I have a complex program that uses a times loop to call other program. I have reduced the problem to a simplified example. The calling program has two examples: Selecting the broken example shows how the program hangs. Selecting (not selecting broken) shows how the program emulates a times loop and calls the underlaying VI successfully. When successful, the counter on the main program increments. When hung, nothing happens. The program called does two things: It initializes as event structure inside a while loop, waits for the initialization, calls the event structure with a trigger, which exits the while loop and returns to the main program. I should emphasize again that this simple program is to illustrate the bug (or my lack of understanding of timed structures). The real program is more complex but shows the same behavior. Then called from the main program with the timed loop, the flag is never set and the other parallel tread waits causing the hang. This only happens with a timed loop as the calling entity as the other instance works fine as well as running the VI alone. You can fix this version by placing the flag outside of the timeout event structure. This will fix this bug BUT in a more complex program, that fix fails. I also included the fixed version for a comparison. For some reason, the timed loop never initializes the called event structure. It is as if the timed loop priority takes precedence over the called program (I tried modifying that value but more bugs occurred). Any ideas? I emulated the timed loop in similar ways to the working case (false case in calling program - yes I should have named them working and broken rather than true and false) and can go on with the larger program but I would like to understand this bug as it may illustrate my lack of understanding of timed loops or something for NI to explore. I am using LV19.1. .

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LabVIEW

Time loops problem

Solved!

@dkidw2010 wrote:

We now agree that this is a problem in LV and not the logic of the programmer (me). I will mark this tread as complete.

Apparently, the timed loop does just generate one tread for execution, as I guessed. I do not agree that this is important aspect of timed loops as one could use them for polling. In any case, nothing is mentioned in the documentation nor restrictions on their use.

I have attached another example of why it fails (and could likely think of many more). This example is just using two dependent loops. Apparently, any process that waits on another will cause it to fail whereas it works fine when called from a typical while loop.

Thanks for you help. I learn something new everyday.

I disagree. This is like using a screwdriver as a hammer and then complaining that it doesn't drive nails into wood and then blaming the screwdriver for not working correctly.

Bill

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