fifo_token_ring.c

// Compile: gcc -o fifo_token_ring fifo_token_ring.c
// Run: ./fifo_token_ring N rounds
// Example: ./fifo_token_ring 4 3

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#if defined(__has_include)
#  if __has_include(<sys/wait.h>)
#    include <sys/wait.h>
#  endif
#elif defined(__unix__) || defined(__APPLE__)
#  include <sys/wait.h>
#endif
#include <string.h>

#define MAXFN 64

int main(int argc,char **argv){
    if(argc!=3){ fprintf(stderr,"Usage: %s N rounds\n",argv[0]); return 1;}
    int N = atoi(argv[1]), rounds = atoi(argv[2]);
    char names[N][MAXFN];
    for(int i=0;i<N;i++) snprintf(names[i],MAXFN,"/tmp/fifo_ring_%d",i);

    // create FIFOs
    for(int i=0;i<N;i++){
        mkfifo(names[i], 0666);
    }

    for(int i=0;i<N;i++){
        pid_t pid = fork();
        if(pid<0){ perror("fork"); exit(1); }
        if(pid==0){
            int read_fd = open(names[i], O_RDONLY);
            int write_fd = open(names[(i+1)%N], O_WRONLY);
            if(read_fd<0||write_fd<0){ perror("open fifo"); exit(1); }
            while(1){
                int token;
                ssize_t r = read(read_fd, &token, sizeof(int));
                if(r<=0) break;
                printf("Proc %d pid %d got token=%d\n", i, getpid(), token);
                fflush(stdout);
                token++;
                if(write(write_fd, &token, sizeof(int))<=0) break;
            }
            close(read_fd); close(write_fd);
            _exit(0);
        }
    }

    // parent: open one FIFO for writing to start the token (to FIFO 0)
    int start_fd = open(names[0], O_WRONLY);
    if(start_fd<0){ perror("open start"); }
    int token = 0, maxToken = N*rounds;
    if(write(start_fd, &token, sizeof(int))<=0) perror("start write");
    close(start_fd);

    sleep(1 + rounds * N / 10 + 1);
    for(int i=0;i<N;i++) unlink(names[i]);
    for(int i=0;i<N;i++) wait(NULL);
    return 0;
}