create_new_thread()调用后为什么内存没被释放掉？

static rt_thread_t new_thread = NULL;
void new_thread_entry(void* parameter)
{
    rt_thread_mdelay(2500);
    func();
    rt_thread_delete(new_thread);
}
void create_new_thread(void)
{
    // 创建一个新线程，优先级为15，时间片为10
    new_thread = rt_thread_create("new_thread", new_thread_entry, RT_NULL, 1024, 15, 10);
    if (new_thread != RT_NULL)
    {
        // 设置线程为自动释放
        rt_thread_startup(new_thread); 
    }   
}