test.cc

#include <stdio.h>     // for fprintf()
#include <fcntl.h>
#include <unistd.h>    // for close(), read()
#include <sys/epoll.h> // for epoll_create1(), epoll_ctl(), struct epoll_event
#include <string.h>    // for strncmp
#include <errno.h>

const int kMaxEvents = 5;
const int kReadSize = 5;

int ParentMain(int pipe_in) {
  struct epoll_event event, events[kMaxEvents];
  int epoll_fd = epoll_create1(0);

  if(epoll_fd == -1) {
    perror("epoll_create1() failed");
    return 1;
  }

  event.events = EPOLLIN | EPOLLET;
  event.data.fd = pipe_in;

  if(epoll_ctl(epoll_fd, EPOLL_CTL_ADD, pipe_in, &event)) {
    perror("epoll_ctl failed");
    close(epoll_fd);
    return 1;
  }

  while (true) {
    printf("\nPolling for input...\n");
    int event_count = epoll_wait(epoll_fd, events, kMaxEvents, -1);
    printf("%d ready events\n", event_count);
    for(int i = 0; i < event_count; i++) {
      printf("Reading file descriptor '%d' -- ", events[i].data.fd);
#if defined(DRAIN_UNTIL_EAGAIN)
      const bool kShouldDrain = true;
#else
      const bool kShouldDrain = false;
#endif
      do {
        char read_buffer[1000];
        ssize_t bytes_read = read(events[i].data.fd, read_buffer, kReadSize);
        if (bytes_read < 0) {
          if (errno == EAGAIN) {
            break;
          }
          perror("read() failed");
          goto done;
        }
        printf("%zd bytes read.\n", bytes_read);
        read_buffer[bytes_read] = '\0';
        printf("Read %s\n", read_buffer);
      } while(kShouldDrain);
    }
  }
  done:

  if(close(epoll_fd))
  {
    perror("close(epoll_fd) failed\n");
    return 1;
  }
  return 0;
}

int ChildMain(int pipe_out) {
  int i = 0;
  while (true) {
    char buffer[1000];
    int bytes = snprintf(buffer, sizeof(buffer), "line %d\n", i++);
    write(pipe_out, buffer, bytes);
  }
  return 0;
}

int main()
{
  int fds[2];

  if (pipe2(fds, O_NONBLOCK) < 0) {
    perror("pipe() failed");
    return 1;
  }

  const pid_t p = fork();
  if (p < 0) {
    perror("fork() failed");
    return 1;
  } else if (p > 0) {
    return ParentMain(fds[0]);
  } else {
    return ChildMain(fds[1]);
  }
}