What is the best method for transmitting objects/tagged records?

What is the best method for transmitting objects/tagged records?

[Shark8]

I've been stumped for a while trying to consider how to use Streams
and the Distributed Systems Annex (Annex E) together for a parser;
such that a [possibly] remote task can take a stream (parsing text to
tokens could be done on either the client or host-systems and that
division still suffers from this problem) and generate an object from
it.

I'd originally had something like this:
- Entry: Read String
- Entry: Write Object

But this doesn't work for a class-wide object. As the only way to get
an object from a task is via an out parameter (meaning we cannot use
it as an initialization to some class-wide variable); we cannot safely
over-write an existing object of some similar class because we may be
passing out an extended object (which can only be bigger) which would
stamp on the adjacent memory.

So, Dimitry kindly pointed me to the correct way of doing so:
- Entry: Read String
- Entry: Write Tag
- Entry: Write Object over a class-wide variable which had been
initialized to the correct type via the dispatching constructor.

But the package Ada.Tags is of the wrong type/level to be included in
a remote_types or remote_interface package, so I cannot use that
method.

How would you go about transmitting tagged records across partitions
(with the intent that these partitions should be easily separable for
distribution at a later date)?

OR Should I just rewrite my package-hierarchy keeping in mind the
Remote_interface/Remote_Types/etc pragma restrictions?

Further, I concede that perhaps this is the wrong area to try to self-
teach (distributed computing) so any pointers to tutorials for using
the DSA would be welcome.

Re: What is the best method for transmitting objects/tagged records?

[Jeffrey Carter]

On 06/06/2011 05:26 PM, Shark8 wrote:
>
> So, Dimitry kindly pointed me to the correct way of doing so:
> - Entry: Read String
> - Entry: Write Tag
> - Entry: Write Object over a class-wide variable which had been
> initialized to the correct type via the dispatching constructor.
>
> But the package Ada.Tags is of the wrong type/level to be included in
> a remote_types or remote_interface package, so I cannot use that
> method.

Possibly use the external tag for communication, converting to a tag at the 
destination?

-- 
Jeff Carter
"I fart in your general direction."
Monty Python & the Holy Grail
05

Re: What is the best method for transmitting objects/tagged records?

[Shark8]

On Jun 6, 8:11 pm, Jeffrey Carter <spam.jrcarter....@spam.not.acm.org>
wrote:
> On 06/06/2011 05:26 PM, Shark8 wrote:
>
>
>
> > So, Dimitry kindly pointed me to the correct way of doing so:
> > - Entry: Read String
> > - Entry: Write Tag
> > - Entry: Write Object over a class-wide variable which had been
> > initialized to the correct type via the dispatching constructor.
>
> > But the package Ada.Tags is of the wrong type/level to be included in
> > a remote_types or remote_interface package, so I cannot use that
> > method.
>
> Possibly use the external tag for communication, converting to a tag at the
> destination?
>
> --
> Jeff Carter
> "I fart in your general direction."
> Monty Python & the Holy Grail
> 05

Well, I can't even WITH Ada.Tags w/o breaking the rules for the DSA
package-pragmas...
and even if I could I'd be somewhat hesitant* because they're
implementation defined:
"(75)
    S'External_Tag

        S'External_Tag denotes an external string representation for
S'Tag; it is of the predefined type String. External_Tag may be
specified for a specific tagged type via an
attribute_definition_clause; the expression of such a clause shall be
static. The default external tag representation is implementation
defined. See 3.9.2 and 13.13.2."
Per http://www.univ-orleans.fr/mapmo/systeme/Recup/systeme/logiciels/GRASP_Documentation/ada95lrm/rm9x-13-03.html

* I had an application that did some working on external tags to check/
change the structure a bit; then one day I updated GNAT and, lo and
behold, everything there quit working because GNAT's external-tag
formatting had been changed.

Re: What is the best method for transmitting objects/tagged records?

[tmoran]

I think I missed something.  Are you trying to implement the
marshalling/unmarshalling part of a Partition Communication Subsystem?

Re: What is the best method for transmitting objects/tagged records?

[Randy Brukardt]

"Shark8" <onewingedshark@gmail.com> wrote in message 
news:5e5bc0bb-8b39-4655-8c9d-f93ec24b3529@p21g2000yqh.googlegroups.com...
>...
>"(75)
>    S'External_Tag
>
>        S'External_Tag denotes an external string representation for
>S'Tag; it is of the predefined type String. External_Tag may be
>specified for a specific tagged type via an
>attribute_definition_clause; the expression of such a clause shall be
>static. The default external tag representation is implementation
>defined. See 3.9.2 and 13.13.2."
>Per 
>http://www.univ-orleans.fr/mapmo/systeme/Recup/systeme/logiciels/GRASP_Documentation/ada95lrm/rm9x-13-03.html
>
>* I had an application that did some working on external tags to check/
>change the structure a bit; then one day I updated GNAT and, lo and
>behold, everything there quit working because GNAT's external-tag
>formatting had been changed.

If you are depending on the format of the external tags, you surely should 
not be depending on the default values for external tag for those particular 
tags. But you can specify these youself, and if you do that compiler won't 
change them. Note that the text you quote says that 'External_Tag can be 
specified.

This is exactly how you stream tagged values -- there too it is a bad idea 
to depend on the default external tags unless everything will always use the 
same compiler version everywhere. Specifying the tags is better.

                                          Randy.

Re: What is the best method for transmitting objects/tagged records?

[Shark8]

On Jun 6, 9:53 pm, tmo...@acm.org wrote:
> I think I missed something.  Are you trying to implement the
> marshalling/unmarshalling part of a Partition Communication Subsystem?

I think that's what it amounts to, yes.
(Though I don't think I realized it until you put it in those terms.)

Re: What is the best method for transmitting objects/tagged records?

[Shark8]

On Jun 6, 10:25 pm, "Randy Brukardt" <ra...@rrsoftware.com> wrote:
> "Shark8" <onewingedsh...@gmail.com> wrote in message
>
> news:5e5bc0bb-8b39-4655-8c9d-f93ec24b3529@p21g2000yqh.googlegroups.com...
>
>
>
>
>
>
>
>
>
> >...
> >"(75)
> >    S'External_Tag
>
> >        S'External_Tag denotes an external string representation for
> >S'Tag; it is of the predefined type String. External_Tag may be
> >specified for a specific tagged type via an
> >attribute_definition_clause; the expression of such a clause shall be
> >static. The default external tag representation is implementation
> >defined. See 3.9.2 and 13.13.2."
> >Per
> >http://www.univ-orleans.fr/mapmo/systeme/Recup/systeme/logiciels/GRAS...
>
> >* I had an application that did some working on external tags to check/
> >change the structure a bit; then one day I updated GNAT and, lo and
> >behold, everything there quit working because GNAT's external-tag
> >formatting had been changed.
>
> If you are depending on the format of the external tags, you surely should
> not be depending on the default values for external tag for those particular
> tags. But you can specify these youself, and if you do that compiler won't
> change them. Note that the text you quote says that 'External_Tag can be
> specified.
>
> This is exactly how you stream tagged values -- there too it is a bad idea
> to depend on the default external tags unless everything will always use the
> same compiler version everywhere. Specifying the tags is better.
>
>                                           Randy.

Good idea. Thank you.

Re: What is the best method for transmitting objects/tagged records?

[tmoran]

>> marshalling/unmarshalling part of a Partition Communication Subsystem?
>
>I think that's what it amounts to, yes.

  Sending an object over a comm link differs from writing to/reading from
disk only in timing.  In CLAW, the different kinds of bitmaps (8 bit pixel,
24 bit, etc) are children of a root type.  The Write routine for each
child writes a standard .bmp file.  The Read routine is

  function Read (Filename : in String)
    return Claw.Bitmaps.Root_DIBitmap_Type'class;

It reads the header of the bmp file then does
        if Header.Private_Info.Color_Depth = Claw.Bitmaps.VGA and
           Header.Private_Info.Compression = Claw.Bitmaps.BI_RGB then
            declare
                Result : Claw.Bitmaps.VGA_DIBitmap_Type( height, width);
            ... read data into VGA_DIBitmap_Type data structure
                return Root_DIBitmap_Type'class(Result);
            end;
        elsif Header.Private_Info.Color_Depth = Claw.Bitmaps.EGA ...

Re: What is the best method for transmitting objects/tagged records?

[Shark8]

On Jun 7, 1:06 pm, tmo...@acm.org wrote:
> >> marshalling/unmarshalling part of a Partition Communication Subsystem?
>
> >I think that's what it amounts to, yes.
>
>   Sending an object over a comm link differs from writing to/reading from
> disk only in timing.

Which is exactly why using tags and streams is a good idea.
The main problem is that the package that defines the tag-type is not
WITH-able by packages that are Remote_Types / Remote_Interfaces.

So, even a function that has a parameter-footprint of
"Procedure ( Tag : In Out Ada.Tags.Tag )" is invalid

(WITH-ing Ada.Streams is fine because it is a Pure package.)

Re: What is the best method for transmitting objects/tagged records?

[Randy Brukardt]

"Shark8" <onewingedshark@gmail.com> wrote in message 
news:fb72e599-968f-4850-abf7-1ed1fc8e50c3@d1g2000yqm.googlegroups.com...
On Jun 7, 1:06 pm, tmo...@acm.org wrote:
>> >> marshalling/unmarshalling part of a Partition Communication Subsystem?
>>
>> >I think that's what it amounts to, yes.
>>
>> Sending an object over a comm link differs from writing to/reading from
>> disk only in timing.
>
>Which is exactly why using tags and streams is a good idea.
>The main problem is that the package that defines the tag-type is not
>WITH-able by packages that are Remote_Types / Remote_Interfaces.
>
>So, even a function that has a parameter-footprint of
>"Procedure ( Tag : In Out Ada.Tags.Tag )" is invalid
>
>(WITH-ing Ada.Streams is fine because it is a Pure package.)

Right, but you don't need to use Ada.Tags (or anything tags) in order to 
stream tagged types. Just use the provided T'Class'Input and T'Class'Output 
attributes. For those to have portable results, you need to specify your 
external tag values for your tagged types (we previously discussed that).

                                            Randy.

Re: What is the best method for transmitting objects/tagged records?

[Shark8]

On Jun 8, 7:49 pm, "Randy Brukardt" <ra...@rrsoftware.com> wrote:
> "Shark8" <onewingedsh...@gmail.com> wrote in message
>
>
> >(WITH-ing Ada.Streams is fine because it is a Pure package.)
>
> Right, but you don't need to use Ada.Tags (or anything tags) in order to
> stream tagged types. Just use the provided T'Class'Input and T'Class'Output
> attributes. For those to have portable results, you need to specify your
> external tag values for your tagged types (we previously discussed that).
>
>                                             Randy.

Oh!
{ I assume you mean something like Function Parse( Input :
stream_type ) Return Hierarchy_Parent'Class; no? }

So I was right in that I need to redefine my interfaces.

I currently have a task; which cannot return values as a function
would, and therefore cannot be used to
directly initialize an class-wide variable.

What I'm going to have to do then, is 'hide' the task in the body;
something like this:
Package Parser is

Task Type Parser_Task is
 -- Get Text and get_Token do essentially the same thing; in my setup
 -- I would like to try the tokenizing on client- and server-side
 -- to compare the efficiencies of the two.
 --
 -- Sorry about the poor naming & invalid code; I'm just typing up
psudeocode.
 Entry Get_Token(Token_Stream : Access stream); -- reads a token
 Entry Get_Text( Text_Stream : access stream ); -- read text-stream
 Entry Get_Tag(  The_Tag : Out Tag  );
 Entry Get_Object( The_Object : Out Object'Class );
End Parser_Task;

[...]
The_Parser : Parser_Task;
[...]

Function Pars( Input : Access Ada.Streams.Stream'Class ) Return
Object'Class is
 T : Tag;
begin

The_Parser.Get_Text( Input );
The_Parser.Get_Tag( T );

-- use dispatching construction
Declare
 This_Object : Object'Class:= Dispatch( T );
Begin
 The_Parser.Get_Object( This_Object );
 Return This_Object;
End;

end Parse;

End parser;

Re: What is the best method for transmitting objects/tagged records?

[Simon Wright]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> Right, but you don't need to use Ada.Tags (or anything tags) in order
> to stream tagged types. Just use the provided T'Class'Input and
> T'Class'Output attributes. For those to have portable results, you
> need to specify your external tag values for your tagged types (we
> previously discussed that).

Not sure what you mean by 'portable' here, Randy; are compilers required
to conform to standard representations on the wire? Because GNAT
certainly doesn't out of the box (for example, it uses native byte
order).

Re: What is the best method for transmitting objects/tagged records?

[Randy Brukardt]

"Simon Wright" <simon@pushface.org> wrote in message 
news:m2sjrj4mpe.fsf@pushface.org...
> "Randy Brukardt" <randy@rrsoftware.com> writes:
>
>> Right, but you don't need to use Ada.Tags (or anything tags) in order
>> to stream tagged types. Just use the provided T'Class'Input and
>> T'Class'Output attributes. For those to have portable results, you
>> need to specify your external tag values for your tagged types (we
>> previously discussed that).
>
> Not sure what you mean by 'portable' here, Randy; are compilers required
> to conform to standard representations on the wire? Because GNAT
> certainly doesn't out of the box (for example, it uses native byte
> order).

Good point; the byte order could change. As a matter of course, I would only 
put things (records) on the wire that already had representation clauses 
fully specifying their layout (and that includes external tag). In that 
case, your results will continue to work until/unless you have to change 
processors (the native byte order surely doesn't change).

Ada doesn't out of the box support any sort of hetrogeneous partitioning 
(the assumption is that all of the processors are similar) and if your 
implementation provides some it is doing so outside of Ada. (That is, if you 
have partitions with different native byte orders communicating, you are 
trying to do something Ada was not designed for.)

                                           Randy.

Re: What is the best method for transmitting objects/tagged records?

[Randy Brukardt]

I said:
...
> Ada doesn't out of the box support any sort of hetrogeneous partitioning 
> (the assumption is that all of the processors are similar) and if your 
> implementation provides some it is doing so outside of Ada. (That is, if 
> you have partitions with different native byte orders communicating, you 
> are trying to do something Ada was not designed for.)

Clarification: I'm talking about Annex E distributed system partitions here, 
and not just stream communication between the partitions, in line with the 
OP's original question.

                                  Randy.

Re: What is the best method for transmitting objects/tagged records?

[tmoran]

>> Ada doesn't out of the box support any sort of hetrogeneous partitioning
>Clarification: I'm talking about Annex E distributed system partitions here,
  A (slow) PCS could consist of a flash drive carried between machines.
You wouldn't expect a binary dump of a Windows Ada pixel array to be directly
readable as such on a DVD player.  Ditto if the PCS uses fast ethernet.
You need to write your own 'Input/'Output to intercovert with some common data
format.

Re: What is the best method for transmitting objects/tagged records?

[Simon Wright]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> Ada doesn't out of the box support any sort of hetrogeneous
> partitioning (the assumption is that all of the processors are
> similar) and if your implementation provides some it is doing so
> outside of Ada. (That is, if you have partitions with different native
> byte orders communicating, you are trying to do something Ada was not
> designed for.)

Looking at
http://www.adaic.org/resources/add_content/standards/05aarm/html/AA-E.html,
(6) leaves it up to the implementation whether the distributed system
must be homogeneous.

However, (7) [Note 1] requires the impementation to support
configuration changes without recompilation, which strikes me (as an
interested bystander) as a very demanding requirement and one I would
have thought potential users would be able--if reluctantly--to do
without.

Are Notes normative?

Re: What is the best method for transmitting objects/tagged records?

[AdaMagica]

> Are Notes normative?

No, see RM 1.1.2(14..16)

Re: What is the best method for transmitting objects/tagged records?

[Robert A Duff]

Simon Wright <simon@pushface.org> writes:

> Are Notes normative?

No, but they are true.  That is, they follow from the normative rules.

- Bob

Re: What is the best method for transmitting objects/tagged records?

[Simon Wright]

Robert A Duff <bobduff@shell01.TheWorld.com> writes:

> Simon Wright <simon@pushface.org> writes:
>
>> Are Notes normative?
>
> No, but they are true.  That is, they follow from the normative rules.

Ah, I'd forgotten how to speak Requirements. So when Note 1 says "The
partitions comprising a program *may* be executed on differently
configured distributed systems or on a non-distributed system without
requiring recompilation." [my emphasis] there's no requirement on an
implementation to actually do this.

Re: What is the best method for transmitting objects/tagged records?

[Robert A Duff]

Simon Wright <simon@pushface.org> writes:

> Robert A Duff <bobduff@shell01.TheWorld.com> writes:
>
>> Simon Wright <simon@pushface.org> writes:
>>
>>> Are Notes normative?
>>
>> No, but they are true.  That is, they follow from the normative rules.
>
> Ah, I'd forgotten how to speak Requirements. So when Note 1 says "The
> partitions comprising a program *may* be executed on differently
> configured distributed systems or on a non-distributed system without
> requiring recompilation." [my emphasis] there's no requirement on an
> implementation to actually do this.

That's the other thing about notes -- they're often written
sloppily (it's not clear whether the programmer may do that,
or the implementation may).

I believe the implementation is required to support that.

- Bob

Re: What is the best method for transmitting objects/tagged records?

[Marco]

On Thursday, June 9, 2011 4:42:55 PM UTC-7, tmo...@acm.org wrote:
> >> Ada doesn't out of the box support any sort of hetrogeneous partitioning
> >Clarification: I'm talking about Annex E distributed system partitions here,
>   A (slow) PCS could consist of a flash drive carried between machines.

  Ah sneaker-net lives on :)