サブプロセスをforkしたい

とりあえず#perl6で聞いてみた

13:10:05 >#perl6@freenode:lopnor< is there any way to fork a process?
13:11:41 <#perl6@freenode:TiMBuS> yes, if you use zavolaj you can call fork
13:11:56 <#perl6@freenode:TiMBuS> https://github.com/jnthn/zavolaj
13:12:02 >#perl6@freenode:lopnor< is it core in rakudo star?
13:12:29 <#perl6@freenode:TiMBuS> not sure, but it's a simple single .pm file you can include
13:12:52 <#perl6@freenode:TiMBuS> https://github.com/jnthn/zavolaj/blob/master/examples/unix-fork.p6 there's the example
13:13:20 >#perl6@freenode:lopnor< oh, it's very easy!
13:13:34 >#perl6@freenode:lopnor< thank you, i will try that
13:13:36 <#perl6@freenode:TiMBuS> yeah i was surprised at how easy it was, as well
13:14:00 <#perl6@freenode:TiMBuS> im not sure if it's very efficient. keep an eye on your memory usage
13:14:55 >#perl6@freenode:lopnor< i wanted to fork for testing some server,
13:15:03 >#perl6@freenode:lopnor< so it should be okay for me
13:27:40 >#perl6@freenode:lopnor< TiMBuS: hm, the sample doesn't work in my mac,
13:27:55 >#perl6@freenode:lopnor< saying "Could not locate symbol 'fork' in native library '(resident)'"
13:28:33 >#perl6@freenode:lopnor< i'm using rakudo star 2010-11
13:29:15 <#perl6@freenode:TiMBuS> you might need to specify the library name
13:30:24 >#perl6@freenode:lopnor< what library name?
13:32:31 <#perl6@freenode:TiMBuS> erm, whats fork in osx?
13:32:43 <#perl6@freenode:TiMBuS> 'libc' ?
13:32:56 >#perl6@freenode:lopnor< ah,
13:33:23 >#perl6@freenode:lopnor< sub fork() returns Int is native() { ... } 
13:33:28 >#perl6@freenode:lopnor< this line should be
13:33:54 >#perl6@freenode:lopnor< "sub fork() returns Int is native(libc) { ... }" or something,
13:33:59 >#perl6@freenode:lopnor< right?
13:34:07 <#perl6@freenode:TiMBuS> yeah
13:34:31 <#perl6@freenode:TiMBuS> its a string, so  is native('libc')
13:34:51 >#perl6@freenode:lopnor< thank you!
13:34:56 >#perl6@freenode:lopnor< it ran
13:40:18 <#perl6@freenode:sorear> is native<libc>
13:41:23 >#perl6@freenode:lopnor< it also ran:)

ということで一発で教えてもらえました。

使ってみよう

いま個人的に進めているplackdoというプロジェクトの中で書いたテストです。ソースはこちらです。

use Test;
use NativeCall;
use LWP::Simple;
use Plackdo::Handler::Standalone;

ok 1;

sub fork returns Int is native<libc> { ... }

my $pid = fork();
if ($pid) {
    is LWP::Simple.get('http://localhost:5000/'), 'Hello, World';
} else {
    my $handler = Plackdo::Handler::Standalone.new;
    $handler.run(sub (%env){
        return [
            200,
            [
                Content-Type => 'text/plain',
                Content-Length => '12',
            ],
            ['Hello, World']
        ];
    });
}
run("kill $pid");

done_testing;

# vim: ft=perl6 :

zavolajはrakudo-star-2010-11に同梱されていたので、追加のインストールは不要でした。

use NativeCall;
sub fork returns Int is native<libc> { ... }

これでfork()するとlibcのforkが呼ばれるようになります。実運用的にはこのsub forkを記述したモジュールを書いて使い回すのが現実的だと思います。そして、呼び出す側は

my $pid = fork();
if ($pid) {
# parent process
    # do something
    run("kill $pid"); # kill the child
} else {
# child process
}

こんな感じで、perl5とおんなじ感じです。

「perl6にはforkがない.......」そんなふうに考えていた時期が俺にもありました。

enjoy!