Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!pasteur!ucbvax!carleton.EDU!BARMSTRO
From: BARMSTRO@carleton.EDU (Pod Stolom Consulting)
Newsgroups: comp.os.vms
Subject: RE: question on chaining images
Message-ID: <8803201558.AA10998@ucbvax.Berkeley.EDU>
Date: 15 Mar 88 01:44:00 GMT
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 40


        Mary Malmos asks about chaining images such that the original
        image will be resumed after the second image terminates, and
        will be resumed at the point where the second image was called,
        all using a single process.

My understanding of VMS process control is that there is no way to do this, at
least not one that already exists. You would need to copy the whole process
header (or most of it) to memory somewhere in physical memory before doing the
image initialization for the second program and then have some way of copying
this information back into the process header after the image rundown for the
second program, much like pushing and poping stack frames before and after
procedure calls.  The process header would have to be stored in physical memory
because the real memory for the first image would be wiped clean when the
second program initializes.  Since the rundown of the second image would again
cause real memory to be wiped clean, you would have to write a _third_ program
to move the physical copy of the process header back into memory, including all
the pages in the working set, and run the first and third program in a command
procedure. Access to the process header is ugly, and may not suffice to
recreate the status of the original image.  Furthermore, the format of the
process header will inevitable change with VMS 5.x. 

This is all assuming that you are running compiled images.  An interpreted
environment would behave quite differently. 

There have been many occassions when I would have found this ability very
useful.  If I overlooked something in my own searches, I would be delighted to
hear about it.  I shan't be holding my breath, however. 

Disclaimer:  I may not have the _vaguest_ idea of what I am talking about.


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| Borden Armstrong                               Computer Center        |
| System Manager and                             Carleton College       |
| Academic Programmer/Analyst                    1 North College Street |
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| barmstro@carleton.edu                                     U. S. A.    |
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