source: trunk/minix/test/select/test11.c@ 22

/*
 * Test name: test11.c
 *
 * Objetive: The purpose of this test is to make sure that select works
 * with pipes.
 *
 * Description:  The select checks are divided in checks on writing for the
 * parent process, which has the writing end of the pipe, and checks on reading
 * and exception on the child process, which has the reading end of pipe. So
 * when the first process is ready to write to the pipe it will request a string
 * from the terminal and send it through the pipe. If the string is 'exit' then
 * the pipe is closed. The child process is blocked in a select checking for read
 * and exception. If there is data to be read then it will perform the read and
 * prints the read data. If the pipe is closed (user typed 'exit'), the child 
 * process finishes. 
 * 
 * Jose M. Gomez
 */

#include <time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/asynchio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/select.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>
#include <signal.h>

void pipehandler(int sig)
{

}

void do_child(int data_pipe[]) 
{
        /* reads from pipe and prints out the data */
        char data[2048];
        int retval;      
        fd_set fds_read;
        fd_set fds_exception;   
        struct timeval timeout;

        signal(SIGPIPE, pipehandler);
        signal(SIGUSR1, pipehandler);

        /* first, close the write part of the pipe, since it is not needed */
        close(data_pipe[1]);
        
        while(1) {
                FD_ZERO(&fds_read);
                FD_ZERO(&fds_exception);
                FD_SET(data_pipe[0], &fds_read);
                FD_SET(data_pipe[0], &fds_exception);
                timeout.tv_sec = 5;
                timeout.tv_usec = 0;
                retval = select(data_pipe[0]+1,  &fds_read, NULL, &fds_exception, &timeout);
                if (retval == -1) {
                        perror("select");
                        fprintf(stderr, "child: Error in select\n");
                        continue;
                } else printf("child select: %d\n", retval);
                if (FD_ISSET(data_pipe[0], &fds_exception)) {
                        printf("child: exception fd set. quitting.\n");
                        break;
                }
                if (FD_ISSET(data_pipe[0], &fds_read)) {
                        printf("child: read fd set. reading.\n");
                        if ((retval = read(data_pipe[0], data, sizeof(data))) < 0) {
                                perror("read");
                                fprintf(stderr, "child: couldn't read from pipe\n");
                                exit(-1);
                        }
                        if(retval == 0) {
                                fprintf(stderr, "child: eof on pipe\n");
                                break;
                        }
                        data[retval] = '\0';
                        printf("pid %d Pipe reads (%d): %s\n", getpid(), retval, data);
                } else printf("child: no fd set\n");
        }
        
        /* probably pipe was broken, or got EOF via the pipe. */
        exit(0);
}

void do_parent(int data_pipe[]) 
{
        char data[1024];
        int retval;
        fd_set fds_write;

        signal(SIGPIPE, pipehandler);
        signal(SIGUSR1, pipehandler);

        /* first, close the read part of pipe, since it is not needed */
        close(data_pipe[0]);

        /* now enter a loop of read user input, and writing it to the pipe */
        while (1) {
                FD_ZERO(&fds_write);
                FD_SET(data_pipe[1], &fds_write);
                printf("pid %d Waiting for pipe ready to write...\n", getpid());
                retval = select(data_pipe[1]+1, NULL, &fds_write, NULL, NULL);
                if (retval == -1) {
                        perror("select");
                        fprintf(stderr, "Parent: Error in select\n");
                        exit(-1);
                }               

                printf("Input data: ");
                if(!gets(data)) {
                        printf("parent: eof; exiting\n");
                        break;
                }
                if (!strcmp(data, "exit"))
                        break;
                if (!FD_ISSET(data_pipe[1], &fds_write)) {
                        fprintf(stderr, "parent: write fd not set?! retrying\n");
                        continue;
                }
                retval = write(data_pipe[1], &data, 1024);
                if (retval == -1) {
                        perror("write");
                        fprintf(stderr, "Error writing on pipe\n");
                        exit(-1);
                }
        }

        /* got exit from user */
        close(data_pipe[1]);    /* close pipe, let child know we're done */
        wait(&retval);
        printf("Child exited with status: %d\n", retval);
        exit(0);
}

void main(void) {
        int pipes[2];
        int retval;
        int pid;        

        /* create the pipe */
        retval = pipe(pipes);
        if (retval == -1) {
                perror("pipe");
                fprintf(stderr, "Error creating the pipe\n");
                exit(-1);
        }
        pid = fork();
        if (pid == -1) {
                fprintf(stderr, "Error forking\n");
                exit(-1);
        }

        if (pid == 0) /* child proc */
                do_child(pipes);
        else
                do_parent(pipes);
}