javaScope errorHard

ThreadLocal memory leak in thread pool environment

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BugFind the bug and fix the code

What it should do

Store context in ThreadLocal and return context value. Example: processThreadLocalContext("ctx1") -> "ctx1"

What happens instead

ThreadLocal values persist across tasks in pooled threads, leaking data between users

public class Main {
    private static final ThreadLocal<String> context = new ThreadLocal<>();

    public static String processThreadLocalContext(String val) {
        context.set(val);
        String res = context.get();
        // Omitting context.remove() causes data bleed into future tasks on the same thread
        return res;
    }

    public static void main(String[] args) {
        System.out.println(processThreadLocalContext("ctx1"));
    }
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

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public class Main { private static final ThreadLocal<String> context = new ThreadLocal<>(); public static String processThreadLocalContext(String val) { context.set(val); String res = context.get(); // Omitting context.remove() causes data bleed into future tasks on the same thread return res; } public static void main(String[] args) { System.out.println(processThreadLocalContext("ctx1")); } }

ThreadLocal memory leak in thread pool environment

What it should do

What happens instead

More scope and closure bugs to practise

ThreadLocal memory leak in thread pool environment

What it should do

What happens instead

More scope and closure bugs to practise