进程调度API之finish_wait

void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)用于结束wait queue 之后的清理工作，首先将当前函数的状态设置为TASK_RUNNING，如果第二个形参wait->task_list 不为null的话，则将wait->task_list 做置null，并重新对wait->task_list进行初始化其用法之前已经博文展示过了其源码分析如下：void finish_wait(wait_queue_head_t *q, wait_queue_t *wait){unsigned long flags;//将当前进程的状态设置为TASK_RUNNING__set_current_state(TASK_RUNNING);/* * We can check for list emptiness outside the lock * IFF: *  - we use the "careful" check that verifies both *    the next and prev pointers, so that there cannot *    be any half-pending updates in progress on other *    CPU's that we haven't seen yet (and that might *    still change the stack area. * and *  - all other users take the lock (ie we can only *    have _one_ other CPU that looks at or modifies *    the list). *///wait->task_list 不为null的话，则调用list_del_init删除这个list上的entry，并重新初始化if (!list_empty_careful(&wait->task_list)) {spin_lock_irqsave(&q->lock, flags);list_del_init(&wait->task_list);spin_unlock_irqrestore(&q->lock, flags);}}这里用list_empty_careful 来判断list是否为null。这个函数和list_empty相比检测更严格一点，个人感觉list_empty 适用用单向链表和list_empty_careful 适用于双向链表static inline int list_empty(const struct list_head *head){return READ_ONCE(head->next) == head;}通过code 对比很容易看出区别.static inline int list_empty_careful(const struct list_head *head){struct list_head *next = head->next;return (next == head) && (next == head->prev);}