进程太多，为什么？

Question

我正在尝试的问题是

Write a ring benchmark. Create N processes in a ring. Send a message round the ring M times so that a total of N * M messages get sent. Time how long this takes for different values of N and M.

我的尝试看起来像

-module(ring).
-author("harith").

%% API
-export([message/2, test/0]).

test() ->
  Max = erlang:system_info(process_limit),
  io:format("max processes: ~p~n", [Max]),
  Time = [timer:tc(ring, message, [N, M]) || N <- lists:seq(10, 500, 10), M <- lists:seq(1000, 100000, 1000)],
  [io:format("(~p)processes, (~p) messages, (~p) microseconds~n", [N, M, T]) || {T, {N, M}} <- Time].

% create ring of N processes and
% send M messages between them
message(N, M) when is_integer(N), is_integer(M), N > 0, M > 0 ->
  Ring = create_ring(N),
  [Start | T] = Ring,
  Start ! {T, Ring, 1, M},
  {N, M}.

create_ring(N) ->
  Processes = [spawn(fun() -> loop() end) || _ <- lists:seq(1, N)],
  [H | _] = Processes,
  lists:append(Processes, [H]).

loop() ->
  receive
    {[H | T], _L, CurrentMessage, M} ->
      % io:format("~p received ~p~n", [self(), CurrentMessage]),
      H ! {T, _L, CurrentMessage, M},
      loop();
    {[], Ring, CurrentMessage, M} ->
      % io:format("~p received ~p with empty list~n", [self(), CurrentMessage]),
      case CurrentMessage < M of
        true ->
          [_ | [Next | T]] = Ring,
          NewMessage = CurrentMessage + 1,
          % io:format("sending message ~p to ~p~n", [NewMessage, Next]),
          Next ! {T, Ring, NewMessage, M};
        false -> void %io:format("done sending ~p messages in ~p ring, taking rest now.~n", [M, Ring])
      end,
      loop()
  end.

有问题吗？
当我测试此代码时，它失败并出现以下错误

1> c(ring).
{ok,ring}
2> ring:test().
max processes: 262144

=ERROR REPORT==== 11-Jan-2015::12:59:24 ===
Too many processes

** exception error: a system limit has been reached
     in function  spawn/3
        called as spawn(erlang,apply,[#Fun<ring.0.102056517>,[]])
     in call from spawn/1 
     in call from ring:'-create_ring/1-lc$^0/1-0-'/1 (ring.erl, line 30)
     in call from ring:'-create_ring/1-lc$^0/1-0-'/1 (ring.erl, line 30)
     in call from ring:create_ring/1 (ring.erl, line 30)
     in call from ring:message/2 (ring.erl, line 24)
     in call from timer:tc/3 (timer.erl, line 194)
     in call from ring:'-test/0-lc$^1/1-1-'/3 (ring.erl, line 18)
*** ERROR: Shell process terminated! ***

=ERROR REPORT==== 11-Jan-2015::12:59:24 ===
Too many processes


=ERROR REPORT==== 11-Jan-2015::12:59:24 ===
Error in process <0.26.0> with exit value: {system_limit,[{erlang,spawn_link,[erlang,apply,[#Fun<shell.1.95205691>,[]]],[]},{erlang,spawn_link,1,[]},{shell,get_command,5,[{file,"shell.erl"},{line,298}]},{shell,server_loop,7,[{file,"shell.erl"},{line,229}]}]}

Eshell V6.2  (abort with ^G)
*** ERROR: Shell process terminated! ***

=ERROR REPORT==== 11-Jan-2015::12:59:25 ===
Too many processes


=ERROR REPORT==== 11-Jan-2015::12:59:25 ===
Error in process <0.32.16> with exit value: {system_limit,[{erlang,spawn_link,[erlang,apply,[#Fun<shell.1.95205691>,[]]],[]},{erlang,spawn_link,1,[]},{shell,get_command,5,[{file,"shell.erl"},{line,298}]},{shell,server_loop,7,[{file,"shell.erl"},{line,229}]}]}


User switch command
 -->

嗯，我的数学不是很好，但我还是做了下面的数学，看看是否真的是这样。
我试图查看我的程序正在创建多少个进程，这直接将我链接到 N 是什么

Time = [timer:tc(ring, message, [N, M]) || N <- lists:seq(10, 500, 10), M <- lists:seq(1000, 100000, 1000)],

我试图从

中找出整数的总和

10, 20, 30, ...., 500

相差 10

我试着找出 n = number of terms 的顺序为

对于 a1 = 10, an = 500, d = 10

结果是 n=50

我发现总和为

结果是 (10 + 500)*50/2 12750 并且根据日志可以创建的最大进程数

max processes: 262144

有人可以帮助我理解这个问题吗？

谢谢

Answer 1

你的数字 12750 是正确的。但是你在这个列表理解中调用 ring:message/2:

[timer:tc(ring, message, [N, M]) || N <- lists:seq(10, 500, 10), M <- lists:seq(1000, 100000, 1000)]

将其修改为不执行任何操作并计算其长度，然后将该长度乘以 12750 得到：

1> length([x || N <- lists:seq(10, 500, 10), M <- lists:seq(1000, 100000, 1000)]).
5000
2> 12750*5000.
63750000

这当然远高于默认的最大进程限制 262144。

进程太多，为什么？

Too many processes, why?

erlang