RT-thread线程切换原理与实现

 RTThread官网看一下，可以发现【rt_thread_suspend】的函数说明中，特意的说明了这个函数不能通过A线程挂起B线程。

       翻开源码看一下，在这个函数中有这么一个判断，会判断需要挂起线程的状态，如果线程不等于就绪态那么就不会进入挂起，而sleep，delay等函数都会导致线程的挂起，那么其他线程想要挂起这个线程肯定会掉到这个if里面，从而挂起不了这个线程。

这里有两个解决思路，一个是通过 rt_thread_detach(&thread)删除线程的方法实现，另外一个就是定义一个暂停信号量，然后在需要暂停的线程中去不停的监测这个信号量，当接收到信号量时，自己主动挂起线程并让出CPU，这样就可以实现暂停线程，而且还能够知道线程暂停在哪，下面就第二个思路进行的代码实现如下：

#include 
ALIGN(RT_ALIGN_SIZE)
static rt_uint8_t a_thread_stack[ 512 ];
ALIGN(RT_ALIGN_SIZE)
static rt_uint8_t b_thread_stack[ 512 ];
ALIGN(RT_ALIGN_SIZE)
static rt_uint8_t c_thread_stack[ 512 ];
static struct rt_thread a_thread;
static struct rt_thread b_thread;
static struct rt_thread c_thread;
static rt_sem_t b_pause_sem = RT_NULL;
static rt_sem_t c_pause_sem = RT_NULL;
static void a_thread_entry(void *parameter)
{
   unsigned int count = 0;
   while (1)
   {
       count++;
       if(count == 10)
       {
           rt_kprintf("b start!\n");
           rt_thread_startup(&b_thread);   //开始扫地
       }
       else if(count == 30)
       {
           rt_kprintf("b pause!\n");
           rt_sem_release(b_pause_sem);//rt_thread_suspend(&b_thread);   //停止扫地
           rt_kprintf("c start!\n");
           rt_thread_startup(&c_thread);   //开始洗碗
       }
       else if(count == 50)
       {
           rt_kprintf("c pause!\n");
           rt_sem_release(c_pause_sem);//rt_thread_suspend(&c_thread);   //停止洗碗
           rt_kprintf("b start!\n");
           rt_thread_resume(&b_thread);    //开始扫地
       }
       rt_thread_delay(100);
   }
}
static void b_thread_entry(void *parameter)
{
   unsigned int count = 0;
   while (1)
   {
       rt_kprintf("b thread run!\n");
       rt_thread_delay(300);
       if(rt_sem_take(b_pause_sem, 0) == RT_EOK)
       {
           rt_thread_suspend(&b_thread);   //停止扫地
           rt_schedule();
       }
   }
}
static void c_thread_entry(void *parameter)
{
   unsigned int count = 0;
   while (1)
   {
       rt_kprintf("c thread run!\n");
       rt_thread_delay(100);
       if(rt_sem_take(c_pause_sem, 0) == RT_EOK)
       {
           rt_thread_suspend(&c_thread);   //停止扫地
           rt_schedule();
       }
   }
}
int pause_thread_init(void)
{
   rt_err_t result;
  
   b_pause_sem = rt_sem_create("b_pause", 0, RT_IPC_FLAG_PRIO);
  
   c_pause_sem = rt_sem_create("c_pause", 0, RT_IPC_FLAG_PRIO);
   /* init led thread */
   result = rt_thread_init(&a_thread,
                           "a_thread",
                           a_thread_entry,
                           RT_NULL,
                           (rt_uint8_t *)&a_thread_stack[0],
                           sizeof(a_thread_stack),
                           5,
                           5);
                          
   if (result == RT_EOK)
   {
       rt_thread_startup(&a_thread);
   }
  
   /* init led thread */
   result = rt_thread_init(&b_thread,
                           "b_thread",
                           b_thread_entry,
                           RT_NULL,
                           (rt_uint8_t *)&b_thread_stack[0],
                           sizeof(b_thread_stack),
                           6,
                           5);
                          
  
   /* init led thread */
   result = rt_thread_init(&c_thread,
                           "c_thread",
                           c_thread_entry,
                           RT_NULL,
                           (rt_uint8_t *)&c_thread_stack[0],
                           sizeof(c_thread_stack),
                           7,
                           5);
                          
   return 0;
}
/* 导出到 msh 命令列表中 */
MSH_CMD_EXPORT(pause_thread_init, pause thread);


　　审核编辑：汤梓红