What is the maximum number of globals allowed in one global file?

Question

I remember there was a limit discussed in a LabVIEW class, but I can't remember it. But I know I exceeded the number on one project and VERY WEIRD things happened. Does anybody know this number?
Thanks Much

Answer 1

HI Tbob,
You are going to earn the title of Global Enthusiast if you keep this up
Race conditions are to Globals as Venerial deseas is to sex. If you want to avoid the former then abstain from the latter.
Yes you can use globals.
In fact, I ran a benchmark comparing how fast I can read a global booean vs the same coded as a LV2 global. The Global booean was 6 (or was it 16?) times as fast.
When answering Q's that use phrases like "strange things" we bring up the race condition and point users to LV2's.
Sure text based programmers learn how to handle global access in multi-threaded environments. These types of interaction are implemented by making the global a protected section that are protected using semaphores. This same approach can be used to protect LV globals. Just ensure all reads and writes of teh globals are only done after acquiring the semaphore that protects the global. If you did thisfor all accesses to the global you would not have race conditons with globals.
Unfortunately this is a lot of work because now you have to deal with creating acquiring releasing the semaphores and this has to be done for each value you need to protect from simultaneous access.
Now if there was an easier way well then....
BUT THERE IS!
It turns out that when a VI is not reentrant (like in a LV2) LV implements a scheme that prevents simultaneous execution of the VI. So by using a LV2 you pick-up the resource locking with ZERO EFFORT!
So being lazy, I use the method that is imune from race conditons from the very begining. That way when my customer asks "Can I manipulate the cal values from any of the machines on the network?" I can say "YES, that was functionality is supported by the design".
I could not say that if I implemented the cal via globals.
So that is why I push LV2's and and discorage globals.
Ben
Ben Rayner
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