关于wait_event_timeout

关于wait_event_timeout

标签（空格分隔）： 等待队列

http://bbs.chinaunix.net/thread-3615327-1-1.html

do {

DEFINE_WAIT(__wait);

for (;;) { // break可以退出

prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE);

if (condition)

break;

ret = schedule_timeout(ret);

if (!ret) /若timeout为等完，则进入下一次循环继续等 /

break; //若timeout超时，退出 */

} \

finish_wait(&wq, &__wait);

schedule_timeout有两种情况退出：

1. wake_up；

2. timer超时；

wake_up会把schedule_timeout打断，此时schedule_timeout注册的定时器并未超时，schedule_timeout直接返回，回到for(;循环，这个循环只有break才能推出，而break有两种情况：

1. 条件为真；

2. ret==0，也就是超时；

如果调用wake_up而condition不为真，则再次调用schedule_timeout，不过此时传入的时间，是上次剩余的时间，当其超时时，wait_event_timeout同样会执行到break退出，所以不会无限的执行下去：

/**

* wait_event_timeout - sleep until a condition gets true or a timeout elapses

* @wq: the waitqueue to wait on

* @condition: a C expression for the event to wait for

* @timeout: timeout, in jiffies

*

* The process is put to sleep (TASK_UNINTERRUPTIBLE) until the

* @condition evaluates to true. The @condition is checked each time

* the waitqueue @wq is woken up.

*

* wake_up() has to be called after changing any variable that could

* change the result of the wait condition.

*