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Paula LG avatar image
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Paula LG asked Sam Stubbs commented

A*Navigator stuck on calculating path

Hi,

I've recently noticed an unusual behavior while developing some models.

I have a certain amount of task executers (defined by a Delete and Copy Group Members parameter). When the simulation starts, I create a dummy transporter for each task executer and make them travel between 2 stations in a loop. These dummy transporters are added to a group called "Dummies", and every object that belongs to that group is destroyed On Model Reset.

There's a moment during the simulation where the model gets stuck. If we then start recording with the performance profiler, we can see that the A*Navigator is stuck trying to calculate a path. No error pops up, it just can't run any further.

I have developed a dummy model to replicate the issue I encountered: 24.1 Dummy AStarNavigator stuck.fsm

We have also tried to run it in 24.2 Beta and the exact same thing happened.

Thank you in advance!

FlexSim 24.1.1
bug reportastar navigator
241-dummy-astarnavigator-stuck.fsm (42.9 KiB)
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2 Answers

Sam Stubbs avatar image
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Sam Stubbs answered Sam Stubbs commented

Deadlock management is a tricky issue to resolve in AStar. The problem is that you have groups of taskexecuters running between two locations back and forth in a straight line, and they are all crowding at those two locations. With that much overlapping traffic, and collision detection, it's no wonder there is deadlocking going on.

My recommendation is to use preferred paths to create in and out drop off and pick up routes around your queues (like you'd probably use in real life). It also helps to add your locations to the AStar navigator as well. Create a flow that helps space out and direct your travelers so they aren't all overlapping with each other.

Here's a version of your model using the preferred path method.

241-dummy-astarnavigator-stuck_2.fsm


241-dummy-astarnavigator-stuck-2.fsm (48.0 KiB)
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Paula LG avatar image Paula LG commented ·

Hi Sam,

Thank you for taking the time to explore the issue I presented on this post. The routing I had on the original model was more complex than a simple straight line between two stations; however, it is true that a lot of transporters had to follow the same route. When I first noticed it happened, I tried using preferred paths as you just suggested, but it kept happening. If I run the model you attached for a long time, I get a deadlock error that FlexSim is able to identify, as opposed to what I initially reported.

I understand that this kind of crowded routing can easily lead to traffic problems, but I reported it as a bug because FlexSim doesn't detect it as an error, no message window pops up and no error is registered on the console.

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Sam Stubbs avatar image Sam Stubbs ♦ Paula LG commented ·

Yeah the behavior of getting stuck without reporting a deadlock does seem like an unintended response (or lack of response) from FlexSim.

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Jason Lightfoot avatar image
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Jason Lightfoot answered Paula LG commented

I would try adding a deallocation time offset (e.g. 0.5 secs) which seems to resolve the issue.

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Paula LG avatar image Paula LG commented ·
Hi Jason,
Thank you for your answer! I already tried what you recommended, but it only delayed the issue; the model still got stuck at a larger simulation time.
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