Re: DECAda/VMS - calling GETJPI

[Mats.Weber@elca-matrix.ch (Mats Weber)]

In article <31B2AF74.668E@dial.eunet.ch>, Alan Paterson
<paterson@dial.eunet.ch> wrote:

>Here's one for the VMS gurus (I can't post it to comp.os.vms, 
>'cos there's a psychopath there who throws abuse at me):
>
>I want to examine all processes currently active. The system 
>service to do this is, of course, GetJPI (either in Starlet or 
>Lib). To perform wildcard process search, this procedure 
>expects to receive a value of -1 for the process_id parameter. 
>Unfortunately, in the "official" spec-files for these 
>procedures, this parameter has the type UNSIGNED_LONGWORD. Ada, 
>quite correctly, objects to this kind of thing :-)

The best way of doing this is by calling process_scan (in Starlet or lib).
I have once written a program that does all this and displays all kinds of
process info (much better than show system). If you want it, send me
e-mail and I'll give you the source.

>So, what I now do is the following:
>
>   PID  : UNSIGNED_LONGWORD;
>   PID0 : INTEGER;
>   for PID0 use at PID'address;

This is erroneous in Ada 83, and at least dangerous without a pragma
Volatile or something. You should prefer Unchecked_Conversion, which will
work when Standard.Integer becomes 64 bits.

>begin
>   PID0 := -1;
>   loop
>      GetJPI(..., Process_Id => PID, ...);
>
>This works, but I can't help but wonder if there isn't a more 
>elegant way to do it. Does anyone have experience with this?

Yes, there is:

   PID  : UNSIGNED_LONGWORD := -1;
begin
   PID := -1;
   loop
      GetJPI(..., Process_Id => PID, ...);

works because System.UNSIGNED_LONGWORD is -2**31 .. 2**31 - 1.