Question

我试图学习fork，这是一个简单的程序：

#!/usr/bin/perl
# PRGNAME.pl by Whom
#
#
use strict;
use warnings;

main(@ARGV);

sub main
{
    my @array = qw(1 2 3 4 5 6);
    while ( (my $t = pop @array) ) {
        if (! (my $pid = fork) ) {
                exit if ( $t == 2 );
                for(;;){}
        }
    }
    waitpid(-1, 0);
    message("This is the $PRGNAME exercise file.");
}

sub message
{
    my $m = shift or return;
    print("$m\n");
}

sub error
{
    my $e = shift || 'unkown error';
    print("$0: $e\n");
    exit 0;
}

但在我尝试的shell上ps -fu $LOGNAME | grep [f]ork时，我发现：

  i59tib 28361     1   3 16:20:07 pts/34      6:07 /usr/bin/perl ./fork.pl
  i59tib 28363     1   3 16:20:07 pts/34      6:07 /usr/bin/perl ./fork.pl
  i59tib 28366     1   3 16:20:07 pts/34      6:07 /usr/bin/perl ./fork.pl
  i59tib 28364     1   3 16:20:07 pts/34      6:07 /usr/bin/perl ./fork.pl
  i59tib 28362     1   3 16:20:07 pts/34      6:08 /usr/bin/perl ./fork.pl

在我评论此行exit if ( $t == 2 );

时，其中一个进程已退出，也是其父进程

再次运行ps -fu $LOGNAME | grep [f]ork，我发现：

  i59tib   624   623   1 16:29:11 pts/34      0:04 /usr/bin/perl ./fork.pl
  i59tib   629   623   1 16:29:11 pts/34      0:04 /usr/bin/perl ./fork.pl
  i59tib   628   623   1 16:29:11 pts/34      0:04 /usr/bin/perl ./fork.pl
  i59tib   625   623   1 16:29:11 pts/34      0:04 /usr/bin/perl ./fork.pl
  i59tib   627   623   1 16:29:11 pts/34      0:04 /usr/bin/perl ./fork.pl
  i59tib   626   623   1 16:29:11 pts/34      0:04 /usr/bin/perl ./fork.pl
  i59tib   623  4766   0 16:29:11 pts/34      0:00 /usr/bin/perl ./fork.pl

如何在不退出父级的情况下退出子进程？

Answer 1

如何在不退出父级的情况下退出子进程？

父母退出是因为父母到达了程序的最后，所以告诉父母做某事，什么都行！例如，

1 while waitpid(-1, 0) > 0;

Answer 2

如何在不退出父级的情况下退出子进程？

在这里尝试下面的程序孩子在父母之前去世。

#!/usr/bin/perl
print "i am about to fork\n";
my $pid = fork();
if($pid > 0) {
    my $i = 0;
    while($i<5) {
         print "PARENT--I will be keep on running\n";
         sleep(5);
         $i++;
    }
    print "PARENT-- I m about to dead\n";
} else {
    $i = 0;
    while($i <3) {
        print "CHILD-- I will be dead before than parent\n";
        #exit(0);   you can put exit like this also.
        sleep(2);
        $i++;
    }
    print "CHILD-- I m about to dead\n";
}

以下是示例输出。

i am about to fork
PARENT--I will be keep on running
CHILD-- I will be dead before than parent
CHILD-- I will be dead before than parent
CHILD-- I will be dead before than parent
PARENT--I will be keep on running
CHILD-- I m about to dead
PARENT--I will be keep on running
PARENT--I will be keep on running
PARENT--I will be keep on running
PARENT-- I m about to dead

您也可以使用任何支持的信号。您可以获得不同的信号列表here。您也可以在循环中使用相同的示例代码，但请确保将有一个超级父级，其他将是他们的孩子。

请运行此程序以了解更多相关信息。无论您是否使用退出，总是超级父母将退出。

#!/usr/bin/perl
print "i $$ am about to fork\n";
my @children_pids;
my $n = 3;
for my $i ( 0..($n-1) ) {
    my $pid = fork();
    if($pid > 0) {
        print "i m $$ child of".getppid()."\n";
        push @children_pids, $pid;
    } else {
        print "I $$ is about to dead. I am child of".getppid()."\n";
        exit();
    }
}
waitpid $_, 0 for @children_pids;
print "$$ is finished\n";

我的上述程序系统的典型输出如下。

i 3919 am about to fork
i m 3919 child of3092
I 3920 is about to dead. I am child of3919
i m 3919 child of3092
i m 3919 child of3092
I 3921 is about to dead. I am child of3919
I 3922 is about to dead. I am child of3919
3919 is finished

父母将等待所有孩子退出;然后只有退出。

退出子进程，安全

2 个答案: