about wait_event() ,wait_event_interruptible and wait_event_interruptible_timeout()

最新推荐文章于 2023-04-27 12:21:22 发布

原创最新推荐文章于 2023-04-27 12:21:22 发布 · 1.2k 阅读

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本文详细解析了Linux内核中的等待队列实现机制，包括__wait_event、wait_event、wait_event_interruptible及其带超时的版本等关键宏定义。通过这些宏定义可以深入理解进程在特定条件下如何进入等待状态，并在条件满足时被唤醒。

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all of those are condition=0 cause waiting!!!!!!

First, we can see the prototype in the kernel!!!

__wait_event!!!!!!!!!!!!

#define __wait_event(wq, condition)      /
do {         /
DEFINE_WAIT(__wait);      /
         /
for (;;) {     //  it    is  an  infinite loop!!!!!!!!

  prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); /
  if (condition)      /
   break;      /
  schedule();      /
}        /
finish_wait(&wq, &__wait);     /
} while (0)

wait_event!!!!!!!!!!!!!!!

#define wait_event(wq, condition) /
do { /
if (condition)//if condition is 0,waiting!!!!!!

break; /
__wait_event(wq, condition); /
} while (0)

wait_event_interruptible!!!

#define wait_event_interruptible(wq, condition)

{
int __ret = 0;
if (!(condition))
  __wait_event_interruptible(wq, condition, __ret);
__ret;
}

#define __wait_event_interruptible(wq, condition, ret)   /
do {         /
DEFINE_WAIT(__wait);      /
         /
for (;;) {       /
  prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); /
  if (condition)      /
   break;      /
  if (!signal_pending(current)) {

schedule(); /
   continue;     /
  }       /
  ret = -ERESTARTSYS;     /
  break;       /
}        /
finish_wait(&wq, &__wait);     /
} while (0)

#define wait_event_interruptible_timeout(wq, condition, timeout) /
({         /
long __ret = timeout;      /
if (!(condition))      /
  __wait_event_interruptible_timeout(wq, condition, __ret); /
__ret;        /
})

#define __wait_event_interruptible_timeout(wq, condition, ret)  /
do {         /
DEFINE_WAIT(__wait);      /
         /
for (;;) {       /
  prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); /
  if (condition)      /
   break;      /
  if (!signal_pending(current)) {    /if it is not wakened by a signal!!!!!!!

ret = schedule_timeout(ret); /a soft delay also schedule!!!!!

   if (!ret)     /
    break;     /
   continue;     /
  }       /
  ret = -ERESTARTSYS;     /
  break;       /
}        /
finish_wait(&wq, &__wait);     /
} while (0)