trywait.c

来自「这个是学习嵌入式开发的重要例子」· C语言 代码 · 共 55 行

#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <string.h>
#include <errno.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(int argc, char **argv)
{
  if (argc < 2)
  {
    fprintf(stdout, "Usage: %s <name>\n", argv[0]);
    exit(1);
  }

  sem_t *sem = NULL;

  if ((sem = sem_open(argv[1], O_RDONLY)) == SEM_FAILED)
  {
    fprintf(stderr, "sem_open() failed: %s\n", strerror(errno));
    exit(1);
  }

  int value;

  //int sem_getvalue(sem_t *restrict sem, int *restrict sval);
  sem_getvalue(sem, &value);
  fprintf(stdout, "value = %d\n", value);

  //int sem_trywait(sem_t * sem);
  //int sem_wait(sem_t * sem);
  if (sem_trywait(sem) < 0)
  {
    fprintf(stderr, "sem_wait() failed: %s\n", strerror(errno));

    if (errno == EAGAIN)
    {
      fprintf(stdout, "sem_trywait() returned EAGAIN.\n");
    }
    else
    {
      sem_close(sem);
      exit(1);
    }
  }

  sem_getvalue(sem, &value);
  fprintf(stdout, "value = %d\n", value);

  sem_close(sem);

  return 0;
}