请教：deathcult！父进程与子进程communicate

yxzjf

看了你的关于：父进程与子进程communicate..利用PIPE的例子(perl原创精华文章！)
由于水平有限，逻辑思路我也没有理清楚！
能否详细说明一下，谢谢！

1. 
   
2. #!/usr/bin/perl
   
3. use strict;
   
4. use IO::Select;
   
5. use POSIX qw(WNOHANG);
   
6. 
   
7. #---Define constants：定义准备先fork几个Process
   
8. use constant PREFORK_CHILDREN   =>; 3;
   
9. # debugging information：显示过程
   
10. use constant DEBUG              =>; 1;
    
11. 
    
12. # declare globals
    
13. my $DONE=0;             # set flag to true when server done
    
14. my %STATUS = ();        #child status information, child pid form keys of the ha
    
15. sh, status form the values
    
16. #--- 纪录所有Child Process的id...
    
17. my %CHILDREN = ();
    
18. #---Interrupt handles,跳出loop
    
19. $SIG{TERM} = $SIG{INT}=$SIG{HUP} = sub { $DONE++ };
    
20. #--- get CHLD Signal
    
21. $SIG{CHLD} = sub {
    
22.          while((my $child=waitpid(-1,WNOHANG)) >; 0){
    
23.            delete $CHILDREN{$child};
    
24.          }
    
25.       };
    
26. # create a pipe for IPC：建立PIPE
    
27. pipe(CHILD_READ,CHILD_WRITE) or die "Can't make pipe!\n";
    
28. my $IN = IO::Select->;new(\*CHILD_READ);
    
29. # prefork some children
    
30. make_new_child() for (1..PREFORK_CHILDREN);
    
31. 
    
32. # main loop
    
33. while(!$DONE){
    
34.   # avoid parent block in the I/O call
    
35.   if ($IN->;can_read){ # got a message from one of the children
    
36.     my $message;
    
37.     next unless sysread(CHILD_READ,$message,4096);
    
38.   # may contain several messages
    
39.     my @messages = split "\n",$message;
    
40.   # retrive every pid and status code
    
41.     foreach (@messages){
    
42.       next unless my ($pid,$status) = /^(\d+) (.+)$/;
    
43.   # change status
    
44.       if($status ne "done"){
    
45.          $STATUS{$pid} = $status;
    
46.       }else{
    
47.   # delete pid
    
48.          delete $STATUS{$pid};
    
49.       }
    
50.     }
    
51.   }
    
52. 
    
53.   warn join(' ',map {"$_=>;$STATUS{$_}"} keys %STATUS),"\n" if DEBUG;
    
54.   last unless %CHILDREN
    
55. }
    
56. warn "Termination received, killing children\n" if DEBUG;
    
57. #-------------杀掉所有Child Process
    
58. kill TERM =>; keys %CHILDREN;
    
59. sleep while %CHILDREN;
    
60. 
    
61. warn "Normal termination.\n";
    
62. exit 0;
    
63. #---- 建立新的Process
    
64. sub make_new_child{
    
65.   die "can't fork :$!" unless(defined( my $child = fork()));
    
66.   if($child){   # child >; 0, so we're the parent
    
67.     $CHILDREN{$child} = 1;
    
68.     warn "launching child $child\n" if DEBUG;
    
69.   }else{
    
70.     close CHILD_READ;   # no need to read from pipe
    
71.     do_child();         # child handles incoming connections
    
72.     exit 0;             # child is done
    
73.   }
    
74. }
    
75. #------ child process
    
76. sub do_child{
    
77.    # write status code: idle
    
78.    syswrite CHILD_WRITE,"$$ idle\n";
    
79.    for(1..1000000){ };
    
80.    syswrite CHILD_WRITE,"$$ busy\n";
    
81.    for(1..1000000){ };
    
82.    syswrite CHILD_WRITE,"$$ done\n";
    
83. }
    

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