有关消息队列问题的请教

发布于 2011-10-24 15:15:39 浏览：4200 订阅该版

7 个回答

bernard 2011-10-24

这家伙很懒，什么也没写！

airanver 2011-10-25

这家伙很懒，什么也没写！

SimonLeung 2013-05-31

这家伙很懒，什么也没写！

SimonLeung 2013-05-31

这家伙很懒，什么也没写！

bernard 2013-05-31

这家伙很懒，什么也没写！

SimonLeung 2013-05-31

这家伙很懒，什么也没写！

>OSQAccept是干什么的？对uc不熟悉，一般其他的一些RTOS并没有这样的功能

---

```

/*
*********************************************************************************************************
*                                      ACCEPT MESSAGE FROM QUEUE
*
* Description: This function checks the queue to see if a message is available.  Unlike OSQPend(),
*              OSQAccept() does not suspend the calling task if a message is not available.
*
* Arguments  : pevent        is a pointer to the event control block
*
*              err           is a pointer to where an error message will be deposited.  Possible error
*                            messages are:
*
*                            OS_NO_ERR           The call was successful and your task received a
*                                                message.
*                            OS_ERR_EVENT_TYPE   You didn't pass a pointer to a queue
*                            OS_ERR_PEVENT_NULL  If 'pevent' is a NULL pointer
*                            OS_Q_EMPTY          The queue did not contain any messages
*
* Returns    : != (void *)0  is the message in the queue if one is available.  The message is removed
*                            from the so the next time OSQAccept() is called, the queue will contain
*                            one less entry.
*              == (void *)0  if you received a NULL pointer message
*                            if the queue is empty or,
*                            if 'pevent' is a NULL pointer or,
*                            if you passed an invalid event type
*
* Note(s)    : As of V2.60, you can now pass NULL pointers through queues.  Because of this, the argument
*              'err' has been added to the API to tell you about the outcome of the call.
*********************************************************************************************************
*/

#if OS_Q_ACCEPT_EN > 0
void  *OSQAccept (OS_EVENT *pevent, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */
    OS_CPU_SR  cpu_sr;
#endif
    void      *msg;
    OS_Q      *pq;

#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {               /* Validate 'pevent'                                  */
        *err = OS_ERR_PEVENT_NULL;
        return ((void *)0);
    }
#endif
    if (pevent->OSEventType != OS_EVENT_TYPE_Q) {/* Validate event block type                          */
        *err = OS_ERR_EVENT_TYPE;
        return ((void *)0);
    }
    OS_ENTER_CRITICAL();
    pq = (OS_Q *)pevent->OSEventPtr;             /* Point at queue control block                       */
    if (pq->OSQEntries > 0) {                    /* See if any messages in the queue                   */
        msg = *pq->OSQOut++;                     /* Yes, extract oldest message from the queue         */
        pq->OSQEntries--;                        /* Update the number of entries in the queue          */
        if (pq->OSQOut == pq->OSQEnd) {          /* Wrap OUT pointer if we are at the end of the queue */
            pq->OSQOut = pq->OSQStart;
        }
        *err = OS_NO_ERR;
    } else {
        *err = OS_Q_EMPTY;
        msg  = (void *)0;                        /* Queue is empty                                     */
    }
    OS_EXIT_CRITICAL();
    return (msg);                                /* Return message received (or NULL)                  */
}
#endif
```

研究了一会儿，发现可以通过检查

```
rt_uint16_t entry;                                  /**< index of messages in the queue         */
```

来实现