test of O_NONBLOCK from APUE Chapter 12

nonblock_apue12.c

#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>

void set_fl(int fd, int flags);
void clr_fl(int fd, int flags);

char buf[100000];

int main(void) {
  int ntowrite, nwrite;
  char *ptr;

  ntowrite = read(STDIN_FILENO, buf, sizeof(buf));
  fprintf(stderr, "read %d byts\n", ntowrite);

  set_fl(STDOUT_FILENO, O_NONBLOCK);

  for (ptr = buf; ntowrite > 0; ) {
    errno = 0;
    nwrite = write(STDOUT_FILENO, ptr, ntowrite);
    fprintf(stderr, "nwrite = %d, errno = %d, err_message = '%s'\n", nwrite, errno, strerror(errno));
    if (nwrite > 0) {
      ptr += nwrite;
      ntowrite -= nwrite;
    }
  }

  clr_fl(STDOUT_FILENO, O_NONBLOCK);
  return 0;
}

void set_fl(int fd, int flags) {
  int val;

  if ((val = fcntl(fd, F_GETFL, 0)) < 0) {
    fprintf(stderr, "fcntl F_GETFL error");
    exit(1);
  }

  val |= flags;  /* turn on flags */

  if (fcntl(fd, F_SETFL, val) < 0) {
    fprintf(stderr, "fcntl F_SETFL error");
    exit(1);
  }
}

void clr_fl(int fd, int flags) {
  int val;

  if ((val = fcntl(fd, F_GETFL, 0)) < 0) {
    fprintf(stderr, "fcntl F_GETFL error");
    exit(1);
  }

  val &= ~flags;  /* turn flags off */

  if (fcntl(fd, F_SETFL, val) < 0) {
    fprintf(stderr, "fcntl F_SETFL error");
    exit(1);
  }
}