Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Tue, 28 Jun 2005 15:52:49 +0200

Kay-Uwe Kasemir wrote:

Yes, Jeff proposes a channel::createAllPropertiesReadRequest.
Does that cover your idea for a simply 'probe'- type application?

     createAllPropertiesReadRequest
     ...
     foreach p ( da->getProperties() )
     {
         display da->getType(p), da->getAsString(p)
     }

... or would you also like to see a request that only
gets the properties and types, without fetching any actual values?

Yes, we need that request!

(And I think we already agreed on it at the SLAC meeting, but everyone

seems to have different memories of that meeting to an extent that I

start to believe we attended different parallel meetings. Or the same

meeting in parallel worlds.)

Let me give two reasons why:

1. Access Rights
The Viewer (read) traverse() will only show properties that are readable.

The Manipulator (write) traverse() will only show properties that are

writable.

Both could be limited down to very few by Access Security or a similar

mechanism.

If a probe-type client wants to show all properties and the access

rights for each of them, there has to be another traverse() that shows

*all* properties, together with the access rights for each.

2. Primitive Types

Data Access hides the native type of the data by providing templated

functions for each of the interface types that do all necessary

conversions. The only way for a client to find out about the native type

of data is to provide a bunch of Viewers (one for each interface type)

and see which one gets called. (If for a particular non-C++ dataAccess

implementation the interface type is different from the internal

primitive type, even this method will only get a hint.)

So the third traverse() should also yield the native primitive type for

a property (one out of a list of well-known, machine, architecture,

language independent and size-fixed primitive types).

Ralph

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System