On 06/05, Imre Deak wrote:
>
> On Wed, 2013-06-05 at 00:35 +0300, Imre Deak wrote:
> > On Tue, 2013-06-04 at 21:28 +0200, Oleg Nesterov wrote:
> > >
> > > Shouldn't we also change wait_event_timeout() ? Say,
> > >
> > > #define wait_event_timeout(wq, condition, timeout)
> > > \
> > > ({
> > > \
> > > long __ret = timeout;
> > > \
> > > if (!(condition))
> > > \
> > > __wait_event_timeout(wq, condition, __ret);
> > > \
> > > else if (!__ret)
> > > \
> > > __ret = 1;
> > > \
> > > __ret;
> > > \
> > > })
> > >
> > > Or wait_event_timeout(timeout => 0) is not legal in a non-void context?
> > >
> > > To me the code like
> > >
> > > long wait_for_something(bool nonblock)
> > > {
> > > timeout = nonblock ? 0 : DEFAULT_TIMEOUT;
> > > return wait_event_timeout(..., timeout);
> > > }
> > >
> > > looks reasonable and correct. But it is not?
> >
> > I don't see why it would be not legal. Note though that in the above
> > form wait_event_timeout(cond, 0) would still schedule() if cond is
> > false, which is not what I'd expect from a non-blocking function.
Yes, if false. But what if it is true?
> Ah sorry, if you also rewrite __wait_event_timeout() then timeout=>0
> wouldn't schedule(), so things would work as expected.
Can't understand... probably you missed my point. Let me try again.
I think that wait_eveint_timeout(wq, COND, 0) should return !!(COND).
But it doesn't, for example wait_event_timeout(wq, true, 0) == 0, this
doesn'tlook right to me.
And, this is off-topic, but wait_eveint_timeout/__wait_eveint_timeout
do not match wait_event/__wait_event. IOW, you can't use
__wait_eveint_timeout() if you do not need the fast-path check.
So. How about
#define __wait_event_timeout(wq, condition, timeout)
\
({
\
DEFINE_WAIT(__wait);
\
long __ret = 0, __to = timeout;
\
\
for (;;) {
\
prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE);
\
if (condition) {
\
__ret = __to ?: 1;
\
break;
\
}
\
if (!__to)
\
break;
\
__to = schedule_timeout(__to);
\
}
\
finish_wait(&wq, &__wait);
\
__ret;
\
})
#define wait_event_timeout(wq, condition, timeout)
\
({
\
long __ret;
\
if (condition)
\
__ret = (timeout) ?: 1;
\
else
\
__ret = __wait_event_timeout(wq, condition, timeout);
\
__ret;
\
})
?
Othwerwise we should document the fact that the caller should alvays verify
timeout != 0 if it checks the result of wait_event_timeout().
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