perl多进程数量控制－信号或者判断pid是否存在

实例的功能就是多进程ping不同的主机，查看主机是否可连通。。试了一把。

1.通过子进程返回的CHLD信号

#!/usr/bin/perl -w
use Net::Ping;
use POSIX;
my @ip;
open IN,'ip.txt' or die'error';
 @ip=<IN>;
close(IN);
my $total=$#ip+1;
my $num=$total;
my $a=0;
my $bam=0;
$SIG{CHLD}=sub{$a--;$bam++};
my %pid;
while($total)
{
 if($a<5)
  {
   my $pid=fork();
   $pid{$pid}=1;
   if($pid == 0)
    {
      my $p=Net::Ping->new();
      my $de=$num-$total;
      $ip[$de]=~s/\n//g;
      if($p->ping($ip[$de],5))
       {
          print "$ip[$de] is reachable\n";
        }
      else{
          print "$ip[$de] is noreach\n";
       }
      $p->close();
      exit 0;
    }
   $a++;
   $total--;
   }
  while($bam >0)
   {
     while(my $exit_pid=waitpid(-1,WNOHANG) > 0)
      {
        $bam--;
        if(exists($pid{$exit_pid})){delete $pid{$exit_pid};}
      }
   }
}

my @left=keys %pid;
if(@left)
 {
   foreach my $j(@left)
    {
        waitpid($j,0);
    }
 }
 

2. 通过判断子进程的pid是否存在

  #!/usr/bin/perl -w
use Net::Ping;
use POSIX;

$SIG{CHLD}='IGNORE';
my @ip;
open IN,'ip.txt' or die'error';
 @ip=<IN>;
close(IN);
my $total=$#ip+1;

my $i;
my %pid;
for($i=0;$i<$total;$i++)
 {
    my @pids=keys %pid;
    while($#pids >=4)
     {
          foreach my $j(@pids)
           {
              delete $pid{$j} unless(kill 0 =>$j);
           }
         @pids=keys %pid;
     }
   my $pid=fork();
   if($pid)
     {
          $pid{$pid}=1;
     }
  else{
       my $p=Net::Ping->new();
       $ip[$i]=~s/\n//g;
      if($p->ping($ip[$i],5))
       {
          print "$ip[$i] is reachable\n";
       }
      else{
          print "$ip[$i] is noreach\n";
       }
      $p->close();
      exit 0;
      }
 }

my @left=keys %pid;
while($#left != -1)
 {
   foreach my $k(@left)
   {
      delete $pid{$k} unless(kill 0 =>$k);
   }
  @left=keys %pid;
}