JMeter Compilable JSR223 Usage Precautions - variables

Question

Update - TL'DR:
When it comes to the compilable and cacheable JSR223 Elements, I've saw people using all sorts of tactics dancing around it. I had my doubts and I had my answers here, and found that most of tactics I saw are done wrong:
If your JSR223 scripts are full of args[0], args[1], args[2] everywhere, then that's the wrong choice of tactic, even it is the best practice of JMeter, it is not the best practice in the software engineering and easy-maintenance point of view.
Even if you assign args[n] to some meaningful-named variables, it is not the best practice in JMeter either, as there are much simpler and straightforward ways.
Similarly, if you are following the advices of "using vars.get("") to get variables" (then assign them to some meaningful-named variables), it is not the best practice in JMeter either, as there are much simpler and straightforward ways.
The advice of "Don't use ${} in JSR223 scripts" is more a myth than the truth, as all the ${} using examples in this question are just fine.
Also, the advices of breaking up expressions like "ValidAssetIds_${i+1}_g" with "+" into "ValidCatalogAssetIds_"+ (i+1) + "_g" is just another myth, and in most cases untruth, as illustrated in this question.
Now, as per JMeter's best practices for JSR223:
The reason JSR223 Elements is recommended for intensive load testing over Beanshell or Javascript, is because it implements the Compilable interface, as Groovy scripting engine implements Compilable.
And, it tells people to
ensure
to check (enable) the Cache compiled script if available property to ensure the script compilation is cached
the script does not use any variable using ${varName} as caching would take only first value of ${varName}. Instead use:
vars.get("varName"),
like:
Else, the other option is to pass them as Parameters to the script, like this:
Now, my question are,
What would happen if I use
def my_var = vars.get("MY_VARIABLE")
log.info("The value of my_var is ${my_var}")
in above example? Would log changes in each iteration when MY_VARIABLE changes?
Instead of above, I also tried to use
def my_var2 = __V(MY_VARIABLE)
def my_var3 = ${__V(MY_VARIABLE)}
but somehow I wasn't able to get the values of MY_VARIABLE. What I'm missing?
what if my ${varName} is dynamically defined, what would happen if I use ${varName} in such form? Like,
case 1:
for(def i = 0; i < validAssets.size(); i++) {
vars.put("ValidAssetIds_${i+1}_v","${i+1}")
}
case 2:
def varName = ${__time(/1000,)}
vars.put("MY_Log","abc${varName}")
Would each iteration have their own MY_Log values, or they all will be the same? I know I can guess my conclusion from observations, but the purpose of this question is to let me (or people) know the precautions when it comes to using JSR223 that we might not be aware of before. thanks.

Answer 1

All the "precautions" are described in the documentation
When using this feature, ensure your script code does not use JMeter variables or JMeter function calls directly in script code as caching would only cache first replacement. Instead use script parameters.
For example if you define a random string via User Parameters:
and try to refer it as ${randomString} in Groovy - it will be "random" only during the first iteration, on subsequent iterations the "first" value will be used:
Questions 1 and 3 are using Groovy's string interpolation feature, it's safe to use unless there is a clash with other JMeter Variables names
Question 2: you need to surround the __V() function with quotation marks otherwise the variable value is resolved but it's not defined in Groovy causing compilation error, you should see a message in jmeter.log file regarding it
def my_var2 = "${__V(MY_VARIABLE,)}"
Check out Apache Groovy: What Is Groovy Used For? article for more information on Groovy scripting in JMeter context.