Erlang网络多进程模型的实验
April 7th, 2010
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原创文章,转载请注明: 转载自系统技术非业余研究
本文链接地址: Erlang网络多进程模型的实验
在做网络程序的时候我们会经常用到多进程模式. 主进程执行bind调用得到句柄后, 同时fork N个子进程, 把句柄传递给子进程, 多进程同时accept来处理.
这个模型在erlang下很有现实意义的. 在之前的测试中,我们演示了erlang的单处理器模式的威力,最多的时候在单cpu上可以发起40,000个tcp广播包.
但是erlang如何利用这个能力呢? 其实Erlang的port也是靠fork来实现的, 是支持这个能力的, 只不过官方的版本会在fork的时候, 把继承过来的句柄全部关闭.
让我们crack下代码来绕过这个问题.
erts/emulator/sys/unix/sys.c
1513 if(0) /*/*fork路径*/*/ 1514 for (i = opts->use_stdio ? 3 : 5; i < max_files; i++) 1515 (void) close(i); ... 1581 fprintf(stderr, "cracked\n"); /*vfork路径*/ 1582 sprintf(fd_close_range, "%d:%d", opts->use_stdio ? 3 : 5, opts->use_stdio ? 3 : 5);
记得重新make && make install
我们下面的代码演示在主进程把一个tcp句柄传递过去, 然后在子进程中恢复成gen_tcp.
root@nd-desktop:~/otp/test# ls *.erl child.erl test.erl root@ubuntu:~/otp/test# erlc *.erl
root@nd-desktop:~/otp/test# cat test.erl
-module(test). -export([start/0]). start()-> process_flag(trap_exit, true), {ok, Sock} = gen_tcp:listen(0, []), {ok, Handle} = inet:getfd(Sock), Command ="erl -noshell -s child -handle " ++ integer_to_list(Handle), io:format("child command line: ~p~n", [Command]), Child = case (catch open_port({spawn, Command}, [in, {line, 256}])) of {'EXIT', Reason}-> io:format("open child error, reason: ~p~n", [Reason]), halt(1); Port-> Port end, register(?MODULE, self()), io:format("STOP ME: test!stop. ~n",[]), loop(Child), io:format("bye~n",[]). loop(Child)-> receive {Child, {data, Result}} -> io:format("child say: ~p~n", [Result]), loop(Child); stop-> halt(0); Other-> io:format("got msg: ~p~n", [Other]), loop(Child) end.
root@nd-desktop:~/otp/test# cat child.erl
-module(child). -export([start/0]). start()-> {ok, [[HandleArg|_]|_]} = init:get_argument(handle), Handle = list_to_integer(HandleArg), io:format("handle: ~w~n", [Handle]), case gen_tcp:fdopen(Handle, []) of {ok, Socket} -> io:format("got socket ok: ~p~n", [Socket]); _ -> io:format("got socket fail~n", []) end, halt(0).
root@ubuntu:~/otp/test# erl -noshell -s test child command line: "erl -noshell -s child -handle 8" cracked STOP ME: test!stop. child say: {eol,"handle: 8"} child say: {eol,"got socket ok: #Port<0.354>"} got msg: {'EXIT',#Port<0.360>,normal} ^C BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded (v)ersion (k)ill (D)b-tables (d)istribution
Bingo! 成功实现目的!
这里给大家一个思路就是说明fork是可行的, 如果你有这个需求把上面的fork patch做好点就行.
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