In a separate e-mail, a friend wrote, "Also, a long time ago in one of the
e-mail exchanges, you labeled the display manager variable method of
invoking a program on the AP from a sequence block as a "kludge". Fritz
gave testimonials to the usefulness of your CP-Shell utility, but you never
explained the pitfalls of the DM variable method and it certainly seems to
be used by a lot of people."
So, I thought I'd address this omission. Hope you folks don't mind.
The major difference between using a command server like cpShell and
the DMCMD variable is that if the DM variable does not exist you will get an
error in your script that you must have an SBX to handle. SBX code is
somewhat complicated - as are all such exception handlers in any language.
One of the major difficulties is writing the SBX code is that you
probably want different actions based on different places in the code and
that is relatively hard to do in a systematic manner. While one could use
the appropriate parameter of the block to get the statement number of the
error, the code has to be adjusted each time lines are added or deleted.
This is a major hassle.
cpShell and other message servers allow the use to use 'SENDCONF' to
send a message to it. SENDCONF has a time out check and it sets the SUSPND
bit. The program/script run by cpShell can reset the SUSPND bit to indicate
that the action is complete. Errors are handled by timeout code which is
easier to write than SBX code.
Regards,
Alex Johnson
The Foxboro Company
10707 Haddington
Houston, TX 77043
713.722.2859 (v)
713.722.2700 (sb)
713.932.0222 (f)
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
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