RT-Thread IPC Message Queue

• 特性：可接受不固定長度的訊息

結構

File: rtdef.h

#ifdef RT_USING_MESSAGEQUEUE
/**
 * message queue structure
 */
struct rt_messagequeue
{
    struct rt_ipc_object parent;                        /**< inherit from ipc_object */

    void                *msg_pool;                      /**< start address of message queue */

    rt_uint16_t          msg_size;                      /**< message size of each message */
    rt_uint16_t          max_msgs;                      /**< max number of messages */

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

    void                *msg_queue_head;                /**< list head */
    void                *msg_queue_tail;                /**< list tail */
    void                *msg_queue_free;                /**< pointer indicated the free node of queue */
};
typedef struct rt_messagequeue *rt_mq_t;
#endif

---

建立 message queue

動態記憶體管理

rt_mq_create

功能	回傳值
建立 message queue	message queue

*name	msg_size	max_msgs	flag
名字	一封訊息的大小	訊息數上限	FIFO / PRIO

/**
 * This function will create a message queue object from system resource
 *
 * @param name the name of message queue
 * @param msg_size the size of message
 * @param max_msgs the maximum number of message in queue
 * @param flag the flag of message queue
 *
 * @return the created message queue, RT_NULL on error happen
 */
rt_mq_t rt_mq_create(const char *name,
                     rt_size_t   msg_size,
                     rt_size_t   max_msgs,
                     rt_uint8_t  flag)
{
    struct rt_messagequeue *mq;
    struct rt_mq_message *head;
    register rt_base_t temp;

    RT_DEBUG_NOT_IN_INTERRUPT;

    /* allocate object */
    mq = (rt_mq_t)rt_object_allocate(RT_Object_Class_MessageQueue, name);
    if (mq == RT_NULL)
        return mq;

    /* set parent */
    mq->parent.parent.flag = flag;

    /* init ipc object */
    rt_ipc_object_init(&(mq->parent));

• 首先要一塊物件給 message queue，並同時填入 flag 及初始化

    /* init message queue */

    /* get correct message size */
    mq->msg_size = RT_ALIGN(msg_size, RT_ALIGN_SIZE);
    mq->max_msgs = max_msgs;

• 設定訊息的大小，與訊息數量的上限

RT_ALGIN 目的在對齊訊息的大小，根據不同板子所定義不同的 RT_ALIGN_SIZE 會有所差別
#define RT_ALIGN(size, align) (((size) + (align) - 1) & ~((align) - 1))

• 如傳進來的是 RT_ALGIN(7,8) 則結果是 8
• 如傳進來的是 RT_ALGIN(13,4) 則結果是 16
• 即結果為大於後值的最小倍數

    /* allocate message pool */
    mq->msg_pool = RT_KERNEL_MALLOC((mq->msg_size + sizeof(struct rt_mq_message)) * mq->max_msgs);
    if (mq->msg_pool == RT_NULL)
    {
        rt_mq_delete(mq);

        return RT_NULL;
    }

• 接著需 allocate 適當的記憶體存放訊息

    /* init message list */
    mq->msg_queue_head = RT_NULL;
    mq->msg_queue_tail = RT_NULL;

    /* init message empty list */
    mq->msg_queue_free = RT_NULL;
    for (temp = 0; temp < mq->max_msgs; temp ++)
    {
        head = (struct rt_mq_message *)((rt_uint8_t *)mq->msg_pool +
                                        temp * (mq->msg_size + sizeof(struct rt_mq_message)));
        head->next = mq->msg_queue_free;
        mq->msg_queue_free = head;
    }

• 先將頭尾設為空，再一塊一塊的將 msg_pool 插在 free list 的第一顆

    /* the initial entry is zero */
    mq->entry = 0;

    return mq;
}
RTM_EXPORT(rt_mq_create);

• 最後設定 entry 為 0

---

靜態記憶體管理

rt_mq_init

功能	回傳值
初始化 message queue	RT_EOK

mq	*name	*msgpool	msg_size	pool_size	flag
message queue 本體	名字	存放訊息的位址	一封訊息的大小	存放訊息的大小	FIFO / PRIO

/**
 * This function will initialize a message queue and put it under control of
 * resource management.
 *
 * @param mq the message object
 * @param name the name of message queue
 * @param msgpool the beginning address of buffer to save messages
 * @param msg_size the maximum size of message
 * @param pool_size the size of buffer to save messages
 * @param flag the flag of message queue
 *
 * @return the operation status, RT_EOK on successful
 */
rt_err_t rt_mq_init(rt_mq_t     mq,
                    const char *name,
                    void       *msgpool,
                    rt_size_t   msg_size,
                    rt_size_t   pool_size,
                    rt_uint8_t  flag)
{
    struct rt_mq_message *head;
    register rt_base_t temp;

    /* parameter check */
    RT_ASSERT(mq != RT_NULL);

    /* init object */
    rt_object_init(&(mq->parent.parent), RT_Object_Class_MessageQueue, name);

    /* set parent flag */
    mq->parent.parent.flag = flag;

    /* init ipc object */
    rt_ipc_object_init(&(mq->parent));

• 這裡就不需要去要一塊物件，直接拿來用即可

    /* set messasge pool */
    mq->msg_pool = msgpool;

    /* get correct message size */
    mq->msg_size = RT_ALIGN(msg_size, RT_ALIGN_SIZE);
    mq->max_msgs = pool_size / (mq->msg_size + sizeof(struct rt_mq_message));

    /* init message list */
    mq->msg_queue_head = RT_NULL;
    mq->msg_queue_tail = RT_NULL;

    /* init message empty list */
    mq->msg_queue_free = RT_NULL;
    for (temp = 0; temp < mq->max_msgs; temp ++)
    {
        head = (struct rt_mq_message *)((rt_uint8_t *)mq->msg_pool +
                                        temp * (mq->msg_size + sizeof(struct rt_mq_message)));
        head->next = mq->msg_queue_free;
        mq->msg_queue_free = head;
    }

    /* the initial entry is zero */
    mq->entry = 0;

    return RT_EOK;
}
RTM_EXPORT(rt_mq_init);

• 其餘的動作皆與上面相同

---

刪除 message queue

動態記憶體管理

rt_mq_delete

功能	回傳值
刪除 message queue	RT_EOK

mq
欲刪除的 message queue

/**
 * This function will delete a message queue object and release the memory
 *
 * @param mq the message queue object
 *
 * @return the error code
 */
rt_err_t rt_mq_delete(rt_mq_t mq)
{
    RT_DEBUG_NOT_IN_INTERRUPT;

    /* parameter check */
    RT_ASSERT(mq != RT_NULL);
    RT_ASSERT(rt_object_get_type(&mq->parent.parent) == RT_Object_Class_MessageQueue);
    RT_ASSERT(rt_object_is_systemobject(&mq->parent.parent) == RT_FALSE);

    /* resume all suspended thread */
    rt_ipc_list_resume_all(&(mq->parent.suspend_thread));

• 先把正在等待收訊息的 thread 叫醒

    /* free message queue pool */
    RT_KERNEL_FREE(mq->msg_pool);

    /* delete message queue object */
    rt_object_delete(&(mq->parent.parent));

    return RT_EOK;
}
RTM_EXPORT(rt_mq_delete);

• 接著 free msg_pool，並刪除物件

---

靜態記憶體管理

rt_mq_detach

功能	回傳值
刪除 message queue	RT_EOK

mq
欲刪除的 message queue

/**
 * This function will detach a message queue object from resource management
 *
 * @param mq the message queue object
 *
 * @return the operation status, RT_EOK on successful
 */
rt_err_t rt_mq_detach(rt_mq_t mq)
{
    /* parameter check */
    RT_ASSERT(mq != RT_NULL);
    RT_ASSERT(rt_object_get_type(&mq->parent.parent) == RT_Object_Class_MessageQueue);
    RT_ASSERT(rt_object_is_systemobject(&mq->parent.parent));

    /* resume all suspended thread */
    rt_ipc_list_resume_all(&mq->parent.suspend_thread);

    /* detach message queue object */
    rt_object_detach(&(mq->parent.parent));

    return RT_EOK;
}
RTM_EXPORT(rt_mq_detach);

• 這裡的 msg_pool 就不需要 free

---

傳送訊息

rt_mq_send

功能	回傳值
傳送訊息	RT_EOK

mq	*buffer	size
欲傳送的 message queue	訊息資料	訊息大小

/**
 * This function will send a message to message queue object, if there are
 * threads suspended on message queue object, it will be waked up.
 *
 * @param mq the message queue object
 * @param buffer the message
 * @param size the size of buffer
 *
 * @return the error code
 */
rt_err_t rt_mq_send(rt_mq_t mq, void *buffer, rt_size_t size)
{
    register rt_ubase_t temp;
    struct rt_mq_message *msg;

    /* parameter check */
    RT_ASSERT(mq != RT_NULL);
    RT_ASSERT(rt_object_get_type(&mq->parent.parent) == RT_Object_Class_MessageQueue);
    RT_ASSERT(buffer != RT_NULL);
    RT_ASSERT(size != 0);

    /* greater than one message size */
    if (size > mq->msg_size)
        return -RT_ERROR;

    RT_OBJECT_HOOK_CALL(rt_object_put_hook, (&(mq->parent.parent)));

    /* disable interrupt */
    temp = rt_hw_interrupt_disable();

    /* get a free list, there must be an empty item */
    msg = (struct rt_mq_message *)mq->msg_queue_free;
    /* message queue is full */
    if (msg == RT_NULL)
    {
        /* enable interrupt */
        rt_hw_interrupt_enable(temp);

        return -RT_EFULL;
    }

• 首先確定 message queue 沒滿（即 free list 不為空）
• 如果滿了，回傳 FULL

    /* move free list pointer */
    mq->msg_queue_free = msg->next;

• 接著 free list 往下一顆走

    /* enable interrupt */
    rt_hw_interrupt_enable(temp);

    /* the msg is the new tailer of list, the next shall be NULL */
    msg->next = RT_NULL;
    /* copy buffer */
    rt_memcpy(msg + 1, buffer, size);

• 將訊息填入從 free list 拿的一顆（msg），這顆待會是新的尾巴（設定 next = NULL）

    /* disable interrupt */
    temp = rt_hw_interrupt_disable();
    /* link msg to message queue */
    if (mq->msg_queue_tail != RT_NULL)
    {
        /* if the tail exists, */
        ((struct rt_mq_message *)mq->msg_queue_tail)->next = msg;
    }

• 如果尾巴不為空（也就是 message queue 有東西），將原本的尾巴指向 msg

    /* set new tail */
    mq->msg_queue_tail = msg;
    /* if the head is empty, set head */
    if (mq->msg_queue_head == RT_NULL)
        mq->msg_queue_head = msg;

• 設定新的尾巴
• 如果頭為空（也就是 message queue 為空），設定新的頭

    /* increase message entry */
    mq->entry ++;

• 最後更新 entry

    /* resume suspended thread */
    if (!rt_list_isempty(&mq->parent.suspend_thread))
    {
        rt_ipc_list_resume(&(mq->parent.suspend_thread));

        /* enable interrupt */
        rt_hw_interrupt_enable(temp);

        rt_schedule();

        return RT_EOK;
    }

    /* enable interrupt */
    rt_hw_interrupt_enable(temp);

    return RT_EOK;
}
RTM_EXPORT(rt_mq_send);

• 如果有人在等待接收訊息，叫醒他

---

傳送緊急訊息

• 與上面不同的是：這裡將新訊息插入第一顆

rt_mq_urgent

功能	回傳值
傳送緊急訊息	RT_EOK

mq	*buffer	size
欲傳送的 message queue	訊息資料	訊息大小

/**
 * This function will send an urgent message to message queue object, which
 * means the message will be inserted to the head of message queue. If there
 * are threads suspended on message queue object, it will be waked up.
 *
 * @param mq the message queue object
 * @param buffer the message
 * @param size the size of buffer
 *
 * @return the error code
 */
rt_err_t rt_mq_urgent(rt_mq_t mq, void *buffer, rt_size_t size)
{
    register rt_ubase_t temp;
    struct rt_mq_message *msg;

    /* parameter check */
    RT_ASSERT(mq != RT_NULL);
    RT_ASSERT(rt_object_get_type(&mq->parent.parent) == RT_Object_Class_MessageQueue);
    RT_ASSERT(buffer != RT_NULL);
    RT_ASSERT(size != 0);

    /* greater than one message size */
    if (size > mq->msg_size)
        return -RT_ERROR;

    RT_OBJECT_HOOK_CALL(rt_object_put_hook, (&(mq->parent.parent)));

    /* disable interrupt */
    temp = rt_hw_interrupt_disable();

    /* get a free list, there must be an empty item */
    msg = (struct rt_mq_message *)mq->msg_queue_free;
    /* message queue is full */
    if (msg == RT_NULL)
    {
        /* enable interrupt */
        rt_hw_interrupt_enable(temp);

        return -RT_EFULL;
    }
    /* move free list pointer */
    mq->msg_queue_free = msg->next;

    /* enable interrupt */
    rt_hw_interrupt_enable(temp);

    /* copy buffer */
    rt_memcpy(msg + 1, buffer, size);

• 因為要插在第一顆，next 就不用設定為空了

    /* disable interrupt */
    temp = rt_hw_interrupt_disable();

    /* link msg to the beginning of message queue */
    msg->next = mq->msg_queue_head;
    mq->msg_queue_head = msg;

• 這裡就將新訊息插在第一顆

    /* if there is no tail */
    if (mq->msg_queue_tail == RT_NULL)
        mq->msg_queue_tail = msg;

• 如果原本的 message queue 為空，設定新的尾巴

    /* increase message entry */
    mq->entry ++;

    /* resume suspended thread */
    if (!rt_list_isempty(&mq->parent.suspend_thread))
    {
        rt_ipc_list_resume(&(mq->parent.suspend_thread));

        /* enable interrupt */
        rt_hw_interrupt_enable(temp);

        rt_schedule();

        return RT_EOK;
    }

    /* enable interrupt */
    rt_hw_interrupt_enable(temp);

    return RT_EOK;
}
RTM_EXPORT(rt_mq_urgent);

• 其他的動作皆相同

---

接收訊息

rt_mq_recv

功能	回傳值
接收訊息	RT_EOK

mq	*buffer	size	timeout
欲訊息 message queue	訊息存放處	訊息存放處大小	等待時間（如果需要）

/**
 * This function will receive a message from message queue object, if there is
 * no message in message queue object, the thread shall wait for a specified
 * time.
 *
 * @param mq the message queue object
 * @param buffer the received message will be saved in
 * @param size the size of buffer
 * @param timeout the waiting time
 *
 * @return the error code
 */
rt_err_t rt_mq_recv(rt_mq_t    mq,
                    void      *buffer,
                    rt_size_t  size,
                    rt_int32_t timeout)
{
    struct rt_thread *thread;
    register rt_ubase_t temp;
    struct rt_mq_message *msg;
    rt_uint32_t tick_delta;

    /* parameter check */
    RT_ASSERT(mq != RT_NULL);
    RT_ASSERT(rt_object_get_type(&mq->parent.parent) == RT_Object_Class_MessageQueue);
    RT_ASSERT(buffer != RT_NULL);
    RT_ASSERT(size != 0);

    /* initialize delta tick */
    tick_delta = 0;
    /* get current thread */
    thread = rt_thread_self();
    RT_OBJECT_HOOK_CALL(rt_object_trytake_hook, (&(mq->parent.parent)));

    /* disable interrupt */
    temp = rt_hw_interrupt_disable();

    /* for non-blocking call */
    if (mq->entry == 0 && timeout == 0)
    {
        rt_hw_interrupt_enable(temp);

        return -RT_ETIMEOUT;
    }

    /* message queue is empty */
    while (mq->entry == 0)
    {
        RT_DEBUG_IN_THREAD_CONTEXT;

        /* reset error number in thread */
        thread->error = RT_EOK;

        /* no waiting, return timeout */
        if (timeout == 0)
        {
            /* enable interrupt */
            rt_hw_interrupt_enable(temp);

            thread->error = -RT_ETIMEOUT;

            return -RT_ETIMEOUT;
        }

• 如果 message queue 為空，且不等待，回傳 TIMEOUT

        /* suspend current thread */
        rt_ipc_list_suspend(&(mq->parent.suspend_thread),
                            thread,
                            mq->parent.parent.flag);

• 如要等待，將 thread 掛在等待鏈上

        /* has waiting time, start thread timer */
        if (timeout > 0)
        {
            /* get the start tick of timer */
            tick_delta = rt_tick_get();

            RT_DEBUG_LOG(RT_DEBUG_IPC, ("set thread:%s to timer list\n",
                                        thread->name));

            /* reset the timeout of thread timer and start it */
            rt_timer_control(&(thread->thread_timer),
                             RT_TIMER_CTRL_SET_TIME,
                             &timeout);
            rt_timer_start(&(thread->thread_timer));
        }

• 並啟動一個 timer

        /* enable interrupt */
        rt_hw_interrupt_enable(temp);

        /* re-schedule */
        rt_schedule();

• 開始等待，做一次調度

        /* recv message */
        if (thread->error != RT_EOK)
        {
            /* return error */
            return thread->error;
        }

        /* disable interrupt */
        temp = rt_hw_interrupt_disable();

        /* if it's not waiting forever and then re-calculate timeout tick */
        if (timeout > 0)
        {
            tick_delta = rt_tick_get() - tick_delta;
            timeout -= tick_delta;
            if (timeout < 0)
                timeout = 0;
        }
    }

• 如跳回來，重新計算 timeout

    /* get message from queue */
    msg = (struct rt_mq_message *)mq->msg_queue_head;

    /* move message queue head */
    mq->msg_queue_head = msg->next;
    /* reach queue tail, set to NULL */
    if (mq->msg_queue_tail == msg)
        mq->msg_queue_tail = RT_NULL;

• 如果 message queue 有資料，拿第一顆，同時更新 head（tail，如果需要）

    /* decrease message entry */
    mq->entry --;

• 更新 entry

    /* enable interrupt */
    rt_hw_interrupt_enable(temp);

    /* copy message */
    rt_memcpy(buffer, msg + 1, size > mq->msg_size ? mq->msg_size : size);

• 接著複製找到的訊息

    /* disable interrupt */
    temp = rt_hw_interrupt_disable();
    /* put message to free list */
    msg->next = (struct rt_mq_message *)mq->msg_queue_free;
    mq->msg_queue_free = msg;
    /* enable interrupt */
    rt_hw_interrupt_enable(temp);

    RT_OBJECT_HOOK_CALL(rt_object_take_hook, (&(mq->parent.parent)));

    return RT_EOK;
}
RTM_EXPORT(rt_mq_recv);

• 最後將 msg 插入 free list 的頭

tags: RT-Thread kernel ipc message queue