Re: For the AdaOS folks

["Warren W. Gay VE3WWG" <ve3wwg@NoSpam.cogeco.ca>]

Dmitry A. Kazakov wrote:

> On Sun, 02 Jan 2005 17:04:29 -0500, Warren W. Gay VE3WWG wrote:
>>Dmitry A. Kazakov wrote:
>>>On Sat, 01 Jan 2005 19:31:56 -0500, Warren W. Gay VE3WWG wrote:
>>And how do your identify your GNAT object? At the end of the day,
>>you still have to grapple with "names" and "identities". Only
>>the details change.
> 
> The "detail" is that you identify not some GNAT installation file #1534,
> but GNAT. GNAT itself is easy to find, 

Is it? What if you 2 or 3 versions of it?  There is an interesting
situation now with windows as well, since you can have a cygwin
version in addition to the usual gnat-3.15p type of release.

> its components are not. They may
> vary from version to version. It is GNAT's responsibility to know them, not
> of GNAT user.

If I want to install a binding, I need to know where GNAT has installed
its bindings (like win32). The registry makes this a trivial thing to
do (I know, because I have used it).

>>So just how do you expect to identify what piece of software
>>you want to know about, without using a name (or identity if
>>you prefer)? OO doesn't do away with this requirement.
> 
> ADT allows to organize it in a proper way. We are using types to forget
> about bytes. In OSes we are still using "bytes" = files.

You haven't answered how you are going to identify your
object. This doesn't explain it away.

>>Can native objects be exported from operating systems? A
>>quick survey produces this list:
>>
>>   - integer file descriptor (POSIX)
>>   - handles (Windows)
>>   - ports (Mach)
>>   - identities (L4)
>>   - ipc ID (UNIX SysV) for message queues, shared mem etc.
>>
>>These are all fancy "handles" of one sort or another. You won't
>>get much more than that from any O/S. Why? How do you share an
>>object in protected-mode with a user-mode process? You can't.
>>Even if you could, there would be parts of objects that the
>>O/S wouldn't want you to mess with, or perhaps even look at.
>>Maybe you can't because the object is just a Mach port.
>>
>>The best API answer seems to be to just provide a handle that
>>can be used to refer to the object (like an Ada access type),
>>or in the case of a Mach port, be the object metaphore. Then
>>you call varied API set (effectively methods) on that object,
>>using the given handle(s).
> 
> It is not like Ada access type, because handle is not a pointer. 

I am not suggesting they are the same, but merely that they are
used for the same purpose.

> It is a
> key in some associative array. To "dereference" it you have to switch to
> supervisor mode. Then you have to check it, because somebody could mess
> with its value etc. It is very inefficient. You have to do all this even if
> you call a function of a protected object, which could be safely performed
> in user-mode. BTW, the very notion of user-mode is also of old procedural
> fashion. A protected object is passive. You should be able to access it in
> any "mode". But when you want to queue to its entry or to call its
> procedure, only then you have to switch the context to make the object data
> available to write. It is not kernel business anymore.

But if you were to replace the file descriptor with an object that
implements the equivalent of a v-node, you wouldn't be able to do
this in "user mode".

> Your RPC services is another model. They are monitors. These can be exposed
> in API as tasks to have rendezvous with. 

Or they could be simple procedure/function calls in Ada. It is merely
a point of presentation.

> Again OO/ADT could bring great
> advantages here. Imagine extensible tasks. Presently, if you have some
> sequence of actions to be performed on one service, you have to care about
> locking, serializing, then you implement it as separate inefficient RPCs to
> the server. Service extensions would be sort of stored procedures in DB
> terms.

Again, you can package it any way you like already. Just wrap it
in the trimmings you want.

>>Then if you want it to look different than that, you provide
>>a binding. The general idea however, is that an Ada based
>>O/S will have native bindings. The packages won't be
>>adaptations of C header files etc.
> 
> OK, but that is more like C programming in Ada to me. 

Why?

> This new OS will not
> become a breakthrough. It will be a stable decent OS, but who needs that?

Firewalls for one.

> See what happened with VMS? The only way to kill the Windows/UNIX monster
> to offer something really revolutionary.

I am not on any quest for world domination, though I don't
discourage others from trying to do so ;-)
--
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg