Re: Empty events lists

As long as the error message is clear, I think this is the best route. Another way to consider this is: Will this result in hard to debug situations and will we see more questions on the systemc_forum? If the answer is yes, then we've done poorly. Bad enough that we have these confusions. I think an error exception is the safest way to avoid this corner case becoming a nightmare.

On Nov 2, 2010, at 1:51 PM, john.aynsley@doulos.com wrote:

> All,
>
> Okay, so I propose that wait(empty_list) and wait(delay, empty_list) are both errors. Agreed?
>
> (But otherwise I could live with Bishnupriya's error/warning proposal)
>
> John A
>
> -----"Philipp A. Hartmann" <philipp.hartmann@offis.de> wrote: -----
> To: john.aynsley@doulos.com
> From: "Philipp A. Hartmann" <philipp.hartmann@offis.de>
> Date: 11/02/2010 09:45AM
> Cc: p.goel@acm.org, david.long@doulos.com, P1666 Technical WG <systemc-p1666-technical@eda.org>
> Subject: Re: Empty events lists
>
> John, All
>
> since wait() typically means 'wait for static sensitivity, if present',
> 'wait(empty_list)' should at least NOT degenerate to 'wait()'.
>
> If we really want to add some semantics, I think we definitely need to
> warn the user to avoid accidental confusion. So to combine this with
> Puneet's proposal, this could mean:
>
> wait( empty_or_list ) => warn and wait forever
> (Any event fired? No. => Wait)
> wait( empty_and_list ) => warn and return immediately
> (All events fired? Yes. => Return)
>
> wait( delay, empty_or_list ) => warn and wait( delay )
> wait( delay, empty_and_list ) => warn and return immediately
>
> But maybe it's easier to simply error out in all cases, since the user
> can easily work around this as shown in my earlier mail. I tend to
> prefer this.
>
> Greetings from Oldenburg,
> Philipp
>
> On 02/11/10 17:30, john.aynsley@doulos.com wrote:
> > Puneet, Bishnupriya, All,
> >
> > I too understand what Puneet is saying. But SystemC event lists are not lists in a functional programming sense, and the typical SystemC user is not a functional programmer. On the other hand, there are existing semantics and clear expectations attached to wait(), i.e. it means wait forever.
> >
> > So, now we introduce explicit wait lists, allowing constructs such as wait(list) or wait(delay, list). If the list is empty, I think for SystemC users there are 3 obvious choices we could make
> >
> > - wait(empty_list) => wait forever
> > - wait(empty_list) => error
> > - wait(empty_list) => warning and wait forever
> >
> > Bisnupriya has proposed
> > - wait(empty_list) => error
> > - wait(delay, empty_list) => warning and wait(delay)
> >
> > I am not entirely comfortable with having the first as an error and the second as a warning. It's not a show-stopper for me, but if we are not going to have wait(empty_list) wait forever, then I would prefer both forms to be an error. It seems more straightforward.
> >
> > John A
> >
> >
> >
> > -----puneet@coverify.com wrote: -----
> > To: "Philipp A. Hartmann" <philipp.hartmann@offis.de>
> > From: Puneet Goel
> > Sent by: puneet@coverify.com
> > Date: 11/02/2010 04:11AM
> > Cc: david.long@doulos.com, john.aynsley@doulos.com, owner-systemc-p1666-technical@eda.org, systemc-p1666-technical@eda.org
> > Subject: Re: Empty events lists
> >
> >> It is like when you define an operation on a list, you start with a
> >> seed.
> >
> > Like in case of summation on a list you start with the result seeded
> > to 0. In case of multiplication (factorial) you start with the result
> > seeded to 1. In case of ORing a list, we start with the result seeded
> > to false. And in case of ANding a list, we start with the result
> > seeded to true.
> >
> > Similarly is we think about sc_event_and_list, we would seed the
> > result with an immediate event. And for sc_event_or_list, we should
> > seed the result with an event that never gets notified.
> >
> > Regards
> > - Puneet
> >
> >
> >
>
>
> --
> Philipp A. Hartmann
> Hardware/Software Design Methodology Group
>
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