#!/usr/local/bin/perl

$mode = shift;

if ( $mode eq 'flock' ){
} elsif ( $mode eq 'symlink' ){
    $lockfile = "sym-lock";
    unlink($lockfile);
} elsif ( $mode eq 'mkdir' ){
    $lockdir = "mkdir-lock";
    rmdir($lockfile);
} else {
    die "You must specify mode `flock', `symlink' or `mkdir'\n";
}

$counter_file = "$mode.txt";
$countup_func = "countup_$mode";
open(F,">$counter_file");
print F "0\n";
close(F);

$loop = shift || 1000;        # カウントアップする数
$max_children = shift || 5;  # 同時に生成する子供の数
$now_children = 0;            # 現在の子供の数

for ( $x=0 ; $x<$loop ; $x++ ){
    if ( $pid = fork() ){  # 親
	$now_children++;
    } else {               # 子
	&$countup_func($x);
	exit;
    }
    if ( ! $pid ){              # fork できなかった
	die "Cannot fork! $!";
    }
    if ( $now_children == $max_children ){  # 制限以上のプロセスを作らない
	wait;
	$now_children--;
    }
}

while ($now_children){  # 最後に残った子供たちを待つ
    wait;
    $now_children--;
}

open(F,$counter_file);   # 結果表示
printf "Result ($counter_file) =%s",scalar(<F>);
close(F);

exit;


#--------------------- flock を使ったカウントアップ

sub countup_flock {
    ($child_number) = @_;
    open(F, "+< $counter_file");
    flock(F,2);
    $num=<F>;
    seek(F, 0, 0);
    printf F "%d\n",$num+1;
    close(F);

    printf "$mode: I'm %dth child. counter=%d\n",$child_number+1,$num+1;
}


#---------------------- symlink を使ったカウントアップ

sub countup_symlink {
    ($child_number) = @_;
    $lock_flg = 0;
    while (1){	
	$lock_flg = symlink("$$",$lockfile);
	last if ( $lock_flg );
	select(undef,undef,undef,0.1);  # 0.1 秒 sleep
    }
    open(F,"$counter_file");
    $num=<F>;
    close(F);
    
    open(F,">$counter_file");
    printf F "%d\n",$num+1;
    close(F);

    printf "$mode: I'm %dth child. counter=%d\n",$child_number+1,$num+1;
    unlink($lockfile);
}


#-------------------- mkdir を使ったカウントアップ

sub countup_mkdir {
    ($child_number) = @_;
    $lock_flg = 0;

    while (1){	
	$lock_flg = mkdir($lockdir,0777);
	last if ( $lock_flg );
	select(undef,undef,undef,0.1);  # 0.1 秒 sleep
    }
    open(F,"$counter_file");
    $num=<F>;
    close(F);
    
    open(F,">$counter_file");
    printf F "%d\n",$num+1;
    close(F);

    printf "$mode: I'm %dth child. counter=%d\n",$child_number+1,$num+1;
    rmdir($lockdir);
}