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Subject: Re: questions on wait_event ...
From: Steven Rostedt <rostedt@goodmis.org>
To: Alexey Shinkin <alexshinkin@hotmail.com>
Cc: linux-kernel@vger.kernel.org
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Date: Thu, 22 Dec 2005 20:10:40 -0500
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On Fri, 2005-12-23 at 06:51 +0600, Alexey Shinkin wrote:

> 
> And what if the condition have changed after we have checked it in 
> wait_event() but
> before calling __wait_event() and before putting the process into the wait 
> queue ?
> The process could not be woken up "in advance" , right ?

Lets add the other part of this too (the __wait_event)

#define __wait_event(wq, condition) 					\
do {									\
	DEFINE_WAIT(__wait);						\
									\
	for (;;) {							\
		prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE);	\
		if (condition)						\
			break;						\
		schedule();						\
	}								\
	finish_wait(&wq, &__wait);					\
} while (0)


> 
> 
> #define wait_event(wq, condition)        \
> do {                                                   \
>         if (condition)                                \
>                 break;                                 \
>    /* and here we have condition changed  ???? */
>         __wait_event(wq, condition);        \
> } while (0)
> 

So if the condition happens there, it will be checked again up above in
__wait_event.

-- Steve