The pipeline of Linux system Programming (II) Pipe reading and writing rules and PIPE Capacity, pipe_buf

First, when there is no data to read

O_nonblock Disable:read Call blocking, the process suspends execution until the data arrives.

The O_nonblock enable:read call returns a -1,errno value of Eagain.

The sample program is as follows:

/************************************************************************* 
 > File name:process_.c 
 > Author:simba 
 > Mail:dameng34@163.com 
 > Created time:sat Feb 2013 02:34:02 PM CST 
 * * * /
 #include <sys/types.h> 
 # Include<sys/stat.h> 
 #include <unistd.h> 
 #include <fcntl.h> 
 #include <stdio.h> 
 #include <stdlib.h> 
 #include <errno.h> 
 #include <string.h> 
 #include <signal.h 
 #define ERR_EXIT (m) \ 
 Do {\ 
 Perror (m), \ 
 EXIT (exit_failure); \ 
} while (0) 
    int main (int argc, char *argv[]) 
 {
 int pipefd[2]; 
    if (pipe (PIPEFD) = = 1) 
 Err_exit ("pipe error"); 
 pid_t pid; 
 pid = fork ();    
 if (pid = = 1) 
 Err_exit ("fork Error"); 
        if (PID = = 0) 
 {
 Sleep (3); 
 Close (pipefd[0]); 
 WritE (pipefd[1], "Hello", 5); 
 Close (pipefd[1]); 
 Exit (exit_success);    
} 
 Close (pipefd[1]); 
 Char buf[10] = {0}; 
 INT flags = FCNTL (pipefd[0], F_GETFL); 
 Fcntl (pipefd[0], F_SETFL, Flags | O_nonblock); The o_nonblock 
 int ret = read (Pipefd[0], buf, 10) of the Enable FD;///default is disable FD O_nonblock 
 if (ret = 1)//parent process not    will block, error returns 
 Err_exit ("read error"); 
 printf ("buf=%s\n", buf); 
 return 0; 
} 

Deliberately sleep in the subprocess 3s, so that the parent process is scheduled to run, and the read-end file descriptor flag set to Non-blocking, that is, immediately error return, as follows.

simba@ubuntu:~/documents/code/linux_programming/apue/pipe$./pipe_block

Read Error:resource temporarily unavailable