Android 内核代码 wake_up源码解析

    bool wakeup_condition; wait_queue_head_t wait_queue; init_waitqueue_head(&wait_queue); wait_queue_entry_t wq_entry // wait wait_event_interruptible(&wait_queue, wakeup_condition || kthread_should_stop()); // 唤醒 // 设置等待条件为true，并唤醒 wakeup_condition = true; wake_up(&wait_queue); 

// common/include/linux/wait.h #define TASK_NORMAL			(TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE) #define wake_up(x)			        __wake_up(x, TASK_NORMAL, 1, NULL) #define wake_up_interruptible(x)	__wake_up(x, TASK_INTERRUPTIBLE, 1, NULL) // common/kernel/sched/wait.c // wake_up 是个宏,展开后调用的是 __wake_up 函数 // __wake_up(x, TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE, 1, NULL) int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive, void *key) { return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key); } EXPORT_SYMBOL(__wake_up); // __wake_up_common_lock(wq_head, TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE, 1, 0, NULL) static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive, int wake_flags, void *key) { unsigned long flags; wait_queue_entry_t bookmark; int remaining = nr_exclusive; bookmark.flags = 0; bookmark.private = NULL; bookmark.func = NULL; INIT_LIST_HEAD(&bookmark.entry);//初始化链表: 链表的next和prev指针都指向链表自身地址 do { spin_lock_irqsave(&wq_head->lock, flags);//自旋锁上锁，对队列上锁 remaining = __wake_up_common(wq_head, mode, remaining, wake_flags, key, &bookmark); spin_unlock_irqrestore(&wq_head->lock, flags);//自旋锁解锁 } while (bookmark.flags & WQ_FLAG_BOOKMARK); return nr_exclusive - remaining;//队列为空时,remaining=nr_exclusive ,此时 return 0; } // __wake_up_common(wq_head, TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE, 1, 0, NULL, &bookmark); static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive, int wake_flags, void *key, wait_queue_entry_t *bookmark) { wait_queue_entry_t *curr, *next; int cnt = 0; lockdep_assert_held(&wq_head->lock); // bookmark.flags = 0;  WQ_FLAG_BOOKMARK = 0x04; if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {//不会进入此分支 curr = list_next_entry(bookmark, entry); list_del(&bookmark->entry); bookmark->flags = 0; } else curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);//获取wq_head队列的第一个元素 if (&curr->entry == &wq_head->head)//队列为空时,直接返回传入的 nr_exclusive return nr_exclusive; list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {//遍历链表 unsigned flags = curr->flags; int ret; if (flags & WQ_FLAG_BOOKMARK) continue; /* 调用 wait_queue_entry_t 中的回调函数 func //   这里依据func的类型会出现不同的结果。 使用 init_waitqueue_entry 初始化的 wait_queue_entry_t ，func = default_wake_function，这个函数会唤醒 curr->private 上的线程。 使用 init_waitqueue_func_entry 初始化的 wait_queue_entry_t，仅仅是做普通的函数调用。 */ ret = curr->func(curr, mode, wake_flags, key); if (ret <0) break; if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) break; if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) && (&next->entry != &wq_head->head)) { bookmark->flags = WQ_FLAG_BOOKMARK; list_add_tail(&bookmark->entry, &next->entry); break; } } return nr_exclusive; } 

//内核4.14以后 // common/include/linux/wait.h struct wait_queue_head {// wait队列 spinlock_t		lock;     // 自旋锁 struct list_head	head; // 添加到 wait 队列时,就是把wait_queue_entry.entry 加入这个 head 链表 }; /* * A single wait-queue entry structure: */ struct wait_queue_entry {// wait队列的一个项 unsigned int		flags; void			*private;   // 私有数据，在init_waitqueue_entry中代表线程，在init_waitqueue_func_entry中为null wait_queue_func_t	func;   // 回调函数 struct list_head	entry;  // 添加到 wait 队列时,就是把这个 entry 加入到 wait_queue_head.head 的链表 }; typedef struct wait_queue_head wait_queue_head_t;   // wait_queue_head_t  同 wait_queue_head typedef struct wait_queue_entry wait_queue_entry_t; // wait_queue_entry_t 同 wait_queue_entry 

// common/include/linux/wait.h static inline void init_waitqueue_entry(struct wait_queue_entry *wq_entry, struct task_struct *p) { wq_entry->flags		= 0; wq_entry->private	= p; // 把需要唤醒的线程存储到 private 数据中 // func 赋值为 default_wake_function 函数 // 这个函数的作用是 唤醒等待队列上的线程 wq_entry->func		= default_wake_function; // 这函数作用是：唤醒线程 p } static inline void init_waitqueue_func_entry(struct wait_queue_entry *wq_entry, wait_queue_func_t func) { wq_entry->flags		= 0; wq_entry->private	= NULL; wq_entry->func		= func; // 直接把传入的回调函数赋值给 wq_entry->func } 

int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags, void *key) { WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~WF_SYNC); //try_to_wake_up函数通过把进程状态设置为TASK_RUNNING, 并把该进程插入本地CPU运行队列rq来达到唤醒睡眠和停止的进程的目的. // curr->private 存储了需要唤醒的线程 return try_to_wake_up(curr->private, mode, wake_flags); } EXPORT_SYMBOL(default_wake_function); 

    bool wakeup_condition; wait_queue_head_t wait_queue; init_waitqueue_head(&wait_queue); wait_queue_entry_t wq_entry // wait 第一种用法：线程等待 wait_event_interruptible(&wait_queue, wakeup_condition || kthread_should_stop()); 第二种用法：添加一个回调到等待队列上 init_waitqueue_func_entry(&wq_entry, callback); add_wait_queue(&wait_queue, &wq_entry); // 唤醒 设置等待条件为true，并唤醒 wakeup_condition = true; // 内部遍历队列，调用每个 wait_queue_entry 的 func 函数，根据func不同为产生不同效果 wake_up(&wait_queue);