在Erlang中获取生成函数的结果 [英] Getting result of a spawned function in Erlang

问题描述

我目前的目标是写Erlang代码来计算N个元素的列表，其中每个元素是它的索引的阶乘（因此，对于N = 10，我想得到[1 !, 2！ 3 !, ...，10！]）。更重要的是，我希望在一个单独的过程中计算每一个元素（我知道这样做效率很低，但是我预计会实现它，并将其效率与其他方法进行比较）。

在我的代码中，我想使用一个函数作为给定N的循环，N，N-1，N-2 ...产生一个计算阶乘（N）的过程，并发送导致一些收集功能，将接收到的结果打包到列表中。我知道我的概念可能是过于复杂的，所以希望代码会更多解释一下：

  messageFactorial（N，listPID） - > ; 
 listPID！阶乘（N）。 %%将计算的阶乘发送到收藏家。 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% 
 nProcessesFactorialList（-1） - > 
 ok; 
 nProcessesFactorialList（N） - > 
 spawn（pFactorial，messageFactorial，[N，listPID]），每个N个生成的%% ... 
 nProcessesFactorialList（N-1）。 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 listPrepare（List） - > %%collector，对于最后一个阶乘返回
接收%%一个阶乘列表（1！= 1）。 
 1  - >清单; 
 X  - > 
 listPrepare（[X | List]）
 end。 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% ％
 startProcessesFactorialList（N） - > 
 register（listPID，spawn（pFactorial，listPrepare，[[]]）），
 nProcessesFactorialList（N）。 
  

我想这将工作，我的意思是listPrepare终于返回一个阶乘列表。但问题是，我不知道如何得到这个列表，如何得到它返回的？至于现在我的代码返回ok，因为这是nProcessesFactorialList在其完成时返回的。我想到最后将listPrepare的结果列表发送到nProcessesFactorialList，但是它也需要是一个已注册的进程，我不知道如何恢复该列表。

所以基本上，如何从一个注册进程运行listPrepare（这是我的列表）获得结果？如果我的代码根本不对，我会问一个如何更好的建议。感谢提前。

解决方案

我的方式如何做这种任务是

  -module（par_fact）。 
 
 -export（[calc / 1]）。 
 
 fact（X） - >事实（X，1）。 
 
 fact（0，R） - > R等
事实（X，R）当X> 0  - >事实（X-1，R * X）。 
 
 calc（N） - > 
 Self = self（），
 Pids = [spawn_link（fun（） - > Self！{self（），{X，fact（X）}} end）
 || X <列表：seq（1，N）]，
 [receive {Pid，R}  - > R end || Pid<  -  Pids]。 
  

结果：

 > par_fact：计算值（25）。 
 [{1,1}，
 {2,2}，
 {3,6}，
 {4,24}，
 {5,120}，
 {6,720}，
 {7,5040}，
 {8,40320}，
 {9,362880}，
 {10,3628800}，
 {11,39916800}，
 {12,479001600}，
 {13,6227020800}，
 {14,87178291200}，
 {15,1307674368000}，
 {16,20922789888000}，
 {17,355687428096000}，
 {18,6402373705728000}，
 {19,121645100408832000}，
 {20,2432902008176640000}，
 {21,51090942171709440000}，
 {22,1124000727777607680000}，
 {23,25852016738884976640000}，
 {24,620448401733239439360000}，
 {25,15511210043330985984000000}] 
  

My objective at the moment is to write Erlang code calculating a list of N elements, where each element is a factorial of it's "index" (so, for N = 10 I would like to get [1!, 2!, 3!, ..., 10!]). What's more, I would like every element to be calculated in a seperate process (I know it is simply inefficient, but I am expected to implement it and compare its efficiency with other methods later).

In my code, I wanted to use one function as a "loop" over given N, that for N, N-1, N-2... spawns a process which calculates factorial(N) and sends the result to some "collecting" function, which packs received results into a list. I know my concept is probably overcomplicated, so hopefully the code will explain a bit more:

messageFactorial(N, listPID) ->
    listPID ! factorial(N).      %% send calculated factorial to "collector".

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
nProcessesFactorialList(-1) ->
    ok;
nProcessesFactorialList(N) ->
    spawn(pFactorial, messageFactorial, [N, listPID]),   %%for each N spawn...
    nProcessesFactorialList(N-1).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
listPrepare(List) ->            %% "collector", for the last factorial returns
    receive                     %% a list of factorials (1! = 1).
        1 -> List;
        X ->
            listPrepare([X | List])
    end.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
startProcessesFactorialList(N) ->
    register(listPID, spawn(pFactorial, listPrepare, [[]])),
    nProcessesFactorialList(N).

I guess it shall work, by which I mean that listPrepare finally returns a list of factorials. But the problem is, I do not know how to get that list, how to get what it returned? As for now my code returns ok, as this is what nProcessesFactorialList returns at its finish. I thought about sending the List of results from listPrepare to nProcessesFactorialList in the end, but then it would also need to be a registered process, from which I wouldn't know how to recover that list.

So basically, how to get the result from a registered process running listPrepare (which is my list of factorials)? If my code is not right at all, I would ask for a suggestion of how to get it better. Thanks in advance.

解决方案

My way how to do this sort of tasks is

-module(par_fact).

-export([calc/1]).

fact(X) -> fact(X, 1).

fact(0, R) -> R;
fact(X, R) when X > 0 -> fact(X-1, R*X).

calc(N) ->
    Self = self(),
    Pids = [ spawn_link(fun() -> Self ! {self(), {X, fact(X)}} end)
            || X <- lists:seq(1, N) ],
    [ receive {Pid, R} -> R end || Pid <- Pids ].

and result:

> par_fact:calc(25).
[{1,1},
 {2,2},
 {3,6},
 {4,24},
 {5,120},
 {6,720},
 {7,5040},
 {8,40320},
 {9,362880},
 {10,3628800},
 {11,39916800},
 {12,479001600},
 {13,6227020800},
 {14,87178291200},
 {15,1307674368000},
 {16,20922789888000},
 {17,355687428096000},
 {18,6402373705728000},
 {19,121645100408832000},
 {20,2432902008176640000},
 {21,51090942171709440000},
 {22,1124000727777607680000},
 {23,25852016738884976640000},
 {24,620448401733239439360000},
 {25,15511210043330985984000000}]

这篇关于在Erlang中获取生成函数的结果的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！