasking

[Caml-list] Pre-emptive multitasking

[Jonathan Roewen]

Hi,

Does the OCaml runtime support true pre-emptive multitasking with the
systhreads module? Am curious how this works with the GC without
breaking anything.

Jonathan

Re: [Caml-list] Pre-emptive multitasking

[Richard Jones]

On Sun, Jun 12, 2005 at 08:51:44AM +1200, Jonathan Roewen wrote:
> Does the OCaml runtime support true pre-emptive multitasking with the
> systhreads module? Am curious how this works with the GC without
> breaking anything.

The GC isn't thread-safe.  This means that when OCaml code runs, it
must be protected by a global mutex.  If you have two threads running
OCaml code, they will contend for this mutex, and run (around) 50% of
the time each.  If you have two CPUs you won't gain any benefit.  The
standard solution would be to run one OCaml thread and lots of C
threads, or else use fork(2) to create one separate process for each
processor and use shared memory, sockets, pipes, etc. for
communication.

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
Team Notepad - intranets and extranets for business - http://team-notepad.com

Re: [Caml-list] Pre-emptive multitasking

[Jonathan Roewen]

> The GC isn't thread-safe. 

What would it take to make it thread-safe? I plan to make a custom
native code runtime anyway, so could try working on that problem
too...

> This means that when OCaml code runs, it
> must be protected by a global mutex.  If you have two threads running
> OCaml code, they will contend for this mutex, and run (around) 50% of
> the time each.  If you have two CPUs you won't gain any benefit. 

We plan on running separate runtimes for multi-processor systems.

> The standard solution would be to run one OCaml thread and lots of C
> threads

This is not a solution: we're going for an almost pure OCaml operating
system (need asm, etc). I'm more interested in the ins and outs of the
scheduler for pure OCaml threading. Such as, is it pre-emptive or
co-operative? What kind of runtime guarantees can it provide for near
realtime applications, etc.

Jonathan

Re: [Caml-list] Pre-emptive multitasking

[Benjamin Geer]

On 12/06/05, Jonathan Roewen <jonathan.roewen@gmail.com> wrote:
> > The GC isn't thread-safe.
> 
> What would it take to make it thread-safe?

This has come up before on this list; see these posts by Xavier Leroy:

http://groups-beta.google.com/group/fa.caml/msg/acd4b247c3fcb1cd
http://groups-beta.google.com/group/fa.caml/msg/ca7279b03517cbc4

Ben

Re: [Caml-list] Pre-emptive multitasking

[Jonathan Roewen]

> This has come up before on this list; see these posts by Xavier Leroy:

Yes, but the difference this time is that OCaml -is- the operating system =)

> http://groups-beta.google.com/group/fa.caml/msg/acd4b247c3fcb1cd
> http://groups-beta.google.com/group/fa.caml/msg/ca7279b03517cbc4

Thanks for those links :-) An interesting read.

And where could I find this concurrent caml light implementation?
Seems like it could well do as a starting point for a new OCaml GC for
our project.

Jonathan