Re: [Caml-list] [ANN]: Parmap

[Roberto Di Cosmo <roberto@dicosmo.org>]

Dear Ashish,
	thanks for the report; these issues are fixed in the latest
commit on https://gitorious.org/parmap  (bfdf714)

Let me know if you find any more issues

All the best

--Roberto

On Wed, Aug 17, 2011 at 03:25:53PM -0400, Ashish Agarwal wrote:
> Thanks. This is very exciting. I tried a simple test but get an error:
> 
> # #require "extlib";;
> # #require "parmap";;
> # Parmap.parfold (+) (List.of_enum (1 -- 1000)) 0 ~ncores:1;;
> Signal -10
> 
> The function List.of_enum is from Batteries. I use it just to create a long
> list of integers.
> 
> Also, you need to add extlib to the META file.
> 
> 
> 
> On Wed, Aug 17, 2011 at 1:10 PM, Roberto Di Cosmo <roberto@dicosmo.org> wrote:
> 
>     Dear all,
>           a few lines to announce the availability of a minimalistic library
>     which
>     can be useful to exploit your multicore processor with minimal
>     modifications to
>     your OCaml programs.
> 
>     In a nutshell
>     -------------
> 
>     If you want to use your many cores to accelerate an operation which happens
>     to
>     be a map, fold or map/fold (map-reduce), just use Parmap's parmap, parfold
>     and
>     parmapfold primitives in place of the standard List.map and friends, and
>     specify
>     the number of subprocesses to use by the optional parameter ncores.
> 
>     For example, in the classical Mandelbrot example present in the example
>     directory,
>     the line
> 
>            Parmap.parmap pixel tasks ~ncores:i
> 
>     allows to spawn i separate processes, each working on 1/ith of the list
>     tasks.
> 
>     Rationale
>     ---------
> 
>     The principle of Parmap is very simple: when you call one of the three
>     available
>     primitives, map, fold, and  mapfold , your OCaml  sequential program forks
>      in n
>     subprocesses (you choose the n), and each subprocess performs the
>     computation on
>     the  1/n of the data, returing  the results through a  shared memory area
>     to the
>     parent process, that resumes  execution once all  the children  have
>     terminated,
>     and the data has been recollected.
> 
>     This means that you *must* run your program on a *single* multicore
>     machine.
>     Repeat after us: Parmap is not meant to run on a cluster, see one of the
>     many
>     available (re)implementations of the map-reduce schema for that.
> 
>     By forking the parent process  on a sigle  machine, the children get
>     access, for
>     free, to all the data structures already built, even the imperative ones,
>     and as
>     far as your computation  inside the map/fold  does not produce side effects
>     that
>     need  to be  preserved, the  final result will   be the same  as  
>     performing the
>     sequential operation, the only difference is that you might get it faster.
> 
>     Of course, if you happen  to have open  channels, or files, or other
>     connections
>     that should only be  used by the parent  process, your program  may behave
>     in  a
>     very wierd way: as an example, *do  not* open a  graphic window before
>     calling a
>     Parmap primitive, and   *do   not*  use  this  library   if  your  program
>        is
>     multi-threaded!
> 
>     The OCaml code is quite simple and does not rely on any  external C
>     library: all
>     the magic is done by your operating system's fork and memory mapping
>     mechanisms.
>     One could gain some speed by implementing a marshal/unmarshal operation
>     directly
>     on bigarrays, but we did not do this yet.
> 
> 
>     How to get it
>     -------------
> 
>     Project home: https://gitorious.org/parmap
> 
>     To compile and install:
> 
>      git clone git://gitorious.org/parmap/parmap.git
>      make
>      make install
> 
>     Enjoy
> 
>     -- Marco Danelutto and Roberto Di Cosmo
> 
>     P.S.: special thanks to Pierre Chambart for useful discussions on this code
> 
> 
> 
> 
> 
> 
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> 
> 
> 

-- 
--Roberto Di Cosmo
 
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