如何在 Erlang 中实现以下循环？

Question

我有以下伪代码：

for ( int i = 0; i < V ; i++ )
{
  for( int j = 0 ; j < V ; j++ )
  {
    if( ( i != j ) && ( tuple {i,j} belong to E ) )
    {
      R[i] := {i,j};
    }
  }
}

我想使用 erlang.
并行化此代码我如何使用 Erlang 实现相同的目的？ _{我是 Erlang 新手...}

编辑：

我知道下面的代码运行是对 say/2 的同时调用：

-module(pmap).

-export([say/2]).

say(_,0) ->
  io:format("Done ~n");

say(Value,Times) ->
  io:format("Hello ~n"),
  say(Value,Times-1).

start_concurrency(Value1, Value2) ->
  spawn(pmap, say, [Value1, 3]),
  spawn(pmap, say, [Value2, 3]).

但是，我们在这里对函数进行硬编码。那么，假设我要调用 say 1000 次，我需要写 spawn(pmap, say, [Valuex, 3]) 1000 次吗？我可以使用递归，但它不会提供顺序性能吗？

编辑：

我尝试了下面的代码，我的目标是创建 3 个线程，每个线程都想运行一个 say 函数。我想同时运行这3个say功能（请在框中评论以获取更多说明）：

-module(pmap).

-export([say/1,test/1,start_concurrency/1]).

say(0) ->
  io:format("Done ~n");

say(Times) ->
  io:format("Hello ~p ~n",[Times]),
  say(Times-1).

test(0) ->
  spawn(pmap, say, [3]);

test(Times) ->
  spawn(pmap, say, [3]),
  test(Times-1).

start_concurrency(Times) ->
  test(Times).

此代码正确吗？

Answer 1

I want to run these 3 say functions concurrently. Is this code correct?

您可以删除 start_concurrency(N) 函数，因为它什么都不做。相反，您可以直接调用 test(N)。

I aim to create 3 threads

在 erlang 中，您创建 processes。

在 erlang 中，缩进是 4 个空格——而不是 2 个。

不要在函数定义的多个函数子句之间放置空行。

如果您希望看到并发性的实际应用，那么在您运行并发执行的任务中必须有一些等待。例如：

-module(a).
-compile(export_all).

say(0) ->
    io:format("Process ~p finished.~n", [self()]);
say(Times) ->
    timer:sleep(rand:uniform(1000)),  %%perhaps waiting to receive data from an http request
    io:format("Hello ~p from process ~p~n",[Times, self()]),
    say(Times-1).

loop(0) ->
    spawn(a, say, [3]);
loop(Times) ->
    spawn(a, say, [3]),
    loop(Times-1).

在shell:

3> c(a).     
a.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,a}

4> a:loop(3).
<0.84.0>
Hello 3 from process <0.82.0>
Hello 3 from process <0.81.0>
Hello 2 from process <0.82.0>
Hello 3 from process <0.83.0>
Hello 2 from process <0.81.0>
Hello 3 from process <0.84.0>
Hello 2 from process <0.83.0>
Hello 1 from process <0.81.0>
Process <0.81.0> finished.
Hello 1 from process <0.82.0>
Process <0.82.0> finished.
Hello 2 from process <0.84.0>
Hello 1 from process <0.83.0>
Process <0.83.0> finished.
Hello 1 from process <0.84.0>
Process <0.84.0> finished.

5>

如果您运行并发的任务中没有随机等待，则任务将按顺序完成：

-module(a).
-compile(export_all).

say(0) ->
    io:format("Process ~p finished.~n", [self()]);
say(Times) ->
    %%timer:sleep(rand:uniform(1000)),
    io:format("Hello ~p from process ~p~n",[Times, self()]),
    say(Times-1).

loop(0) ->
    spawn(a, say, [3]);
loop(Times) ->
    spawn(a, say, [3]),
    loop(Times-1).

在shell:

5> c(a).     
a.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,a}

6> a:loop(3).
Hello 3 from process <0.91.0>
Hello 3 from process <0.92.0>
Hello 3 from process <0.93.0>
Hello 3 from process <0.94.0>
<0.94.0>
Hello 2 from process <0.91.0>
Hello 2 from process <0.92.0>
Hello 2 from process <0.93.0>
Hello 2 from process <0.94.0>
Hello 1 from process <0.91.0>
Hello 1 from process <0.92.0>
Hello 1 from process <0.93.0>
Hello 1 from process <0.94.0>
Process <0.91.0> finished.
Process <0.92.0> finished.
Process <0.93.0> finished.
Process <0.94.0> finished.

7>

当您运行并发执行的任务中没有随机等待时，并发不会带来任何好处。

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