循环fork的问题

yybmsrs

for(my $i=0;$i<5;$i++)
{
        print "Current process is $$\n";
        my $pid = fork();
        if(!(defined $pid))
        {
                die "Can not fork a child process!!!\n";
        }
        elsif($pid == 0)
        {
                print "This is child process$\n";
#                exit;
        }
        else
        {
                print "This is parent process$\n";
        }
}

打印如下：

Current process is 26563
This is child process:26564
Current process is 26564
This is child process:26565
Current process is 26565
This is child process:26566
Current process is 26566
This is child process:26567
Current process is 26567
This is child process:26568
This is parent process:26566
Current process is 26566
This is parent process:26563
Current process is 26563
This is parent process:26564
Current process is 26564
This is parent process:26565
Current process is 26565
This is child process:26569
This is child process:26570
Current process is 26570
This is child process:26571
Current process is 26571
This is child process:26572
Current process is 26572
This is child process:26573
Current process is 26573
This is child process:26574
Current process is 26574
This is child process:26575
This is parent process:26567
This is child process:26576
Current process is 26576
This is child process:26577
This is child process:26578
This is parent process:26576
This is parent process:26572
This is parent process:26566
This is parent process:26563
Current process is 26563
This is parent process:26564
Current process is 26564
This is parent process:26570
Current process is 26570
This is parent process:26574
This is child process:26579
Current process is 26579
This is child process:26580
Current process is 26580
This is child process:26581
Current process is 26581
This is child process:26582
Current process is 26582
This is child process:26583
This is child process:26584
This is parent process:26579
Current process is 26579
This is parent process:26563
Current process is 26563
This is parent process:26570
Current process is 26570
This is parent process:26582
This is child process:26586
This is child process:26587
Current process is 26587
This is child process:26588
This is child process:26589
This is parent process:26579
This is parent process:26570
This is parent process:26565
Current process is 26565
This is child process:26590
This is parent process:26565
This is parent process:26571
Current process is 26571
This is child process:26591
This is parent process:26571
This is parent process:26573
Current process is 26573
This is child process:26592
This is child process:26585
This is parent process:26573
This is parent process:26564
Current process is 26564
This is child process:26593
This is parent process:26564
This is parent process:26580
This is parent process:26581
This is parent process:26563
Current process is 26563
This is child process:26594
This is parent process:26563

这段代码会循环的fork进程，子进程也循环fork。如果把exit加上的话就没是我想要的了。

在执行完print "This is child process$\n";后子进程不是已经退出了吗？怎么还fork呢？

yybmsrs

Current process is 28397
This is child process:28398
This is parent process:28397
Current process is 28397
This is child process:28399
This is parent process:28397
加了exit后是这样。

dahe_1984

[root@xinxiang ~]# cat test.pl
#!/usr/bin/perl


for(my $i=0;$i<5;$i++)
{
        print "Current process is $$  .....  $i\n";
        my $pid = fork();
        if(!(defined $pid))
        {
                die "Can not fork a child process!!!\n";
        }
        elsif($pid == 0)
        {
                print "This is child process$$\n";
                exit;
        }
        else
        {
                print "This is parent process$$\n";
        }
}
[root@xinxiang ~]# perl test.pl
Current process is 20793  .....  0
This is child process20794
This is parent process20793
Current process is 20793  .....  1
This is child process20795
This is parent process20793
Current process is 20793  .....  2
This is child process20796
This is parent process20793
Current process is 20793  .....  3
This is child process20797
This is parent process20793
Current process is 20793  .....  4
This is child process20798
This is parent process20793

dahe_1984

[root@xinxiang ~]# cat test.pl
#!/usr/bin/perl


for(my $i=0;$i<5;$i++)
{
        print "Current process is $$  .....  $i\n";
        my $pid = fork();
        if(!(defined $pid))
        {
                die "Can not fork a child process!!!\n";
        }
        elsif($pid == 0)
        {
                print "This is child process$$\n";
                #exit;
        }
        else
        {
                print "This is parent process$$\n";
        }
}
[root@xinxiang ~]# perl test.pl
Current process is 20846  .....  0
This is child process20847
Current process is 20847  .....  1
This is child process20848
Current process is 20848  .....  2
This is parent process20846
Current process is 20846  .....  1
This is child process20849
Current process is 20849  .....  3
This is child process20850
Current process is 20850  .....  2
This is child process20851
Current process is 20851  .....  4
This is child process20852
Current process is 20852  .....  3
This is parent process20847
This is child process20853
Current process is 20847  .....  2
This is child process20854
Current process is 20854  .....  4
This is child process20855
Current process is 20855  .....  3
This is parent process20851
This is parent process20848
Current process is 20848  .....  3
This is child process20856
This is child process20857
Current process is 20857  .....  4
This is child process20858
This is parent process20849
Current process is 20849  .....  4
Current process is 20858  .....  4
This is parent process20854
This is child process20859
This is parent process20852
Current process is 20852  .....  4
This is parent process20849
This is child process20861
This is parent process20858
This is parent process20857
This is child process20862
This is parent process20848
Current process is 20848  .....  4
This is parent process20847
Current process is 20847  .....  3
This is parent process20846
This is child process20860
Current process is 20846  .....  2
This is parent process20848
This is child process20864
Current process is 20864  .....  4
This is child process20865
Current process is 20865  .....  3
This is child process20866
This is child process20867
This is parent process20855
Current process is 20855  .....  4
Current process is 20867  .....  4
This is parent process20864
This is parent process20852
This is child process20868
This is child process20869
This is parent process20847
Current process is 20847  .....  4
This is parent process20867
This is parent process20855
This is parent process20847
This is parent process20865
Current process is 20865  .....  4
This is child process20871
This is parent process20865
This is child process20863
This is child process20870
This is parent process20846
Current process is 20846  .....  3
This is child process20872
Current process is 20872  .....  4
This is child process20873
This is parent process20846
Current process is 20846  .....  4
This is parent process20872
This is parent process20846
This is child process20874
This is parent process20850
Current process is 20850  .....  3
This is child process20875
Current process is 20875  .....  4
This is child process20876
This is parent process20875
[root@xinxiang ~]# This is parent process20850
Current process is 20850  .....  4
This is child process20877
This is parent process20850

dahe_1984

我的理解是如果子进程不退出，子进程和父进程都会调用for语句。

yybmsrs

子进程那部分不是已经结束了吗？还没退出？必须用exit吗？

tommydu

ding~

yybmsrs

再顶下

hotsnow

开始fork之前的环境被复制了.子进程也会进入循环的.
这部分再仔细看看书吧.:wink:

撒哈拉里的鱼

必须exit的。如果想多进程，建议http://search.cpan.org/~dlux/Par ... .7.5/ForkManager.pm