Semaphore GOOP Help

Question

My Quandry:
I am dynamically launching multiple VIs, but I am interested in them sharing a single resource (say, data stored in a GOOP-style/Old-style global.). So I want to use a semaphore to coordinate which VI has access to the resource.
I have a VI that calls the object VI, which creates the semaphore and stores it in its shift register. Then I dynamically launch the resource(s) that use the object VI.
What I find is that the semaphore becomes invalid the minute that the top-level VI (which set everything up) is done.
This makes no sense to me, as the refnum is stored in a shift register in a subVI that is contained by an executing VI.
It is also causing me a big problem in my application.
Who can explain this?
SEE EXAMPLE.
Note: the example was written in 7.1, but also evidences the behavior in 8.0
Attachments:
DEBUGSemaphore.llb ‏85 KB

Answer 1

Lets see if I can add some value without getting stuck!
There is a size input fo rthe create semaphore.
That determines how many enities can get the semaphore.
When a semaphore is requested and obtained, that value gets decremented. When the value is zero, nobody else get the semaphore. When the semaphore is released tha value is incremented.
This how LV tracks if the semhpre is in use.
When a VI evaluated to determine if it can be unloaded the resource taht were allocated by that VI are checked to see if they are in use. That is done by looking a the semaphore count and the max size.
So...
1) When the semaphore is created set the size = 2
2) Imediately after creating it, acquire the semaphore. (that should leave one for everyone else).
3) Everything else codes the same until the end.
4) At shutdown time, the entity that will destroy the semaphore should do a "release" prior to the destruction.
I have not tested this but this is how I understand it and what I would try if I was faced with this challenge.
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction