Perl脚本用pipe进行父进程与子进程通信的问题

ksfblc

代码1是问题，其功能就是实现父进程与子进程之间的双向通信。流程如下：
child向parent发送消息1。
parent接收到后向child发送消息1。
child接收到后向parent发送消息2。
parent接收到后向child发送消息2。
child接收到后向parent发送消息3。
parent接收到后向child发送消息3。
child接收到后向parent发送消息4。
parent接收到后向child发送消息OVER，并退出循环。
child接收到后退出循环。

代码1的问题是，parent在第一次接收消息是时候就卡不动了，应该是没有接收到消息。

对代码稍做调整，形成代码2，问题就解决了。所做的调整在所有发送的消息后面加上"\n"。但是其中的原因是什么呢？大家帮忙分析分析。


代码1：

1. pipe(ParentREADER, ChildWRITER);
   
2. pipe(ChildREADER, ParentWRITER);
   
3. $retval = fork();
   
4. if ($retval != 0) {
   
5. close (ChildREADER);
   
6. close (ChildWRITER);
   
7. select ParentWRITER;
   
8. $| = 1;
   
9. while (1)
   
10. {
    
11. print STDOUT "Parent Prepare to RECIEVER\n";
    
12. sleep 1;
    
13. $RECIEVER = <ParentREADER>;
    
14. print STDOUT "Parent RECIEVER $RECIEVER\n";
    
15. if ($RECIEVER eq "4")
    
16. {
    
17. print STDOUT "Parent Over\n";
    
18. print ParentWRITER "OVER";
    
19. last;
    
20. }
    
21. else
    
22. {
    
23. print ParentWRITER "$RECIEVER";
    
24. }
    
25. }
    
26. }
    
27. else {
    
28. close (ParentWRITER);
    
29. close (ParentWRITER);
    
30. select ChildWRITER;
    
31. $| = 1;
    
32. $WRITER = 1;
    
33. print STDOUT "Child WRITER $WRITER\n";
    
34. print ChildWRITER "$WRITER";
    
35. while (1)
    
36. {
    
37. print STDOUT "Child Prepare to RECIEVER\n";
    
38. $RECIEVER = <ChildREADER>;
    
39. if ($RECIEVER eq "OVER")
    
40. {
    
41. print STDOUT "Child Over\n";
    
42. last;
    
43. }
    
44. elsif($RECIEVER eq "$WRITER")
    
45. {
    
46. $WRITER++;
    
47. print STDOUT "Child WRITER $WRITER\n";
    
48. print ChildWRITER "$WRITER";
    
49. }
    
50. }
    
51. }
    
52. 
    

复制代码

代码2：
pipe(ParentREADER, ChildWRITER);
pipe(ChildREADER, ParentWRITER);
$retval = fork();
if ($retval != 0) {
close (ChildREADER);
close (ChildWRITER);
select ParentWRITER;
$| = 1;
while (1)
{
print STDOUT "Parent Prepare to RECIEVER\n";
sleep 1;
$RECIEVER = <ParentREADER>;
print STDOUT "Parent RECIEVER $RECIEVER\n";
if ($RECIEVER eq "4\n")
{
print STDOUT "Parent Over\n";
print ParentWRITER "OVER\n";
last;
}
else
{
print ParentWRITER "$RECIEVER\n";
}
}
}
else {
close (ParentWRITER);
close (ParentWRITER);
select ChildWRITER;
$| = 1;
$WRITER = 1;
print STDOUT "Child WRITER $WRITER\n";
print ChildWRITER "$WRITER\n";
while (1)
{
print STDOUT "Child Prepare to RECIEVER\n";
$RECIEVER = <ChildREADER>;
if ($RECIEVER eq "OVER\n")
{
print STDOUT "Child Over\n";
last;
}
elsif($RECIEVER eq "$WRITER\n")
{
$WRITER++;
print STDOUT "Child WRITER $WRITER\n";
print ChildWRITER "$WRITER\n";
}
}
}