erlang创建100万个进程，每一个进程花费多少时间呢？

　　最近工作需要，需要先测试一下erlang启动进程的时间开销：

　　看了一片博客，感觉挺好的，学习erlang推荐http://www.blogjava.net/yongboy/

　　于是参照他的文章里面的一个部分，（当然erlang程序设计一书的107页也有这个代码），自己着手做了下面的测试，看看erlang 创建100万个进程，每一个进程花费多少时间呢？

　　我的系统是OS X , 8G内存，双核四线程~

　　废话少说，先上代码，在代码中已经做了相关备注：

-module(processes).
-export([max/1]).

max(N) ->
    % Returns the maximum number of simultaneously
    % existing processes at the local node as an integer.
    % This limit can be configured at startup
    % by using the +P command line flag of erl(1).
    Max = erlang:system_info(process_limit),
    io:format("Max=:~p~n", [Max]),
    % 下述statistics函数可用来统计某段代码的执行时间
    % Note that the run-time is the sum of the run-time for
    % all threads in the Erlang run-time system
    % and may therefore be greater than the wall-clock time.
    erlang:statistics(runtime),
    % wall_clock can be used in the same manner as runtime,except
    % that real time is measured as opposed to runtime or CPU time.
    erlang:statistics(wall_clock),
    % 被统计的代码区
    L = for(1, N, fun() -> spawn(fun() -> wait() end) end),
    {_, Time1} = erlang:statistics(runtime),
    {_, Time2} = erlang:statistics(wall_clock),
    % 进程杀死
    lists:foreach(fun(Pid) -> Pid ! die end, L),
    % 判断启动一个进程所需时间（系统时间和消耗的真实时间）
    U1 = Time1 * 1000 / N,
    U2 = Time2 * 1000 / N,
    io:format("process spawn time = ~p(~p) microseconds ~n",
        [U1, U2]).

wait() ->
    receive
        die -> void
    end.

for(_N, _N, F) ->
    [F()];
for(I, N, F) ->
    [F() | for(I + 1, N, F)].    

OliviatekiMac-mini:web_test_practice olivia$ erl

Erlang R15B02 (erts-5.9.2) [source] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false] [dtrace]

Eshell V5.9.2 (abort with ^G)

1> c(processes).

{ok,processes}

2> processes:max(10000000).

Max=:32768

=ERROR REPORT==== 13-May-2013::15:20:47 ===

Too many processes

这说明我的版本默认支持32768个进程，

所以，为了支持更多， 

OliviatekiMac-mini:~ olivia$ cd web_test_practice/

OliviatekiMac-mini:web_test_practice olivia$ erl +P 10240000

Erlang R15B02 (erts-5.9.2) [source] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false] [dtrace]

Eshell V5.9.2  (abort with ^G)

1> c(processes).

{ok,processes}

2> processes:max(1000000).

Max=:10240000

process spawn time = 3.93(4.221) mocroseconds 

ok

3> processes:max(1000000).

Max=:10240000

process spawn time = 3.82(4.067) mocroseconds 

ok

4> processes:max(1000000).

Max=:10240000

process spawn time = 3.79(4.012) mocroseconds 

ok

5> processes:max(1000000).

Max=:10240000

process spawn time = 3.79(4.04) mocroseconds 

ok

6> processes:max(1000000).

Max=:10240000

process spawn time = 3.8(4.058) mocroseconds 

ok

7> processes:max(1000000).

Max=:10240000

process spawn time = 3.81(4.079) mocroseconds 

ok

8> processes:max(1000000).

Max=:10240000

process spawn time = 3.85(4.146) mocroseconds 

ok

9> processes:max(1000000).

Max=:10240000

process spawn time = 3.8(4.091) mocroseconds 

ok

10> processes:max(1000000).

Max=:10240000

process spawn time = 3.84(4.164) mocroseconds 

ok

11> processes:max(1000000).

Max=:10240000

process spawn time = 3.94(4.365) mocroseconds 

ok

也就是说，

创建100万个进程，每一个进程花费3.87微秒(μs)的CPU时间，相当于4.124微秒(μs)的消耗时间(亦即消耗的真实时间),当然在一定量的区间内，其值会在一定范围内波动。要是想知道erlang到底能够并发起多少系统调用，可以参考褚霸这篇博客，http://blog.yufeng.info/archives/18