Re: regarding __wait_event_interruptible

July 2, 2011

      On Fri, Jul 1, 2011 at 5:43 PM, Amit Nagal <helloin.amit@gmail.com> wrote:
...
instead why not prepare_to_wait() be used once only like finish_wait()
above and after schedule() call returns ,
set the current state = TASK_INTERRUPTIBLE (before continue statement
) something like below :
#define __wait_event_interruptible(wq, condition, ret)                  \
do {                                                                    \
       DEFINE_WAIT(__wait);                                            \
       prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE);              \
                                                                       \
       for (;;) {                                                      \
               if (condition)                                          \
                       break;                                          \
               if (!signal_pending(current)) {                         \
                       schedule();                                     \
               set_current_state(TASK_INTERRUPTIBLE)           \
                       continue;                                       \
               }                                                       \
               ret = -ERESTARTSYS;                                     \
               break;                                                  \
       }                                                               \
       finish_wait(&wq, &__wait);                                      \
} while (0)
kindly share facts related to above .
Regards
Amit Nagal
Reframing the above question , what i want to ask is while waiting for
wake up events or signals in a loop ,
do we need to call prepare_to_wait  in every iteration of the loop (case 1 ) or
we should call prepare_to_wait  once only before entring the loop
and after schedule call returns set the current state =
TASK_INTERRUPTIBE (case 2) .

both cases are detailed below :

case 1 :

for(;;){
prepare_to_wait( &wq , &wait , TASK_INTERRUPTIBLE )
if(condition) break ;

if(! signal_pending ) {
    schedule();
    continue ;
}

ret = -ERESTARTSYS;
  break;

}

finish_to_wait(&wq , &wait ) ;

case 2 :

prepare_to_wait( &wq , &wait , TASK_INTERRUPTIBLE )

for(;;){
if(condition) break ;

if(! signal_pending ) {
    schedule();
    set_current_state(TASK_INTERRUPTIBLE);
    continue ;
}

ret = -ERESTARTSYS;
  break;

}

finish_to_wait(&wq , &wait ) ;

please let me know whether implementing wait as in case 2 is right approach ?

Regards
Amit Nagal