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
OFFIS Institute for Information Technology
R&D Division Transportation · FuE-Bereich Verkehr
Escherweg 2 · 26121 Oldenburg · Germany
Phone/Fax: +49-441-9722-420/282 · PGP: 0x9161A5C0 · http://www.offis.de/
-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.