Java concurrent queue for tag change scripts

[pturmel]

Did you read the linked topic in the first post?

Some more about this:

Best practices and pitfalls with Tag Event Scrips

In summary, my question is: What is best practices, and what to avoid when writing Tag Event Scripts? Background and more details regarding question: From what I have read, the Tag Event Scripts are running in fixed size thread pool (default 3 threads). This would mean that if you have multiple Tag Event Scripts that does slow/blocking operations, it could block any other tag event scripts from running. This would presumably mean that running e.g. network calls like OPC calls, or other poten…

system.util.invokeAsynchronous() is a very heavy-weight tool and should not be used where you could make hundreds or thousands of threads.

[louagejasper]

Oh, I looked over that link in the first post. That clarifies the use case allot, thanks!

[nminchin]

@pturmel

Ok. Updated in place: queueUtil.py

Hey @pturmel, how does this work with redundant gateways? What will happen to enqueued items if the redundant gateway kicks in? I assume these are dropped if the GW goes down. How would you make it more tolerant?

[pturmel]

Dropped on failover.

You will need a bunch of state management in your queue draining routine to detect when it is newly "live" after fail-over, and run discovery/recovery code.

Ignition redundancy isn't really designed for seamless state hand-off in any case.

[louagejasper]

Another question that comes to mind:

In an expression tag, is using runScript on a timer subject to the same vulnerability? Or is that an entirely different system in Ignition?

[pturmel]

@louagejasper

subject to the same vulnerability?

Yes, it is a separate thread pool for expressions, but is also size three. Scripts won't block expressions and vice versa, but long-running expressions can block all tag expression execution.

[nicholas.gutt]

I have been trying to get queueUtil to work, failing hard....

I am confused maybe someone, pturmel, or nminchin explain:

what exactly goes into the tagChange script?
what exactly goes into the Gateway Event Timer script?

[pturmel]

Did you read the multiline comment string between the copyright and the imports? Examples right there.

Let me summarize:

• In those examples, replace "ABC" with some reasonable name for what you are doing.

• Place queueUtil.py into a library script named queueUtil in an inheritable project that will be included in both your gateway scripting project and whatever project will run the timer events.

• In the gateway scripting project, create a library script to contain the assignment to processABCqueue and the function definition enqueueABC.

• In every tag (or UDT) that need to run this process. make a value change event with the one-liner someScriptGSP.enqueueABC(...) as described in the comment above that example.

• In the background events project, create a library script to contain the assignment to processABCqueue and the function definition processABC, including the decorator.

• In one or more (if workload justifies) timer events in the background project, make one-liner calls to someScriptBG.processABC(). (No arguments.)

Also, make sure my Integration Toolkit is installed.

[nicholas.gutt]

I have the Integration Toolkit installed.

I put queueUtil in my gateway scripting project, currently gateway inheritance is a single project. Not a structure like your docstring calls out.

processABCqueue and the function definition enqueueABC.
I did not understand needed to be in a separate library project.

I unfortunately will not be able to do anymore ignition work until next week, going on vacation.

Ill report back when I am successful.

Thank you! Your advice is very valuable.

[pturmel]

Ok, Can be one script in a single project. The docstring calls out the requirements based on split duties for different kinds of projects.

[nicholas.gutt]

@pturmel

In the background events project, create a library script to contain the assignment to processABCqueue and the function definition processABC, including the decorator.

I got queueUtil working! Thank you again for providing the community with your time, software, and expertise. I have solved many problems using your advice.