用信号量做线程同步的一个小问题

发布于 2021-10-19 22:19:37 浏览：977 订阅该版

3 个回答

出出啊 2021-10-20

恃人不如自恃，人之为己者不如己之自为也

李肯陪你玩赚嵌入式 认证专家 2021-10-20

2022年度和2023年度RT-Thread社区优秀开源布道师，COC深圳城市开发者社区主理人，专注于嵌入式物联网的架构设计

根据RRT对[rt_sem_take接口的介绍](https://docs.rt-thread.org/#/rt-thread-version/rt-thread-standard/programming-manual/ipc1/ipc1?id=%e4%bf%a1%e5%8f%b7%e9%87%8f)：
![image.png](https://oss-club.rt-thread.org/uploads/20211020/a34811a4dffab556e2b98d77af82f855.png.webp)
以及源码里面的注释介绍：
```
/**
 * @brief    This function will take a semaphore, if the semaphore is unavailable, the thread shall wait for
 *           the semaphore up to a specified time.
 *
 * @note     When this function is called, the count value of the sem->value will decrease 1 until it is equal to 0.
 *           When the sem->value is 0, it means that the semaphore is unavailable. At this time, it will suspend the
 *           thread preparing to take the semaphore.
 *           On the contrary, the rt_sem_release() function will increase the count value of sem->value by 1 each time.
 *
 * @see      rt_sem_trytake()
 *
 * @param    sem is a pointer to a semaphore object.
 *
 * @param    time is a timeout period (unit: an OS tick). If the semaphore is unavailable, the thread will wait for
 *           the semaphore up to the amount of time specified by the argument.
 *           NOTE: Generally, we use the macro RT_WAITING_FOREVER to set this parameter, which means that when the
 *           semaphore is unavailable, the thread will be waitting forever.
 *
 * @return   Return the operation status. ONLY When the return value is RT_EOK, the operation is successful.
 *           If the return value is any other values, it means that the semaphore take failed.
 *
 * @warning  This function can ONLY be called in the thread context. It MUST NOT BE called in interrupt context.
 */
rt_err_t rt_sem_take(rt_sem_t sem, rt_int32_t time)
```
![image.png](https://oss-club.rt-thread.org/uploads/20211020/951c45c8774ffabc1956f5d3967c4052.png.webp)

我猜测你这种情况是一个接口返回error了，而不是ok，你可以使用int变量接收下这个接口的返回值。
还有一定，看你打印的brew_sem.value值为0，证明信号量此时是空的（大于0表示有信号量）。
还有办法，你可以把RT_DEBUG_IPC宏打开（rtdebug.h）,调试下这个接口，我看到都有关键的log打印。