关于理解Perl的fork函数的一个范例

方便理解，Perl的fork函数派生子进程的过程：

#!/usr/bin/perl -w
# wangxiaoyu#live.com
use strict;

defined(my $pid=fork()) or die "Fork process failured:$!\n";
unless($pid)
{
# This is the child process.
system "date";
sleep(3);
print ("Exit child after 3 seconds wait!\n");
exit();
}
# This is the parent process.
waitpid($pid,0);
system "date";
print ("exit parent!\n");

程序执行结果如下：

# perl perl-fork02.pl

Wed Aug 4 22:51:38 HKT 2010

Exit child after 3 seconds wait!

Wed Aug 4 22:51:41 HKT 2010

exit parent!

#

如果不在父进程中提供waitpid函数的话，父进程会在成功创建子进程后不等待子进程执行完毕，立即执行其余的代码，这样的话执行的结果如下：

# perl perl-fork02.pl

Wed Aug 4 22:50:25 HKT 2010

Wed Aug 4 22:50:25 HKT 2010

exit parent!

# Exit child after 3 seconds wait!