CS471/571 - Operating Systems

Displaying ./code/Semaphores/writer.c

#include <stdio.h>
#include <sys/stat.h>
#include <semaphore.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>

#define PIPESIZE	10

// Compile: gcc -o writer writer.c -lrt -lpthread

struct pipe {
  sem_t lock, block;
  char data[PIPESIZE];
  int wp, rp, initialized;
};

int main(void)
{
  char *data = "abcdefghijklmnopqrstuvwxyz";
  struct pipe pdata;
  int fd = shm_open("/my_pipe", O_RDWR | O_CREAT | O_TRUNC, 0666);
  if (fd < 0) {
    perror("shm_open");
    return 1;
  }

  memset(&pdata, 0, sizeof(struct pipe));
  write(fd, &pdata, sizeof(struct pipe));

  struct pipe *pipe = mmap(NULL, sizeof(struct pipe),
       PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  if (pipe == MAP_FAILED) {
    perror("mmap");
    return 1;
  }
  sem_init(&(pipe->lock), 1, 0);
  sem_init(&(pipe->block), 1, 0);
  pipe->initialized = 1;

  int c = 0;
  while(1) {
    while ((pipe->wp+1) % PIPESIZE == pipe->rp) {
      sem_post(&(pipe->lock));
      fprintf(stderr," blocking...\n");
      sem_wait(&(pipe->block));
    }
    pipe->data[pipe->wp] = c+'a';
    fprintf(stderr,"%c", c+'a');
    c=(c+1)%26;
    pipe->wp = (pipe->wp+1) % PIPESIZE;
  }
}