mq_getattr.c

来自「Newlib 嵌入式 C库 标准实现代码」· C语言 代码 · 共 53 行

/* Copyright 2002, Red Hat Inc. */

#include <mqueue.h>
#include <errno.h>
#include <sys/sem.h>
#include <string.h>
#define _LIBC 1
#include <sys/lock.h>
#undef _LIBC

#include "mqlocal.h"

int
mq_getattr (mqd_t msgid, struct mq_attr *mqstat)
{
  struct libc_mq *info;
  struct sembuf sb0 = {0, -1, 0};
  int num_msgs;
  int rc = 0;

  info = __find_mq (msgid);

  if (info == NULL)
    {
      errno = EBADF;
      return -1;
    }

  /* temporarily lock message queue */
  semop (info->semid, &sb0, 1);

  num_msgs = semctl (info->semid, 3, GETVAL);
  if (num_msgs >= 0)
    {
      memcpy (mqstat, info->attr, sizeof(struct mq_attr));
      mqstat->mq_curmsgs = num_msgs;
    }
  else
    rc = -1;

  /* release message queue */
  sb0.sem_op = 1;
  semop (info->semid, &sb0, 1);

  return rc;
}