Re: questions on wait_event ...

[Robert Hancock <hancockr@shaw.ca>]

Alexey Shinkin wrote:
> Hi , all !
> Could anyone please clarify one thing in that old well known
> wait_event_... code (taken from 2.6.5 wait.h ):
>
> #define __wait_event_interruptible(wq, condition, ret)          \
> do {                                                                    \
>        wait_queue_t __wait;                                     \
>        init_waitqueue_entry(&__wait, current);           \
>                                                                        \
>        add_wait_queue(&wq, &__wait);                   \
>        for (;;) {                                                      \
>                set_current_state(TASK_INTERRUPTIBLE);    \
>                if (condition)                                          \
>                        break;
> ........................................
>
> Is it possible that scheduling happen after set_current_state() but before
> checking the condition ?
> If yes - even if we will have condition==TRUE by this moment - the 
> scheduler
> will make the process to sleep anyway , right ?

Yes, but since the condition would then have changed after we were put 
into the wait queue, they would have woken up the queue and we should be 
woken up again.

--
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

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