进程调度API之__wake_up_sync

void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)和__wake_up 函数的形参和作用一样。不同在于会根据是如果nr_exclusive等于1的话，传递给wakup 后要执行函数的wake_flags 等于1.而__wake_up 传递的wake_flags always是0void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive){__wake_up_sync_key(q, mode, nr_exclusive, NULL);}可以看到__wake_up_sync_key 最后一个参数是nullvoid __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,int nr_exclusive, void *key){unsigned long flags;int wake_flags = 1; /* XXX WF_SYNC */if (unlikely(!q))return;#如果nr_exclusive 等于1的话，这里的wake_flags 就是1if (unlikely(nr_exclusive != 1))wake_flags = 0;spin_lock_irqsave(&q->lock, flags);#__wake_up 和 __wake_up_sync 最终都会调用__wake_up_common，其区别就在第四个参数，#__wake_up 调用__wake_up_common的时候wake_flags 这个形参always是0.但是__wake_up_sync #调用的时候，这个参数大部分情况下是1__wake_up_common(q, mode, nr_exclusive, wake_flags, key);spin_unlock_irqrestore(&q->lock, flags);}static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,int nr_exclusive, int wake_flags, void *key){wait_queue_t *curr, *next;list_for_each_entry_safe(curr, next, &q->task_list, task_list) {unsigned flags = curr->flags;if (curr->func(curr, mode, wake_flags, key) &&(flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)break;}}最终wake_flags 会传递给用户自己定义的wakeup的callback函数，这个wake_flags的意义就在于用户可以根据这个是0还是1判断当前thread是否被独占.