# RT-Thread IPC Scheduler lock

rt_enter_critical()
    /*
     *  critical region 
     */
rt_exit_critical()

- 使用此方式可確保當前 thread 不會被 scheduler 踢出，但還是有可能會被中斷影響。

---
## 進入 scheuler 鎖
:::success
**File:** scheduler.c
:::
### `rt_enter_critical`

| 功能 | 回傳值 |
| --- | ------ |
| 進入 scheuler 鎖 | void |

/**
 * This function will lock the thread scheduler.
 */
void rt_enter_critical(void)
{
    register rt_base_t level;

    /* disable interrupt */
    level = rt_hw_interrupt_disable();

    /*
     * the maximal number of nest is RT_UINT16_MAX, which is big
     * enough and does not check here
     */
    rt_scheduler_lock_nest ++;

    /* enable interrupt */
    rt_hw_interrupt_enable(level);
}
RTM_EXPORT(rt_enter_critical);

- 即，將 `rt_scheduler_lock_nest` 加一

---
## 離開 scheduler 鎖
### `rt_exit_critical`

| 功能 | 回傳值 |
| --- | ------ |
| 離開 scheuler 鎖 | void |

/**
 * This function will unlock the thread scheduler.
 */
void rt_exit_critical(void)
{
    register rt_base_t level;

    /* disable interrupt */
    level = rt_hw_interrupt_disable();

    rt_scheduler_lock_nest --;

- 即，將 `rt_scheduler_lock_nest` 減一

    if (rt_scheduler_lock_nest <= 0)
    {
        rt_scheduler_lock_nest = 0;
        /* enable interrupt */
        rt_hw_interrupt_enable(level);

        rt_schedule();
    }
    else
    {
        /* enable interrupt */
        rt_hw_interrupt_enable(level);
    }
}

- 如果 `rt_scheduler_lock_nest` 被減至 0 或以下，進行一次調度

---
### `rt_critical_level`

| 功能 | 回傳值 |
| --- | ------ |
| 回傳 scheuler 鎖的值 | scheuler 鎖的值 |

/**
 * Get the scheduler lock level
 *
 * @return the level of the scheduler lock. 0 means unlocked.
 */
rt_uint16_t rt_critical_level(void)
{
    return rt_scheduler_lock_nest;
}
RTM_EXPORT(rt_critical_level);

- 即，回傳 `rt_scheduler_lock_nest` 值

###### tags: `RT-Thread` `kernel` `ipc`