Faking concurrency using Unix forks and pipes

Faking concurrency using Unix forks and pipes

[Jon Harrop]

Has anyone implemented a parallel map function in OCaml using Unix forks, 
pipes and maybe marshalling?

This seems like an easy way to get concurrency in OCaml...

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Erik de Castro Lopo]

Jon Harrop wrote:

> 
> Has anyone implemented a parallel map function in OCaml using Unix forks, 
> pipes and maybe marshalling?

I've been thinking of something like that, but with sockets 
replacing pipes so its possible to do distributed as well as
parallel programming. I was actually going to do C at the
lowest level (for generality more than anything else) and put 
an Ocaml wrapper around it.

Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"Perl as a language has less a design than a thousand special
features flying in close formation."
-- From the c2 wiki

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jonathan Bryant]

On May 29, 2007, at 11:42 PM, Jon Harrop wrote:

>
> Has anyone implemented a parallel map function in OCaml using Unix  
> forks,
> pipes and maybe marshalling?

I've implemented a toy version of this, so I can say it does work and  
is not too hard, although I don't still have the code.  My OSP  
project is a concurrency library that would make implementing this  
pretty trivial though: it extends the Event module to work over UNIX  
& TCP sockets and to have a common interface for thread creation /  
forking / remote process creation.

>
> This seems like an easy way to get concurrency in OCaml...

It would also be nice to have a Apply in Parallel / Parallel List  
Comprehension syntax for it a la NESL (http://www.cs.cmu.edu/~scandal/ 
nesl.html).

>
> -- 
> Dr Jon D Harrop, Flying Frog Consultancy Ltd.
> OCaml for Scientists
> http://www.ffconsultancy.com/products/ocaml_for_scientists/?e
>
> _______________________________________________
> Caml-list mailing list. Subscription management:
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Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Benedikt Grundmann]

Hello,

I'm also doing an OSP project on concurrency.  In my case there will
actually be a new api which will offer erlang style concurrency (e.g.
asynchroneous messages).  (Also implemented using UNIX & TCP sockets).

Cheers,

Bene

PS: I already have some code that does the local message passing, but
it is all in a flux and I consider that a prototype, so hold your
breath until August.


2007/5/30, Jonathan Bryant <jtbryant@valdosta.edu>:
>
> On May 29, 2007, at 11:42 PM, Jon Harrop wrote:
>
> >
> > Has anyone implemented a parallel map function in OCaml using Unix
> > forks,
> > pipes and maybe marshalling?
>
> I've implemented a toy version of this, so I can say it does work and
> is not too hard, although I don't still have the code.  My OSP
> project is a concurrency library that would make implementing this
> pretty trivial though: it extends the Event module to work over UNIX
> & TCP sockets and to have a common interface for thread creation /
> forking / remote process creation.
>
> >
> > This seems like an easy way to get concurrency in OCaml...
>
> It would also be nice to have a Apply in Parallel / Parallel List
> Comprehension syntax for it a la NESL (http://www.cs.cmu.edu/~scandal/
> nesl.html).
>
> >
> > --
> > Dr Jon D Harrop, Flying Frog Consultancy Ltd.
> > OCaml for Scientists
> > http://www.ffconsultancy.com/products/ocaml_for_scientists/?e
> >
> > _______________________________________________
> > Caml-list mailing list. Subscription management:
> > http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
> > Archives: http://caml.inria.fr
> > Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> > Bug reports: http://caml.inria.fr/bin/caml-bugs
>
> _______________________________________________
> Caml-list mailing list. Subscription management:
> http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
> Archives: http://caml.inria.fr
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>


-- 
Calvin: I try to make everyone's day a little more
surreal.

(From Calvin & Hobbes)

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Oliver Bandel]

Hi,

On Wed, May 30, 2007 at 04:42:59AM +0100, Jon Harrop wrote:
> 
> Has anyone implemented a parallel map function in OCaml using Unix forks, 
> pipes and maybe marshalling?

I have thought about such stuff, but ot implemented
(because there was no real need for it).

Since I found OCamlP3l, I'm not shure if implementing
such stuff would make sense, because using OCamlP3l
might be the right way.

  OCamlP3l: http://camlp3l.inria.fr/eng.htm

I didn't tried it so far.

If people already have done (or will do now),
I would be interested in feedback.

Ciao,
   Oliver

P.S.: Why did you  write "Faking concurrency"?
      If the processes are running on a multi-core/multi-processor
      machine, using processes can achieve paralellism.

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jon Harrop]

On Wednesday 30 May 2007 08:02:30 Oliver Bandel wrote:
> I have thought about such stuff, but ot implemented
> (because there was no real need for it).

I feel dirty when one of my cores is idling.

> Since I found OCamlP3l, I'm not shure if implementing
> such stuff would make sense, because using OCamlP3l
> might be the right way.
>
>   OCamlP3l: http://camlp3l.inria.fr/eng.htm

May I just ask Xavier et al. what the ETA is on ocamlp3l? Its just, I really 
want to take over the world and this is holding us up. ;-)

> P.S.: Why did you  write "Faking concurrency"?
>       If the processes are running on a multi-core/multi-processor
>       machine, using processes can achieve paralellism.

Well, yes, I mean it is the ugly sister of concurrent GC. Better than nothing 
though.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[David Teller]

Great, another one of my splendid ideas of concurrency, being already
done by someone smarter than me. Gosh.

Well, I'll just return to work on my static analyser...

Cheers,
 David

On Wed, 2007-05-30 at 08:31 +0100, Jon Harrop wrote:
> > Since I found OCamlP3l, I'm not shure if implementing
> > such stuff would make sense, because using OCamlP3l
> > might be the right way.
> >
> >   OCamlP3l: http://camlp3l.inria.fr/eng.htm
> 
> May I just ask Xavier et al. what the ETA is on ocamlp3l? Its just, I really 
> want to take over the world and this is holding us up. ;-)

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Loup Vaillant]

2007/5/30, Oliver Bandel <oliver@first.in-berlin.de>:
> Hi,
>
> On Wed, May 30, 2007 at 04:42:59AM +0100, Jon Harrop wrote:
> >
> > Has anyone implemented a parallel map function in OCaml using Unix forks,
> > pipes and maybe marshalling?
>
> [...]
> Since I found OCamlP3l, I'm not shure if implementing
> such stuff would make sense, because using OCamlP3l
> might be the right way.
> [...]

I've just read some of the user manual, and can notice a small
syntactic burden, as well as the unavoidable fact that one must learn
it to use it. (This is not a complaint. Any library is like that.)

Jon, were you talking about reimplementing List.map and the like, so
users have concurrency for free? A simple solution would be to use a
third party tool, like OcamlP3l.

Cheers,
Loup Vaillant

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jon Harrop]

On Wednesday 30 May 2007 08:34:48 Loup Vaillant wrote:
> Jon, were you talking about reimplementing List.map and the like, so
> users have concurrency for free?

Exactly, yes. Just having a concurrent Array.map would help enormously.

> A simple solution would be to use a third party tool, like OcamlP3l.

I'm having a look at it now. I had thought that it was an experimental version 
of OCaml that with a concurrent GC but that seems to be completely wrong.

Will OCaml have a concurrent GC in the future?

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Erik de Castro Lopo]

Jon Harrop wrote:

> I'm having a look at it now. I had thought that it was an experimental version 
> of OCaml that with a concurrent GC but that seems to be completely wrong.
> 
> Will OCaml have a concurrent GC in the future?

How much does a concurrent GC actually buy in comparison to 
multiple processes each with their own GC and a robust way
of passing data between processes?

Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"The day Microsoft makes something that doesn't suck is probably the
day they start making vacuum cleaners." -- Ernst Jan Plugge

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Loup Vaillant]

2007/5/30, Erik de Castro Lopo <mle+ocaml@mega-nerd.com>:
> Jon Harrop wrote:
>
> > I'm having a look at it now. I had thought that it was an experimental version
> > of OCaml that with a concurrent GC but that seems to be completely wrong.
> >
> > Will OCaml have a concurrent GC in the future?
>
> How much does a concurrent GC actually buy in comparison to
> multiple processes each with their own GC and a robust way
> of passing data between processes?
>

As far as I know, the developement team had made it quite clear that
there will be no concurent GC (not in the near future, at least).


> Erik
> --
> -----------------------------------------------------------------
> Erik de Castro Lopo
> -----------------------------------------------------------------
> "The day Microsoft makes something that doesn't suck is probably the
> day they start making vacuum cleaners." -- Ernst Jan Plugge
>
> _______________________________________________
> Caml-list mailing list. Subscription management:
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> Bug reports: http://caml.inria.fr/bin/caml-bugs
>

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Loup Vaillant]

2007/5/30, Erik de Castro Lopo <mle+ocaml@mega-nerd.com>:
> Jon Harrop wrote:
>
> > I'm having a look at it now. I had thought that it was an experimental version
> > of OCaml that with a concurrent GC but that seems to be completely wrong.
> >
> > Will OCaml have a concurrent GC in the future?
>
> How much does a concurrent GC actually buy in comparison to
> multiple processes each with their own GC and a robust way
> of passing data between processes?
>

As far as I know, the developement team had made it quite clear that
there will be no concurent GC (not in the near future, at least). The
main reason is performance loss.

(Sorry for the double post)

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jon Harrop]

On Wednesday 30 May 2007 09:32:48 Loup Vaillant wrote:
> As far as I know, the developement team had made it quite clear that
> there will be no concurent GC (not in the near future, at least). The
> main reason is performance loss.

Might be interesting to compare the performance of some languages using my ray 
tracer:

C++: 3.67s
OCaml: 3.97s
F#: 5.26s
Lisp: 6.04s
Scheme: 6.29s
Java: 6.53s

F# is ~30% slower than OCaml but can be made almost twice as fast on my dual 
core machine by tracing concurrently. However, Java is also a concurrent 
static language and it is much slower. Maybe this reflects more effort having 
gone into the .NET GC.

I should also note that the F# and Scheme are both 32-bit. I wonder how well 
F# would do if it were 64-bit... :-)

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Richard Jones]

On Wed, May 30, 2007 at 09:50:35AM +0100, Jon Harrop wrote:
> F# is ~30% slower than OCaml but can be made almost twice as fast on my dual 
> core machine by tracing concurrently. However, Java is also a concurrent 
> static language and it is much slower. Maybe this reflects more effort having 
> gone into the .NET GC.

Jon,

We've had this discussion before.  Summary: yes, SMP is suddenly
popular.  If we keep doubling the number of cores available every 18
months though, then soon we'll have dozens-hundreds of cores, and
there's no chance at all that these will have uniform memory access.
Once you have NUMA, threads and concurrent GC don't help.

Intel 80 core processor:
http://www.reghardware.co.uk/2006/09/26/intel_teraflop_processor/ ,
and it's very very NUMA - each core has 20 MB of RAM strapped to it.
>From the article: "[The chip] also features a network processing unit
on each core to control core-to-core communication. [...] Once Intel
boffins have worked out the best way to interconnect cores, memory [...]"

Rich.


-- 
Richard Jones
Red Hat

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jon Harrop]

On Wednesday 30 May 2007 09:13:00 Erik de Castro Lopo wrote:
> How much does a concurrent GC actually buy in comparison to
> multiple processes each with their own GC and a robust way
> of passing data between processes?

1. Shared memory and locks should be much faster for synchronization than 
marshalling between processes.

2. Forking results in multiple GCs redundantly traversing the same heap and, 
worst case, it may end up copying the entire heap in the child process in 
order to deallocate it.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Mattias Engdegård]

>> How much does a concurrent GC actually buy in comparison to
>> multiple processes each with their own GC and a robust way
>> of passing data between processes?
>
>1. Shared memory and locks should be much faster for synchronization than 
>marshalling between processes.
>
>2. Forking results in multiple GCs redundantly traversing the same heap and, 
>worst case, it may end up copying the entire heap in the child process in 
>order to deallocate it.

3. Cores on the same chip often share at least one cache level,
   and the same is trivially true for threads in the same core.
   In software-speak, this means that processes should share the read-only
   part of their working set as much as possible.

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Richard Jones]

On Wed, May 30, 2007 at 09:54:32AM +0100, Jon Harrop wrote:
> On Wednesday 30 May 2007 09:13:00 Erik de Castro Lopo wrote:
> > How much does a concurrent GC actually buy in comparison to
> > multiple processes each with their own GC and a robust way
> > of passing data between processes?
> 
> 1. Shared memory and locks should be much faster for synchronization than 
> marshalling between processes.
> 
> 2. Forking results in multiple GCs redundantly traversing the same heap and, 
> worst case, it may end up copying the entire heap in the child process in 
> order to deallocate it.

Fixed: http://merjis.com/developers/ancient

Rich.

-- 
Richard Jones
Red Hat

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Pablo Polvorin]

> 1. Shared memory and locks should be  much faster
> for synchronization than  marshalling between processes.

as long as i don't have to use ugly locks in my code, that will be ok.
But I think that the Erlang approach is simpler and more elegant than
the use of locks - critical regions. Also, as already mentioned, it
offers an easy transition from multicore to distributed computing,
where shared memory isn't available.


2007/5/30, Jon Harrop <jon@ffconsultancy.com>:
> On Wednesday 30 May 2007 09:13:00 Erik de Castro Lopo wrote:
> > How much does a concurrent GC actually buy in comparison to
> > multiple processes each with their own GC and a robust way
> > of passing data between processes?
>

>
> 2. Forking results in multiple GCs redundantly traversing the same heap and,
> worst case, it may end up copying the entire heap in the child process in
> order to deallocate it.
>
> --
> Dr Jon D Harrop, Flying Frog Consultancy Ltd.
> OCaml for Scientists
> http://www.ffconsultancy.com/products/ocaml_for_scientists/?e
>
> _______________________________________________
> Caml-list mailing list. Subscription management:
> http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
> Archives: http://caml.inria.fr
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>


-- 
Pablo Polvorin

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Erik de Castro Lopo]

Jon Harrop wrote:

> 1. Shared memory and locks should be much faster for synchronization than 
> marshalling between processes.

Shared memory and locking becomes completely intractable beyond about 
10 cores and Intel is already talking about 80 cores.
 
> 2. Forking results in multiple GCs redundantly traversing the same heap and, 
> worst case, it may end up copying the entire heap in the child process in 
> order to deallocate it.

To exploit multi-process message-passing style concurrency you need to 
fork early before much has been allocated.

Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"... a discussion of C++'s strengths and flaws always sounds
like an argument about whether one should face north or east
when one is sacrificing one's goat to the rain god."
-- Thant Tessman

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Florian Hars]

Jon Harrop schrieb:
> Has anyone implemented a parallel map function in OCaml using Unix forks, 
> pipes and maybe marshalling?

I've been toying with something like

module type MR =
  functor (D1: DICT_TYPE) ->
    functor (D2: DICT_TYPE) ->
sig
  val mapreduce :
    (D1.key -> D1.value -> (D2.key * 'a) list) ->
    ( D2.key -> 'a list -> D2.value option) ->
    D1.t ->
    D2.t
end

and have one implementation that forks a set of worker processes
and then marshalls data of types
type 'a command = Quit | Execute of 'a
type ('a, 'b) response = Result of 'a | Error of 'b
through a pipe.

Not very robust right now, but it seems to work if none of the
workers dies prematurely...

Yours Florian.

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Gerd Stolpmann]

Am Mittwoch, den 30.05.2007, 09:13 +0200 schrieb Florian Hars:
> Jon Harrop schrieb:
> > Has anyone implemented a parallel map function in OCaml using Unix forks, 
> > pipes and maybe marshalling?
> 
> I've been toying with something like
> 
> module type MR =
>   functor (D1: DICT_TYPE) ->
>     functor (D2: DICT_TYPE) ->
> sig
>   val mapreduce :
>     (D1.key -> D1.value -> (D2.key * 'a) list) ->
>     ( D2.key -> 'a list -> D2.value option) ->
>     D1.t ->
>     D2.t
> end

Interesting example... We are going to implement a distributed mapreduce
on a cluster using ocamlnet (and its components rpc and netplex).

Netplex is a framework to listen to a number of sockets and to
start/manage processes dealing with the TCP connections (using a
generalized pre-fork model). We are already using it for our distributed
web crawler.

Gerd

> and have one implementation that forks a set of worker processes
> and then marshalls data of types
> type 'a command = Quit | Execute of 'a
> type ('a, 'b) response = Result of 'a | Error of 'b
> through a pipe.
> 
> Not very robust right now, but it seems to work if none of the
> workers dies prematurely...
> 
> Yours Florian.
> 
> _______________________________________________
> Caml-list mailing list. Subscription management:
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> Bug reports: http://caml.inria.fr/bin/caml-bugs
> 
-- 
------------------------------------------------------------
Gerd Stolpmann * Viktoriastr. 45 * 64293 Darmstadt * Germany 
gerd@gerd-stolpmann.de          http://www.gerd-stolpmann.de
Phone: +49-6151-153855                  Fax: +49-6151-997714
------------------------------------------------------------

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Luc Maranget]

> 
> Has anyone implemented a parallel map function in OCaml using Unix forks, 
> pipes and maybe marshalling?
> 
> This seems like an easy way to get concurrency in OCaml...
> 
> -- 
> Dr Jon D Harrop, Flying Frog Consultancy Ltd.
> OCaml for Scientists
> http://www.ffconsultancy.com/products/ocaml_for_scientists/?e


This is what we did for a a few examples of using JoCaml,
the soon-to-be-released extension of OCaml for concurrent programming.

Fork/Exec is an easy way to get simultaneous execution.

JoCaml is not released yet, (I am writting the doc
and web site at the moment).

The much incomplete web site is at
<http://jocaml.inria.fr>

One example of fork under jocaml control
<http://jocaml.inria.fr/manual/concurrent.html#htoc25>

The example may not meet all your concerns (speed I guess),
but you can replace the shell in the example by somme
C or Ocaml program that computes something and refine the control
to collect results.


Hope it helps.

-- 
Luc Maranget

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Erik de Castro Lopo]

Luc Maranget wrote:

> This is what we did for a a few examples of using JoCaml,
> the soon-to-be-released extension of OCaml for concurrent programming.
> 
> Fork/Exec is an easy way to get simultaneous execution.
> 
> JoCaml is not released yet, (I am writting the doc
> and web site at the moment).
> 
> The much incomplete web site is at
> <http://jocaml.inria.fr>

Now that *really* *does* look interesting!

Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"It has been discovered that C++ provides a remarkable facility
for concealing the trival details of a program -- such as where
its bugs are." -- David Keppel

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Erik de Castro Lopo]

Erik de Castro Lopo wrote:

> > The much incomplete web site is at
> > <http://jocaml.inria.fr>
> 
> Now that *really* *does* look interesting!

I tried to grab the source tarball, but got a 404 not found :-(.

Patience Erik, patience!

Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
Diana West for President of the United States
http://www.washtimes.com/op-ed/20060817-091447-7758r.htm
http://www.washtimes.com/op-ed/20060824-084015-5082r.htm

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jon Harrop]

On Wednesday 30 May 2007 10:25:08 Erik de Castro Lopo wrote:
> Erik de Castro Lopo wrote:
> > > The much incomplete web site is at
> > > <http://jocaml.inria.fr>
> >
> > Now that *really* *does* look interesting!
>
> I tried to grab the source tarball, but got a 404 not found :-(.
>
> Patience Erik, patience!

This is outrageous. We could have had JoCaml by now if Luc hadn't been posting 
on mailing lists. I'm shocked and appalled...

By the way, apologies to the ten people who downloaded my original bytecode 
tarball of Smoke that had dependencies on other code that wasn't there. It 
should all be fixed now. Why does nobody ever tell me whether or not my demos 
work?! :-)

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Joel Reymont]

On May 30, 2007, at 10:25 AM, Jon Harrop wrote:

> Why does nobody ever tell me whether or not my demos work?! :-)

This off-topic but it must be basic human psychology or something.

The same thing happens with my translator.

	Joel

--
http://topdog.cc      - EasyLanguage to C# translator
http://wagerlabs.com  - Blog

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[David Teller]

Because we assumed we were just too stupid to get them to work. Or at
least I did.

Cheers,
 David

On Wed, 2007-05-30 at 10:25 +0100, Jon Harrop wrote:
> On Wednesday 30 May 2007 10:25:08 Erik de Castro Lopo wrote:
> > Erik de Castro Lopo wrote:
> > > > The much incomplete web site is at
> > > > <http://jocaml.inria.fr>
> > >
> > > Now that *really* *does* look interesting!
> >
> > I tried to grab the source tarball, but got a 404 not found :-(.
> >
> > Patience Erik, patience!
> 
> This is outrageous. We could have had JoCaml by now if Luc hadn't been posting 
> on mailing lists. I'm shocked and appalled...
> 
> By the way, apologies to the ten people who downloaded my original bytecode 
> tarball of Smoke that had dependencies on other code that wasn't there. It 
> should all be fixed now. Why does nobody ever tell me whether or not my demos 
> work?! :-)
> 

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Joel Reymont]

On May 30, 2007, at 9:40 AM, Luc Maranget wrote:

> This is what we did for a a few examples of using JoCaml,
> the soon-to-be-released extension of OCaml for concurrent programming.

Tell me, please tell me, it does not require me to install another  
OCaml compiler source tree!

I'm yearning for a concurrent OCaml extension that uses Camlp4 and  
generates plain OCaml code. Is there such a thing?

	Thanks, Joel

--
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Re: [Caml-list] Faking concurrency using Unix forks and pipes

[David Teller]

JoCaml has (nearly) returned !
Yeah !
Happiness and tears of joy !

David,
 who will now stop spamming people with Erlang and return to advocating
JoCaml.

On Wed, 2007-05-30 at 10:40 +0200, Luc Maranget wrote:
> JoCaml is not released yet, (I am writting the doc
> and web site at the moment).
> 
> The much incomplete web site is at
> <http://jocaml.inria.fr>
> 
> One example of fork under jocaml control
> <http://jocaml.inria.fr/manual/concurrent.html#htoc25>
> 
> The example may not meet all your concerns (speed I guess),
> but you can replace the shell in the example by somme
> C or Ocaml program that computes something and refine the control
> to collect results.
> 
> 
> Hope it helps.
> 

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Thomas Fischbacher]

Jon Harrop wrote:

> Has anyone implemented a parallel map function in OCaml using Unix forks, 
> pipes and maybe marshalling?
> 
> This seems like an easy way to get concurrency in OCaml...

That is indeed an exercise I like to pose to my PhD students.
(Of course, the question whether this really makes that much
sense is a different issue...)


Here is my own suggestion how to do it:


let compute_uniform_workload_forked
     ?(bailout=
	(fun str ->
	   let () = Printf.fprintf stderr "AIEE! %s\n%!" str in
	     exit 1))
     ~fun_combine
     v_work =
   let bailout s dummy = let _ = bailout s in dummy in
     (* Note that we use the "bailout" function in two different places 
where it expects
        different return types. Hence, we have to bend over backwards to 
get the type
        system to accept what we actually want to do...
     *)
   let nr_processes = Array.length v_work in
   let rec setup_childs nr_process child_info =
     if nr_process = nr_processes
     then List.rev child_info (* This ensures we get the data in proper 
order. *)
     else
       let (fd_read,fd_write) = Unix.socketpair Unix.PF_UNIX 
Unix.SOCK_STREAM 0 in
       let pid = Unix.fork () in
	if pid == (-1) (* fork failure *)
	then
	  bailout "fork() failure!" child_info
	else
	  if pid == 0 (* We are the child - compute our share and exit *)
	then
	  let () = Unix.close fd_read in
	  let s_write = Unix.out_channel_of_descr fd_write in
	  let result = v_work.(nr_process) () in
	  let () = Marshal.to_channel s_write result [] in
	    exit 0
	else
	  (* We are the parent *)
	  let () = Unix.close fd_write in
	  let s_read = Unix.in_channel_of_descr fd_read in
	    setup_childs (1+nr_process) ((s_read,pid)::child_info)
   in
   let all_childs_info = setup_childs 1 [] in
     (* Note that it is important that we start counting at 1 here, as 
the parent will do
        chunk #0!
     *)
   let result_chunk0 = v_work.(0) () in
     (* Note that we just do assume that all pieces of the computation 
take the same time.
        We are not trying to be overly sophisticated, fetching data from 
the fastest
        child first. Also, if we wanted a more powerful tool to compute 
with forked processes,
        we might want to divide the big task in a more fine-grained way 
and hand out sub-tasks
        to processes through a scheduler that takes care of when which 
process finishes
        which sub-task. For now, this is overkill.
     *)
   let rec collect_child_results have child_info_todo =
     match child_info_todo with
       | [] -> have
       | ((s_read,pid)::child_info_todo_next) ->
	  let contrib = Marshal.from_channel s_read in
	  let (returned_pid,status) = Unix.waitpid [] pid in
	    if status <> Unix.WEXITED 0
	    then
	      bailout "Child failure!\n%!" have
	    else
	      collect_child_results
		(fun_combine contrib have)
		child_info_todo_next
   in collect_child_results result_chunk0 all_childs_info
;;


(* ---
(* === Example === *)
let sum_of_inverse_squares =
   compute_uniform_workload_forked
     ~fun_combine:(fun a b -> a+.b)
     (let nr_processes=4 in
      let ranges=split_range nr_processes 1 100000 in
      let work subrange_start subrange_end =
        let () = Printf.printf "PID: %d SUB-RANGE %d - %d\n%!"
	 (Unix.getpid()) subrange_start subrange_end
        in
        let rec walk n sum =
	 if n = subrange_end then sum
	 else walk (1+n) (let fn = float_of_int n in sum +. 1.0/.(fn*.fn))
        in walk subrange_start 0.0
      in
        (Array.init nr_processes
	  (fun n ->
	     let (r_s,r_e) = ranges.(n) in
	       fun () -> work r_s r_e)))
;;

(* This gives: 1.64492406679822967
    The full sum would be pi^2/6 = 1.64493406684822641
*)
--- *)

-- 
best regards,
Thomas Fischbacher
tf@functionality.de

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Richard Jones]

On Wed, May 30, 2007 at 04:42:59AM +0100, Jon Harrop wrote:
> 
> Has anyone implemented a parallel map function in OCaml using Unix forks, 
> pipes and maybe marshalling?
> 
> This seems like an easy way to get concurrency in OCaml...

Don't particularly have any code to show but kind of: at Merjis we did
something like this using both MPI and the Ancient module.  (Not at
the same time).

MPI was used to parallelise a simple log parsing job across a cluster
of machines.  This wasn't very successful as it turned out because I
got bitten by Amdahl's law - the thing that was taking the time was
the serial parsing part of the job.

Second approach was to parse the logfiles overnight into a file-backed
memory heap using Ancient.  Then we used several processes to do the
analysis.  The processes were forked, but accessed the file-backed
shared memory directly (so no pipes).

Rich.

-- 
Richard Jones
Red Hat

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Granicz Adam]

On Wed, 30 May 2007 05:42:59 +0200, Jon Harrop <jon@ffconsultancy.com>  
wrote:

>
> Has anyone implemented a parallel map function in OCaml using Unix forks,
> pipes and maybe marshalling?
>
> This seems like an easy way to get concurrency in OCaml...
>

I am swamped with emails so this may have come up already in this thread,  
but Tomas has a nice parallel list implementation at

http://tomasp.net/blog/fsparallelops.aspx

Cheers,
Adam.

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jon Harrop]

On Wednesday 30 May 2007 17:03:01 Granicz Adam wrote:
> I am swamped with emails so this may have come up already in this thread,
> but Tomas has a nice parallel list implementation at
>
> http://tomasp.net/blog/fsparallelops.aspx

Isn't this written in the wrong language?

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

Fwd: [Caml-list] Faking concurrency using Unix forks and pipes

[Jonathan Bryant]

Oops.  Forgot to CC the list...

Begin forwarded message:

> From: Jonathan Bryant <jtbryant@valdosta.edu>
> Date: May 30, 2007 3:43:50 PM EDT
> To: Erik de Castro Lopo <mle+ocaml@mega-nerd.com>
> Subject: Re: [Caml-list] Faking concurrency using Unix forks and pipes
>
>
> On May 30, 2007, at 3:14 PM, Erik de Castro Lopo wrote:
>
>>
>> To exploit multi-process message-passing style concurrency you  
>> need to
>> fork early before much has been allocated.
>
> What I've always done to get around this is fork a process at the  
> very beginning of the code, and whenever I need to fork a process  
> later, I fork one from that process.  That way almost nothing is in  
> the heap.  I do have worries about the efficiency of this though:  
> when marshaling a closure across a socket to another process, it  
> must marshal all the necessary state as well.  I would imagine this  
> has the potential to get slow if there was much state to marshal  
> (i.e., a closure marshaled referencing a large data structure).
>
> --Jonathan
>
>>
>> Erik
>> -- 
>> -----------------------------------------------------------------
>> Erik de Castro Lopo
>> -----------------------------------------------------------------
>> "... a discussion of C++'s strengths and flaws always sounds
>> like an argument about whether one should face north or east
>> when one is sacrificing one's goat to the rain god."
>> -- Thant Tessman
>>
>> _______________________________________________
>> Caml-list mailing list. Subscription management:
>> http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
>> Archives: http://caml.inria.fr
>> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>> Bug reports: http://caml.inria.fr/bin/caml-bugs
>

Re: Fwd: [Caml-list] Faking concurrency using Unix forks and pipes

[Erik de Castro Lopo]

Jonathan Bryant wrote:

> What I've always done to get around this is fork a process at the  
> very beginning of the code, and whenever I need to fork a process  
> later, I fork one from that process.  That way almost nothing is in  
> the heap.

Yep, that works. Its also probably something that could be built 
into the JoCaml extension.

>  I do have worries about the efficiency of this though:  
> when marshaling a closure across a socket to another process, it  
> must marshal all the necessary state as well.  I would imagine this  
> has the potential to get slow if there was much state to marshal  
> (i.e., a closure marshaled referencing a large data structure).

This is a potential problem. This is like so many language features
that if misused, can lead to huge performance degradations. Knowing
about the problem beforehand allows programmers to avoid it.

Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"If you have an apple and I have  an apple and we  exchange apples then
you and I will still each have  one apple. But  if you have an idea and I
have an idea and we exchange these ideas, then each of us will have two
ideas." -- George Bernard Shaw

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jonathan Bryant]

>
>>  I do have worries about the efficiency of this though:
>> when marshaling a closure across a socket to another process, it
>> must marshal all the necessary state as well.  I would imagine this
>> has the potential to get slow if there was much state to marshal
>> (i.e., a closure marshaled referencing a large data structure).
>
> This is a potential problem. This is like so many language features
> that if misused, can lead to huge performance degradations. Knowing
> about the problem beforehand allows programmers to avoid it.

Just throwing out an idea, so someone who is more familiar with the  
GC/runtime correct me if this can't be done, but what about a smaller  
separate heap in shared memory that is reserved for concurrent data?   
Maybe you could declare a type

stype 'a tree =
| Node of 'a * 'a tree * 'a tree
| Leaf of 'a

that is always allocated in the shared heap, and have a separate GC  
thread that manages that heap.  Could that GC be concurrent without  
affecting the performance of non-concurrent data?

--Jonathan

Re: [Caml-list] Faking concurrency using Unix forks and pipes

[Jon Harrop]

On Wednesday 30 May 2007 21:05:11 Jonathan Bryant wrote:
> Just throwing out an idea, so someone who is more familiar with the
> GC/runtime correct me if this can't be done, but what about a smaller
> separate heap in shared memory that is reserved for concurrent data?
> Maybe you could declare a type
>
> stype 'a tree =
>
> | Node of 'a * 'a tree * 'a tree
> | Leaf of 'a
>
> that is always allocated in the shared heap, and have a separate GC
> thread that manages that heap.  Could that GC be concurrent without
> affecting the performance of non-concurrent data?

The programmer would need to explicitly move data from one heap to another, 
which undermines the high-level nature of a functional programming language. 
You'd be back to C-style memory allocation.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
OCaml for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/?e