5 获取信号量卡在rt_ipc_list_suspend()的问题

发布于 2021-10-15 11:24:05 浏览：1512 订阅该版

[tocm]

# RTT版本号
-  V4.0.3

# 问题描述
在使用rt_sem_take()函数进行信号量获取时，会卡死在如下函数(位于ipc.c)：
```c
/**
 * This function will suspend a thread to a specified list. IPC object or some
 * double-queue object (mailbox etc.) contains this kind of list.
 *
 * @param list the IPC suspended thread list
 * @param thread the thread object to be suspended
 * @param flag the IPC object flag,
 *        which shall be RT_IPC_FLAG_FIFO/RT_IPC_FLAG_PRIO.
 *
 * @return the operation status, RT_EOK on successful
 */
rt_inline rt_err_t rt_ipc_list_suspend(rt_list_t        *list,
                                       struct rt_thread *thread,
                                       rt_uint8_t        flag)
{
    /* suspend thread */
    rt_thread_suspend(thread);

switch (flag)
    {
    case RT_IPC_FLAG_FIFO:
        rt_list_insert_before(list, &(thread->tlist));
        break;

case RT_IPC_FLAG_PRIO:
        {
            struct rt_list_node *n;
            struct rt_thread *sthread;

/* find a suitable position */
            for (n = list->next; n != list; n = n->next)
            {
                sthread = rt_list_entry(n, struct rt_thread, tlist);

/* find out */
                if (thread->current_priority < sthread->current_priority)
                {
                    /* insert this thread before the sthread */
                    rt_list_insert_before(&(sthread->tlist), &(thread->tlist));
                    break;
                }
            }

/*
             * not found a suitable position,
             * append to the end of suspend_thread list
             */
            if (n == list)
                rt_list_insert_before(list, &(thread->tlist));
        }
        break;

default:
        break;  
    }

return RT_EOK;
}
```
具体是卡在31-42的for循环中，Debug发现for循环条件中，list变量的next和prev成员均为同一个，导致无限循环：
![image.png](https://oss-club.rt-thread.org/uploads/20211015/0e97a519c7995fecb3c4928dc9cc3fe8.png)

thread和sthread亦为同一个：
![image.png](https://oss-club.rt-thread.org/uploads/20211015/fc5557fa67125d36d705da6b27d7e241.png)