Re: Children of dead processes

John,

sounds good to me.

P.

On 13/01/11 10:05, john.aynsley@doulos.com wrote:
> Philipp, Bishnupriya,
>
> Yes, I think we are on the same page.
>
> Currently, the LRM says (under bool terminated() const) : "When the
> underlying process instance terminates, an implementation may choose to
> invalidate any associated process handles but is not obliged to do so."
>
> The LRM also says "However, if an implementation chooses to invalidate a
> process handle, it shall invalidate every process handle associated with
> the underlying process instance at that time. In other words, it shall not
> be possible to have a valid and an invalid handle to the same underlying
> process instance in existence at the same time."
>
> So given the existence of
> explicit sc_process_handle( sc_object* );
>
> we could choose to infer that in the case where a process object continues
> to exist only because it has surviving children, then the implementation
> is obliged to keep any process handles valid, even after the process
> instance has terminated.
>
> Does that work?
>
> John A
>
>
>
>
> From:
> "Philipp A. Hartmann" <philipp.hartmann@offis.de>
> To:
> john.aynsley@doulos.com
> Cc:
> Bishnupriya Bhattacharya <bpriya@cadence.com>,
> "systemc-p1666-technical@eda.org" <systemc-p1666-technical@eda.org>
> Date:
> 12/01/2011 17:25
> Subject:
> Re: Children of dead processes
>
>
>
> John,
>
> is there any reason to invalidate a process handle, if the underlying
> process object continues to exist (and logically points to the same
> instance, i.e. is not yet re-used)?
>
> I would even prefer to allow the deletion of such parent objects over
> having this mismatch between child.get_parent_object() and invalidated
> handles.
>
> From an implementation POV, one could still create new handles via
> sc_process_handle( child.get_parent_object() ), right? We would then
> have to make it implementation-defined, if handles of terminated
> processes can be created.
>
> Greetings from Oldenburg,
> Philipp
>
> On 12/01/11 17:54, john.aynsley@doulos.com wrote:
>>
>> Indeed. An implementation may choose to invalidate any process handles
> as
>> soon as a process instance terminates. In the case of a terminated
> process
>> with children, we have to decide whether the implementation is obliged
> to
>> keep any process handles valid as long as the process object continues
> to
>> exists. Otherwise we may have the situation where there exists a
>> non-terminated child process whose parent process continues to exist but
>
>> has an invalid handle. I do not see this is a problem, but it does seem
> a
>> little odd.
>>
>> John A
>>
>>
>>
>>
>> From:
>> "Philipp A. Hartmann" <philipp.hartmann@offis.de>
>> To:
>> john.aynsley@doulos.com
>> Cc:
>> Bishnupriya Bhattacharya <bpriya@cadence.com>,
>> "systemc-p1666-technical@eda.org" <systemc-p1666-technical@eda.org>
>> Date:
>> 12/01/2011 14:53
>> Subject:
>> Re: Children of dead processes
>>
>>
>>
>> Yes, exactly.
>>
>> Additionally, this has implications for the invalidation of process
>> handles as well, right?
>>
>> Philipp
>>
>> On 12/01/11 13:49, john.aynsley@doulos.com wrote:
>>> Bishnupriya, Philipp,
>>>
>>> Agreed. So as I understand it, we are proposing that for every
>> occurrence
>>> of get_parent_object() in the LRM, we change the description to say
> that
>>
>>> the following:
>>>
>>> If the parent object is a process instance and that process has
>>> terminated, get_parent_object shall return a pointer to the process
>>> instance. The parent process instance shall not be deleted while the
>>> process instance has child objects, but may be deleted once all its
>> child
>>> objects have been deleted
>>>
>>> Right?
>>>
>>> John A
>>>
>>>
>>>
>>> From:
>>> Bishnupriya Bhattacharya <bpriya@cadence.com>
>>> To:
>>> "john.aynsley@doulos.com" <john.aynsley@doulos.com>,
>>> "philipp.hartmann@offis.de" <philipp.hartmann@offis.de>,
>>> "systemc-p1666-technical@eda.org" <systemc-p1666-technical@eda.org>
>>> Date:
>>> 11/01/2011 18:14
>>> Subject:
>>> RE: Children of dead processes
>>>
>>>
>>>
>>> John,
>>>
>>> Philip raises excellent questions, and I?m very much in favor of
>> mandating
>>> that parent process objects with live children should not be deleted.
> It
>>
>>> provides a nice, clean, intuitive semantics with no ?surprises? for the
>
>>> user.
>>>
>>> Thanks,
>>> -Bishnupriya
>>>
>>> From: john.aynsley@doulos.com [mailto:john.aynsley@doulos.com]
>>> Sent: Tuesday, January 11, 2011 6:04 PM
>>> To: Bishnupriya Bhattacharya; philipp.hartmann@offis.de;
>>> systemc-p1666-technical@eda.org
>>> Subject: Children of dead processes
>>>
>>> All,
>>>
>>> Philipp has raised the following issues:
>>>
>>>
>>> 6.6.5 sc_process_handle::get_parent_object
>>> 6.16.7 sc_object::get_parent_object
>>>
>>> "If the parent object is a process instance and that process has
>>> terminated, get_parent_object shall return either a pointer to the
>>> surviving process instance or a null pointer if it has been deleted."
>>>
>>> What happens to the object's position itself, when the parent object
> is
>>
>>> NULL?
>>>
>>> - It can still be found via sc_find_object( obj.name() )?
>>>
>>> - Is it moved to the top-level, i.e. can it be found via
>>> sc_get_top_level_objects()?
>>>
>>> - But then basename() != name(), but (since no parent)
>>> get_parent_object()->name() '.' basename() != name()
>>> (The name can't be changed, since it is meant to stay valid until
>> the
>>> object is deleted?)
>>>
>>> This may affect sc_event naming as well.
>>>
>>>
>>> 6.16.1 sc_object Description (see get_parent_object above)
>>>
>>> "... objects of a class derived from sc_object may be deleted at any
>>> time. When such an sc_object is deleted, it ceases to be a child."
>>>
>>> If it has child objects itself (in case of a process), what happens
> to
>>
>>> their position in the hierarchy? And their names?
>>>
>>> I would even prefer to have a restriction that in case, the "parent"
>>> object shall not be deleted/invalidated until all children have been
>>> deleted. But this might break "early invalidating" implementations.
>>>
>>>
>>> [JA] We have already agreed that dynamic processes may be terminated
>> while
>>> they still have children, in which case a call to get_parent_object()
>> for
>>> any orphaned objects returns a null pointer. On the other hand,
>> insisting
>>> that parent process objects cannot be deleted while they have surviving
>
>>> children would be a clean solution.
>>>
>>> Opinions?
>>>
>>> John A
>>>
>>>
>>>
>>>
>>
>>
>
>

-- 
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 · http://offis.de/en/
Phone/Fax: +49-441-9722-420/282 · PGP: 0x9161A5C0 · Skype: phi.har
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