Re: How to determine if program is running in QSHELL

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 01/10/2009, at 10:51 AM, CRPence wrote:

>   FWiW [although you already know this :-)]: The search for the
> program could be made easier by using [i.e. deferring to the logic
> in] the QMHSNDPM API instead,

Just finalising this thread.

Yes, I did know that :) but dropped it from my consideration for the  
same reason as I dropped materialising the call stack. Message  
handling is a very useful and powerful function but it's also quite  
slow. I did not have empirical data to support that--just experience  
and "gut feel".

So to close things off properly I wrote three trivial test programs  
this morning just to see the timing differences. One uses my original  
getppid() idea, one uses Dave McKenzie's call stack suggestion, and  
the final one uses Chuck Pence's send message suggestion.

I ran the code from within QSHELL via symbolic links. I ran each test  
multiple times and took the best time. Here are the test results from  
a model 170-2291 running VRM510.

time_getppid	632 microseconds

time_sndpmsg	1624 microseconds

time_callstk	13312 microseconds

If anyone wants to see the test code just let me know.

The call stack test could be sped up by declaring sufficient storage  
for 5 entries and only do a single call to retrieve just that many  
entries "knowing" the desired entry is probably the 3rd one in the  
stack but it still wouldn't be as fast as the getppid() version.

Given that the point of this code was to determine whether a program  
is running in QSHELL and that is likely to be invoked only once on any  
given call then any of these methods would suffice. The getppid()  
method was less lines of code and faster so I'm happy that's the one I  
implemented. My "gut" was right--so pleased it can do more than make  
noises and bad smells.

Regards,
Simon Coulter.
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