I am going to create a script that will use many consecutive loops waiting on a tag changes to progress. How can I tell if a script is stuck waiting for the tag change event to exit the loop? I do plan on haveing a timeout feature but as I develop the script I expect to have failures so want to be prepared for finding and stopping endless loops.
pseudo code would be:
Set transaction group handshake tag to zero
Trigger transaction group
Loop while transaction group handshake tag = zero .
Set transaction group handshake tag to zero
Trigger transaction group
Loop while transaction group handshake tag = zero .
Set transaction group handshake tag to zero
Trigger transaction group
Loop while transaction group handshake tag = zero .
This is an extremely dangerous script design in Ignition. Don't do any kind of busy-wait or sleep-wait in any Ignition event script. Full stop.
Instead, create a state machine, using either a memory tag, or, more robustly, a top-level project script collection object (typically a dictionary). Use gateway tag change events and gateway timer events to drive forward progress. Use a threading.RLock object instance to protect against simultaneous changes from different threads.
SFC has been reliable where I've used them. OTOH, I don't use them outside of a gateway scope either. I seem to notice that when people try to use them to interact with a client that things go pear shaped. Just my observation. That and a couple bucks will buy you a soda.
