How do you troubleshoot inconsistent results from a BeanShell script sharing global variables?

Identify whether the variable causing inconsistent behavior is actually a JMeter property (props), which is genuinely shared across every thread, versus a JMeter thread variable (vars), which should be isolated per thread - a common root cause of this exact symptom is a script mistakenly using props for data that was actually meant to be thread-local.

If props genuinely needs to be shared and mutated across threads, like a running counter, check for race conditions from concurrent threads reading and writing it without any coordination, since JMeter doesn't automatically synchronize access to a shared property just because multiple threads happen to reference the same property name concurrently.

Check whether the script itself is referencing a variable at the Java language level that's actually static or otherwise shared beyond BeanShell's own namespace mechanism - a static field on a class the script imports and uses would be shared across every thread and every Interpreter instance, independent of anything BeanShell-specific, and behaves exactly as it would in any other multi-threaded Java code.

Add explicit, deliberate synchronization, like Java's synchronized keyword or an atomic type, around any genuinely shared, mutable state the script needs to touch, treating this exactly as you would any other multi-threaded Java programming problem, since BeanShell running inside JMeter's multi-threaded execution model doesn't provide any automatic thread-safety guarantees beyond what the underlying Java constructs the script uses actually provide.

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