信号量官方示例一些疑问

发布于 2023-04-20 09:56:22 浏览：490 订阅该版

上面这段是官方信号量代码，如果我将线程优先级设置为3或4，实验效果与官方实验效果不一样。
```c
#include <rtthread.h>

#define THREAD_PRIORITY         25
#define THREAD_TIMESLICE        5

/* 指向信号量的指针 */
static rt_sem_t dynamic_sem = RT_NULL;

ALIGN(RT_ALIGN_SIZE)
static char thread1_stack[1024];
static struct rt_thread thread1;
static void rt_thread1_entry(void *parameter)
{
    static rt_uint8_t count = 0;

while(1)
    {
        if(count <= 100)
        {
            count++;
        }
        else
            return;

/* count 每计数 10 次，就释放一次信号量 */
         if(0 == (count % 10))
        {
            rt_kprintf("t1 release a dynamic semaphore.\n");
            rt_sem_release(dynamic_sem);
        }
    }
}

ALIGN(RT_ALIGN_SIZE)
static char thread2_stack[1024];
static struct rt_thread thread2;
static void rt_thread2_entry(void *parameter)
{
    static rt_err_t result;
    static rt_uint8_t number = 0;
    while(1)
    {
        /* 永久方式等待信号量，获取到信号量，则执行 number 自加的操作 */
        result = rt_sem_take(dynamic_sem, RT_WAITING_FOREVER);
        if (result != RT_EOK)
        {
            rt_kprintf("t2 take a dynamic semaphore, failed.\n");
            rt_sem_delete(dynamic_sem);
            return;
        }
        else
        {
            number++;
            rt_kprintf("t2 take a dynamic semaphore. number = %d\n" ,number);
        }
    }
}

/* 信号量示例的初始化 */
int semaphore_sample(void)
{
    /* 创建一个动态信号量，初始值是 0 */
    dynamic_sem = rt_sem_create("dsem", 0, RT_IPC_FLAG_PRIO);
    if (dynamic_sem == RT_NULL)
    {
        rt_kprintf("create dynamic semaphore failed.\n");
        return -1;
    }
    else
    {
        rt_kprintf("create done. dynamic semaphore value = 0.\n");
    }

rt_thread_init(&thread1,
                   "thread1",
                   rt_thread1_entry,
                   RT_NULL,
                   &thread1_stack[0],
                   sizeof(thread1_stack),
                   THREAD_PRIORITY, THREAD_TIMESLICE);
    rt_thread_startup(&thread1);

rt_thread_init(&thread2,
                   "thread2",
                   rt_thread2_entry,
                   RT_NULL,
                   &thread2_stack[0],
                   sizeof(thread2_stack),
                   THREAD_PRIORITY-1, THREAD_TIMESLICE);
    rt_thread_startup(&thread2);

return 0;
}
/* 导出到 msh 命令列表中 */
MSH_CMD_EXPORT(semaphore_sample, semaphore sample);

```