Somtime issues when Read csv data config from jmeter

Question

I have an issue when creating a performance script, which has related to reading data from csv data config.

My script has a structure below:

• setup Thread
• Create csv Thread. After view dashboard, using Json extractor to get list of data and put it to csv file

Create csv file - After this thread, i will have a lot of csv file base on number of center. For example: 4 files with different names

String[] attempt = (vars.get("ListAttemptId_ALL")).split(",");
int length = attempt.length;
String dir = props.get("UserFilePath").toString();
String center = vars.get("Center");

File csvFile = new File(dir, center + ".csv");

if(!csvFile.exists()){
    FileWriter fstream = new FileWriter(csvFile);
    BufferedWriter out = new BufferedWriter(fstream);

    for(int i = 1; i <= length; i++){
            out.write(attempt[i-1]);
            out.write(System.getProperty("line.separator"));
    }
    out.close();
    fstream.close();
}

Next thread gets the name of the file and using CSV file to loop over all line

String center = vars.get("Center"); 
String fileName = center + ".csv";
props.put("path_${__threadNum}", String.valueOf(fileName));

Because i have alot of threads will run the same file, so i just check __threadNum of to find the name of the file this thread need to use. I'm using loop Controller to go over CSV file, run to the end of the file will stop thread. Here is inside this loop

CSV data Set config:  
Filename: ${__property(UserFilePath)}\\${__P(path_${__threadNum})}  

where ${__property(UserFilePath)} = path of the folder and ${__P(path_${__threadNum})} is name of the csv file were extracted

My issue is this code is not stable, sometimes threads can read file normally, sometimes it's show error that file does not exist (actually it did) so it's hard to chase that where issue from. Can anyone suggest a solution to my issue? Or suggest any idea better than my solution to read csv file in thread group?

Answer 1

I have answer for this issue:
- I add all data AttemptId, Center to one file csv and read from beginning to and end. Using If controller to verify data before action.

Answer 2

1. This statement can be problematic:

   props.put("path_${__threadNum}", String.valueOf(fileName));
   

   as per JSR223 Sampler documentation

   JMeter processes function and variable references before passing the script field to the interpreter, so the references will only be resolved once. Variable and function references in script files will be passed verbatim to the interpreter, which is likely to cause a syntax error. In order to use runtime variables, please use the appropriate props methods, e.g.

   props.get("START.HMS");
   
   props.put("PROP1","1234"); 
   

   So I would recommend replacing ${__threadNum} with ctx.getThreadNum() where ctx is a shorthand for JMeterContext class

2. According to Execution Order chapter of JMeter Documentation:

   0. Configuration elements
   1. Pre-Processors
   2. Timers
   3. Sampler
   4. Post-Processors (unless SampleResult is null)
   5. Assertions (unless SampleResult is null)
   6. Listeners (unless SampleResult is null)
   

   your CSV Data Set Config is executed at the first place, before any other scripting test elements. So the times when it "works" IMO are being caused by "false positive" situation as JMeter Properties are global and "live" while JMeter (and underlying JVM) is running. When you launch JMeter next time the properties will be null and your CSV Data Set Config will fail. So my expectation is that you should consider using __CSVRead() function instead which is evaluated in the runtime exactly in the place where it's being called. Check out Apache JMeter Functions - An Introduction article to learn more about JMeter Functions concept.