1 消息队列
消息队列是一种常用的线程间异步通讯方式；
消息队列能够接收来自线程或中断中不固定长度的消息，并把消息缓存在自己的内存空间中，供线程间进行异步通讯；
1.1 结构体定义
//rtconfig.h 源码默认注释掉未开启，用到消息队列的时候需要自己开启；
#define RT_USING_MESSAGEQUEUE
//rtdef.h
#ifdef RT_USING_MESSAGEQUEUE
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
//rtdef.h suspend_thread在create函数中初始化，作为suspend线程的链表节点来挂载;
struct rt_ipc_object
{
struct rt_object parent; /**< inherit from rt_object */
rt_list_t suspend_thread; /**< threads pended on this resource */
};
//ipc.c 和rt_mq_init()函数一起定义的;
//rt_mq_init()静态创建mq结构体，rt_mq_create()动态创建mq结构体;demo里用的动态创建的;
#ifdef RT_USING_MESSAGEQUEUE
struct rt_mq_message
{
struct rt_mq_message *next;
};1.2 rt_mq_create 消息队列初始化
分配rt_messagequeue结构体内存，初始化以及分配空闲链表消息池；
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));
/* init message queue */
/* get correct message size */
mq->msg_size = RT_ALIGN(msg_size, RT_ALIGN_SIZE);
mq->max_msgs = max_msgs;
/* allocate message pool (消息size + messagenext链表)*消息个数 */
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;
}
/* 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 mq;
}
RTM_EXPORT(rt_mq_create);1.3 rt_mq_send 消息队列发送
从空闲msg_pool中取出msg_queue_free链表，然后插入到消息msg_pool中等待发送；
如果mq->parent.suspend_thread不为空，则把suspend_thread从suspend_list中删除之后然后再挂载回优先级表中启动调度；
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;
RT_ASSERT(mq != RT_NULL);
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; //msg: &head2;
/* 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; //msg_queue_free: &head1;
/* enable interrupt */
rt_hw_interrupt_enable(temp);
/* the msg is the new tailer of list, the next shall be NULL */
msg->next = RT_NULL; //msg->next:null,不知道为什么要清空，因为作为一个新的消息等会用来插入msg_pool中;
/* copy buffer */
rt_memcpy(msg + 1, buffer, size); //将消息存入msg_size大小的空间中,不知道为什么要加1，这里已经是新消息的地址啦;
/* 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;
}
/* 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;
/* 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_send);1.4 rt_mq_recv消息队列接收
从消息队列中取出数据，然后把取出数据的消息地址放回空闲池里；
//ipc.c
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;
RT_ASSERT(mq != RT_NULL);
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 如果消息队列中没有消息且不等待消息，就直接返回;*/
if (mq->entry == 0 && timeout == 0)
{
rt_hw_interrupt_enable(temp);
return -RT_ETIMEOUT;
}
/* message queue is empty 如果消息队列中没有消息，通过timeout判断是否等待处理;*/
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;
}
/* suspend current thread */
rt_ipc_list_suspend(&(mq->parent.suspend_thread),
thread,
mq->parent.parent.flag);
/* 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));
}
/* enable interrupt */
rt_hw_interrupt_enable(temp);
/* re-schedule */
rt_schedule();
/* 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;
}
}
/* get message from queue **********先放着，**************************/
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;
/* decrease message entry */
mq->entry --;
/* enable interrupt */
rt_hw_interrupt_enable(temp);
/* copy message 发送函数中msg地址加1不理解，不过这里也+1回去了,只是觉得没必要;*/
rt_memcpy(buffer, msg + 1, size > mq->msg_size ? mq->msg_size : size);
/* disable interrupt */
temp = rt_hw_interrupt_disable();
/* put message to free list 将用完的消息地址放回空闲池;存放方式类似堆栈push和pop; */
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);1.5 收发消息队列图
不知道为什么用memcpy( )的时候收发的msg 地址都加1了，我觉得那里分配的地址应该不需要加1的，可是不加1会报错，先放着吧，以后再说；
1.6 suspend_thread链表节点
//在rt_mq_send函数中，发送数据的时候，储存完数据之后会把suspend_thread恢复；
/* 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;
}
//在rt_mq_recv函数中，接收数据的时候，会先把当前thread挂载到suspend_thread链表节点下;
/* suspend current thread */
rt_ipc_list_suspend(&(mq->parent.suspend_thread),
thread,
mq->parent.parent.flag);
//这个信息是如何在两个线程间传递的，我有一点不理解，先放着吧；2 小结
每次分配地址和数据的时候分界点的边界总是有点迷糊，都得重新找一遍规律，这样不行呀；
指针向下移动第几个，就是移动到第几位地址；[0]+5 = [5]，[2]+5 = [7]；msg_pool的地址从head头移动到head尾，要+1才到下面消息地址；
接收里有好几个if(timeout>0),也不知道都有啥用；
parent.suspend_thread的处理流程是怎么样的呢？