Error reported when using pmap

Patrice Rault <>
Wed Aug 30 21:36:34 CEST 2006


Hello,

Le mercredi 30 août 2006 à 16:22 +0800, Arbow a écrit :
> Hi All:
>       I am new in Erlang, and try the pmap at
> http://www.erlang.org/ml-archive/erlang-questions/200606/msg00187.html:
> 
> In file test.erl:
> -module(test).
> -export([pmap/2]).
> 
> pmap(F, L) ->
>     S = self(),
>     Pids = list:map(
>                     fun(I) -> 
>                         spawn(
>                               fun() -> 
>                                   do_f(S, F, I) 
>                               end) 
>                     end, L),
>     gather(Pids).
> 
> gather([H|T]) ->
>     receive
>         {H, Ret} -> [Ret|gather(T)] 
>     end;
> gather([]) ->
>     [].
> 
> do_f(Parent, F, I) ->
>     io:format("Receive item ~w~n", [I]),
>     Parent ! {self(), (catch F(I))}.
> 
> In file testmain.erl:
> -module(testmain).
> -export([test3/0]).
> 
> test3() ->
>     MyList = [1,2,3,4,5,6,7,8,9,10],
>     lists:map(fun(I) -> I*2 end, MyList).
> 
> when I execute " testmain:test3(). ", I get errors:
> 
> =ERROR REPORT==== 30-Aug-2006::16:21:51 === 
> Error in process <0.36.0> on node '' with exit
> value:
> {undef,[{testmain,test3,[]},{erl_eval,do_apply,5},{shell,exprs,6},{shell,eval_loop,3}]}
> 
> ** exited: {undef,[{testmain,test3,[]},
>                    {erl_eval,do_apply,5},
>                    {shell,exprs,6},
>                    {shell,eval_loop,3}]} **
> 
> Anyone could help me? Thanks.
> 
> Best regards.
> Arbow

Try this

-module(test_pmap).
-export([pmap/2]). 

pmap(F, L) ->
    S = self(),
    Pids = lists:map(               % list:map ?? 
                    fun(I) -> 
                        spawn(
                              fun() -> 
                                  do_f(S, F, I) 
                              end) 
                    end, L),
    gather(Pids).

gather([H|T]) ->
    receive
        {H, Ret} -> [Ret|gather(T)] 
    end;
gather([]) ->
    [].

do_f(Parent, F, I) ->
    %io:format("Receive item ~w~n", [I]),
    Parent ! {self(), (catch F(I))}.

-module(testmain).
-export([test3/0]).

test3() ->
    MyList = [1,2,3,4,5,6,7,8,9,10],
    %lists:map(fun(I) -> I*2 end, MyList),      
    test_pmap:pmap(fun(I) -> I*2 end, MyList).

Erlang (BEAM) emulator version 5.5 [source] [async-threads:0] [hipe]

Eshell V5.5  (abort with ^G)
1> c(test_pmap).
{ok,test_pmap}
2> c(testmain).
{ok,testmain}
3> testmain:test3().
[2,4,6,8,10,12,14,16,18,20]
4> l(testmain).
{module,testmain}
5>

Regards.





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