javaAsync race conditionMedium

ExecutorService thread pool prevents JVM shutdown

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BugFind the bug and fix the code

What it should do

Submit task to executor and return completed value. Example: executeBackgroundTask(10) -> 10

What happens instead

Application hangs on shutdown because non-daemon ExecutorService was never shut down

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class Main {
    public static int executeBackgroundTask(int val) throws Exception {
        ExecutorService executor = Executors.newSingleThreadExecutor();
        Future<Integer> future = executor.submit(() -> val);
        int result = future.get();
        // Missing executor.shutdown() keeps non-daemon thread pool worker alive forever
        return result;
    }

    public static void main(String[] args) throws Exception {
        System.out.println(executeBackgroundTask(10));
    }
}

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 async and race conditions pattern

A missing await, unbuffered channel deadlocks, ConcurrentModificationException, and data races under load.

Learn the async and race conditions pattern Step through your own code

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import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; public class Main { public static int executeBackgroundTask(int val) throws Exception { ExecutorService executor = Executors.newSingleThreadExecutor(); Future<Integer> future = executor.submit(() -> val); int result = future.get(); // Missing executor.shutdown() keeps non-daemon thread pool worker alive forever return result; } public static void main(String[] args) throws Exception { System.out.println(executeBackgroundTask(10)); } }

ExecutorService thread pool prevents JVM shutdown

What it should do

What happens instead

More async and race conditions to practise

ExecutorService thread pool prevents JVM shutdown

What it should do

What happens instead

More async and race conditions to practise