root/select.c

DEFINITIONS

1. main

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/fcntl.h>

#define MAX(a,b)  (((a)<(b))?(b):(a))

int main() {
        int pipes[3][2];
        fd_set readset,writeset;
        int i,max,res;
        struct timeval to;
        char line[100];

        for (i=0;i<3;i++)
                pipe(pipes[i]);


        if (fork()) 
                if (fork()) 
                        if (fork()) { //parent code here
                                close(pipes[0][1]);
                                close(pipes[1][1]);
                                close(pipes[2][0]);
                                /*
                                fcntl(pipes[0][0],F_SETFL,O_NONBLOCK);
                                fcntl(pipes[1][0],F_SETFL,O_NONBLOCK);
                                fcntl(pipes[2][1],F_SETFL,O_NONBLOCK);
                                */
                                /* 0 and 1 for reading, 2 for writing */
                                FD_ZERO(&readset);
                                FD_ZERO(&writeset);
                                FD_SET(pipes[0][0],&readset);
                                FD_SET(pipes[1][0],&readset);
                                FD_SET(pipes[2][1],&writeset);
                                to.tv_sec=5;
                                to.tv_usec=0;
max=MAX(pipes[0][0],MAX(pipes[1][0],pipes[2][1]))+1;
while (1) {
        res=select(max,&readset,&writeset,NULL,&to);
        if (res<0)
                return 0;
        else if (res==0)  {
                printf("Timeout\n");
        } else {
                if (FD_ISSET(pipes[0][0],&readset)) {
                        read(pipes[0][0],line,100);
                        printf("Read[0]:%s\n",line);
                } 
                if (FD_ISSET(pipes[1][0],&readset)) {
                        read(pipes[1][0],line,100);
                        printf("Read[1]:%s\n",line);
                }
                if (FD_ISSET(pipes[2][1],&writeset)) {
                        write(pipes[2][1],"parent outputs\n",15);
                }
        }
        FD_ZERO(&readset);
        FD_ZERO(&writeset);
        FD_SET(pipes[0][0],&readset);
        FD_SET(pipes[1][0],&readset);
        FD_SET(pipes[2][1],&writeset);
        to.tv_sec=5;
        to.tv_usec=0;
}

                        } else {
                                srand(getpid());
                                close(pipes[0][0]);
                                dup2(pipes[0][1],1);
                                i=0;
                                while (1) {
                                        i++;
                                        sleep(rand()%20);
                                        printf("%d: %d\n",getpid(),i);
                                        fflush(stdout);
                                }
                        }
                else {
                        srand(getpid());
                        close(pipes[1][0]);
                        dup2(pipes[1][1],1);
                        i=0;
                        while (1) {
                                i++;
                                sleep(rand()%20);
                                printf("%d: %d\n",getpid(),i);
                                fflush(stdout);
                        }
                }
        else {
                srand(getpid());
                close(pipes[2][1]);
                dup2(pipes[2][0],0);
                i=0;
                while (1) {
                        i++;
                        sleep(rand()%20);
                        fflush(stdin);
                        fgets(line,100,stdin);
                        printf("%d: %s\n",getpid(),line);
                }
        }

        return 0;
}