title: Ensure vars.get in a JSR223 postprocessor will set value only in current thread
body: <p>In JMeter, I have a Thread Group which has a child JSR223 sampler.
  This JSR223 sampler attempts to execute some code to get a message from a remote system and if it is successful, it sets a variable var1 like so:</p>
  <pre><code>vars.put('var1', var1)
  </code></pre>
  <p>Then, in a child JSR223 PostProcessor of this JSR223 sampler, I do:</p>
  <pre><code>var1 = vars.get('var1')
  </code></pre>
  <p>Then I use var1 for some calculations to amend the parent JSR223 sampler results.</p>
  <p>I am concerned that if I spawn multiple concurrent threads with this code, they will each try to put a value into var1 and then when the PostProcessor will run, I will not have a guarantee that the var1 value which I am trying to use in the postprocessor, is actually the var1 value set by the current thread parent sampler. Could it be the value set by another thread?</p>
  <p>Is this a valid concern, and if yes, how can I mitigate it?</p>
  <p>Thanks in advance!</p>