kernel的sleep机制
一 。因为我是在写driver的时候,学会的这个问题,就以driver的代码来理解吧。
while (dev->rp == dev->wp) { /* nothing to read */
up(&dev->sem); /* release the lock */
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
PDEBUG("\"%s\" reading: going to sleep\n", current->comm);
if (wait_event_interruptible(dev->inq, (dev->rp != dev->wp)))
return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
/* otherwise loop, but first reacquire the lock */
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
}
这是driver的读的代码中,获取semaphore后,查看是否有信息可以读,如果没有就使用:
if (wait_event_interruptible(dev->inq, (dev->rp != dev->wp)))
return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
将自己挂起,直到写的proc调用:
/* finally, awake any reader */
wake_up_interruptible(&dev->inq); /* blocked in read() and select() */
将dev->inq中的进程全部都唤醒,并且移除inq。
二 manual sleep
while (spacefree(dev) == 0) { /* full */
DEFINE_WAIT(wait);
up(&dev->sem);
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
PDEBUG("\"%s\" writing: going to sleep\n",current->comm);
prepare_to_wait(&dev->outq, &wait, TASK_INTERRUPTIBLE);
if (spacefree(dev) == 0)
schedule();
finish_wait(&dev->outq, &wait);
if (signal_pending(current))
return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
}
return 0;
这里手动的使用如下的代码完成了wait_envent_interruptible:
DEFINE_WAIT(wait);
prepare_to_wait(&dev->outq, &wait, TASK_INTERRUPTIBLE);
if (spacefree(dev) == 0)
schedule();
finish_wait(&dev->outq, &wait);
if (signal_pending(current))
return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
也就是说wait_event_interruptible中传给他的验证条件只是为了这里的防止在schedule之前被唤醒。。这样就不用再进入schedule了。