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 <[email protected]>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 > > > > > > > -- > Caml-list mailing list. Subscription management and archives: > https://sympa-roc.inria.fr/wws/info/caml-list > 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 and archives: https://sympa-roc.inria.fr/wws/info/caml-list Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
