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 [email protected]
Home Page: http://www.roberthancock.com/
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 ?
#define wait_event(wq, condition) \
do { \
if (condition) \
break; \
/* and here we have condition changed ???? */
__wait_event(wq, condition); \
} while (0)
Regards
Alexey Shinkin
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