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管道的写阻塞问题！

时间：2010-08-18

来源：互联网

请问对一个管道写时，如果管道缓冲区不够，是不是会阻塞？
如果是的话，那么下面这个程序运行的时候，为什么一开始立马就打印了5000？而不是等读进程读取后再写？
如果不是，那么关于管道写数据时的阻塞问题，正解是什么？

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
//PIPE_BUF = 4096
int main()
{
int fd[2];
int ret,request;
char rbuf[4096];
char wbuf[4096*2];
char *msg="hello,pipe!",*msg2="hello,I come here ,too!";
pid_t pid;
int stat_val;
if(pipe(fd)<0)
{
printf("pipe error\n");
exit(1);
}
if((pid=fork())==0)
{
//child process write
close(fd[0]);
ret=write(fd[1],wbuf,1024);
printf("I am writer and I write %d Byte data\n",ret);
ret=write(fd[1],wbuf,5000);
printf("I am writer and I write %d Byte data\n",ret);
printf("writer has over\n");
close(fd[1]);
exit(0);
}
else if(pid>0)
{
//parent process read
close(fd[1]);
sleep(5);
while(1)
{
sleep(1);
ret=read(fd[0],rbuf,1000);
printf("I am reader and the num of reading data is %d\n",ret);
}
close(fd[0]);
exit(0);
}
}

复制代码

作者: edsionte 发布时间: 2010-08-18

QUOTE:

请问对一个管道写时，如果管道缓冲区不够，是不是会阻塞？
如果是的话，那么下面这个程序运行的时候，为什 ...
edsionte 发表于 2010-08-18 23:11

有问题？

QUOTE:

I am writer and I write 1024 Byte data
I am writer and I write 5000 Byte data
writer has over
I am reader and the num of reading data is 1000
I am reader and the num of reading data is 1000
I am reader and the num of reading data is 1000
I am reader and the num of reading data is 1000
I am reader and the num of reading data is 1000
I am reader and the num of reading data is 1000
I am reader and the num of reading data is 24
I am reader and the num of reading data is 0
I am reader and the num of reading data is 0
I am reader and the num of reading data is 0

作者: 叶叶叶Yeah 发布时间: 2010-08-19

回复 edsionte

是的，上一个帖子我已经说过了。你知道你这里的pipe大小是多少？（大小是 PIPE_SIZE，在内核中定义）man7 pipe好好看看再说

作者: churchmice 发布时间: 2010-08-19