管道中断，FIFO文件

Question

I'm trying a program to use FIFO file, but I'm getting Broken pipe as output. Here is the code -

#include<iostream>
#include<stdlib.h>
#include<fcntl.h>
#include<stdio.h>
#include<string.h>
#include<unistd.h>
#include<sys/stat.h>
#include<sys/types.h>
using namespace std;
int main(int argc,char *argv[])
{
int fd; //stores file descriptor returnd from open
char buf[256];
if(argc<2||argc>3)
{
    cout<<"Invalid Arguments";
    return 1;
}

mkfifo(argv[1],0777);
if(argc==3)
{   
    cout<<"Writer\n";
    if((fd=open(argv[1],O_WRONLY))==-1)
    {
        perror("open");
        return 1;
    }
    write(fd,argv[2],strlen(argv[2]));
    sleep(10);
}
else
{   cout<<"Reader\n";
    if((fd=open(argv[1],O_RDONLY|O_NONBLOCK))==-1)
    {       
        perror("open");
        return 1;
    }

    read(fd,&buf,sizeof(buf));
    cout<<buf;

}
 close(fd);
 return 1;
 }

Output: Below Fifo is the name of the file and Hello is the content.

 ./a.out fifo hello & Writer ./a.out fifo Reader [1]+ Broken pipe 

I should get "Hello" as the output. Can anyone help?

Answer 1

Your write happens before you start your reader. When you write to a pipe and it has no reader you get SIGPIPE.

In this particular design, you need to handle SIGPIPE with retry logic.

Answer 2

The error you get is EPIPE and if you read a write manual you will see that you get EPIPE when

fd is connected to a pipe or socket whose reading end is closed.

You get this error because you open the reading end of the pipe in non-blocking mode, which means the read call will not block and wait for data to be received, instead when the read call immediately return you close the pipe and exit the process.

That means when you run the writer there is no one waiting for the data you write and you get the error.

You need to run the read and the writer in opposite order: First the writer so it writes to the pipe, and then the reader to read the data from the pipe.