Re: [dpdk-dev] [PATCH v2] Change alarm cancel function to thread-safe:

["Wodkowski, PawelX" <pawelx.wodkowski@intel.com>]

> Yes, this is my concern exactly.
> 
> >  If that's so, then I suppose we can do: make alarm_cancel() to return a
> negative value for the case #3 (-EINPROGRESS or something).
> >  Something like:
> > ...
> > if (ap->executing == 0) {
> >    LIST_REMOVE(ap,next);
> >     rte_free(ap);
> >     count++;
> >     ap = ap_prev;
> > } else if (pthread_equal(ap->executing_id, pthread_self()) == 0) {
> >     executing++;
> > } else {
> >    ret = -EINPROGRESS;
> > }
> > ...
> > return ((ret != 0) ? ret : count);
> >
> > So the return value  will be > 0 for #1, 0 for #2, <0 for #3.
> > As I remember, you already suggested something similar in one of the previous
> mails.
> Yes, I rolled the API changes I suggested in with this model, because I wanted
> to be able to do precise specification of a timer instance to cancel, but if
> we're not ready to make that change, I think what you propose above would be
> suffficient.  Theres some question as to weather we would cancel timers that
> are
> still pending on a return of -EINPROGRESS, but I think if we document it
> accordingly, then it can be worked out just fine.
> 
> Best
> Neil
> 

Image how you will be damned by someone that not even notice you change
and he Is managing some kind of resource based on returned number of 
set/canceled timers. If you suddenly start returning negative values how those
application will behave? Silently changing returned value domain is evil in its 
pure form.

>From my point of view, problem is virtual because this is user application task to 
know what it can and what it not. If you really want to inform user application
about timer state you can introduce API call which will interrogate timers list
and return appropriate value, but for god sake, do not introduce untraceable bugs.

Pawel