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Java Survival Kit

Heap dump vs thread dump vs core dump

Heap dump

JVM creates the heap which contains references to objects in use at runtime. Heap dump is a saved copy of the current state of all objects in use at runtime.

Heap dumps is helpful when analyzing scenario like OutOfMemoryError.

public class Main {
    public static void main(String[] args) {
        List<Integer> nums = new ArrayList<>();
        try {
            while (true) {
                nums.add(10);
            }
        } catch (OutOfMemoryError e) {
            System.out.println("Out of memory error occurred!");
        }
    }
}

To capture heap dump use tools like jmap.

Thread dump

Thread dump contains the snapshot of all threads in a running Java program at a specific instant. Thread dump is helpful for analyzing performance issues (detecting threads stuck in an infinite loop, deadlocks where multiple threads are waiting for one other to release resources, threads not getting enough CPU time).

public class ThreadDump {
    public static void main(String[] args) {
        longRunningTask();
    }


    private static void longRunningTask() {
        for (int i = 0; i < Integer.MAX_VALUE; i++) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("Interrupted!");
                break;
            }
            System.out.println(i);
        }
    }
}

References