睡眠--TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE

6. Now that the condition is true, the task can set itself to TASK_RUNNING and remove itself from the wait queue via remove_wait_queue().
|--------------------|
|set_current_state(TASK_RUNNING); ? ? ? ? ? ? ?|
|remove_wait_queue(q, &wait); ? ? ? ? ? ? ? ? ? ? |
|--------------------|
? ? If the condition occurs before the task goes to sleep, the loop terminates, and the task does not erroneously go to sleep. Note that kernel code often has to perform various other tasks in the body of the loop. For example, it might need to release locks before calling schedule() and reacquire them after or react to other events.?
? ? 如果在进程开始睡眠之前条件就已经达成了，那么循环会退出，进程不会存在错误的进入休眠的倾向。需要注意的是，内核代码在循环体内常常需要完成一些其他的任务，比如，它可能在调用schedule()之前需要释放掉锁，而在这以后再重新获取它们，或者响应其他的事件。
? ? Waking is handled via wake_up(), which wakes up all the tasks waiting on the given wait queue. It calls try_to_wake_up(), which sets the task's state to TASK_RUNNING, calls activate_task() to add the task to a runqueue, and sets need_resched if the awakened task's priority is higher than the priority of the current task. The code that causes the event to occur typically calls wake_up() afterward.?
? ? 唤醒操作通过函数wake_up进行，它会唤醒指定的等待队列上的所有进程。它调用函数try_to_wake_up，该函数负责将进程设置为TASK_RUNNING状态，调用activate_task将此进程放入可执行队列，如果被唤醒的进程优先级比当前正在运行的进程的优先级高，还有设置need_resched标志。通常哪段代码促使等待条件达成，它就负责随后调用wake_up()函数。?
? ? An important note about sleeping is that there are spurious wake-ups. Just because a task is awakened does not mean that the event for which the task is waiting has occurred; sleeping should always be handled in a loop that ensures that the condition for which the task is waiting has indeed occurred.?
? ? 关于休眠有一点需要注意，存在虚假的唤醒。有时候进程被唤醒并不是因为它所等待的条件达成了(而是接受到了信号)，所以才需要用一个循环处理来保证它等待的条件真正达成。?


[b]本文来自ChinaUnix博客，如果查看原文请点：http://www.cnblogs.com/parrynee/archive/2010/01/14/1648165.html