How do you crash a JVM?

Question

I was reading a book on programming skills wherein the author asks the interviewee, \"How do you crash a JVM?\" I thought that you could do so by writing an infinite for-loo

Answer 1

Broken hardware can crash any program. I once had an app crash reproducably on a specific machine while running fine on other machines with the exact same setup. Turns out that machine had faulty RAM.

Answer 2

JNI is a large source of crashes. You can also crash using the JVMTI interface since that needs to be written in C/C++ as well.

Answer 3

If you create a thread process that infinitely spawns more threads (which spawn more threads, which...) you'll eventually cause a stack overflow error in the JVM itself.

public class Crash {
    public static void main(String[] args) {

        Runnable[] arr = new Runnable[1];
        arr[0] = () -> {

            while (true) {
                new Thread(arr[0]).start();
            }
        };

        arr[0].run();
    }
}

This gave me the output (after 5 minutes, watch your ram)

An unrecoverable stack overflow has occurred.
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_STACK_OVERFLOW (0xc00000fd) at pc=0x0000000070e53ed7, pid=12840, tid=0x0000000000101078
#
# JRE version: Java(TM) SE Runtime Environment (8.0_144-b01) (build 1.8.0_144-b01)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.144-b01 mixed mode windows-amd64 compressed oops)
# Problematic frame:
# 

Answer 4

I wouldn't call throwing an OutOfMemoryError or StackOverflowError a crash. These are just normal exceptions. To really crash a VM there are 3 ways:

1. Use JNI and crash in the native code.
2. If no security manager is installed you can use reflection to crash the VM. This is VM specific, but normally a VM stores a bunch of pointers to native resources in private fields (e.g. a pointer to the native thread object is stored in a long field in java.lang.Thread). Just change them via reflection and the VM will crash sooner or later.
3. All VMs have bugs, so you just have to trigger one.

For the last method I have a short example, which will crash a Sun Hotspot VM quiet nicely:

public class Crash {
    public static void main(String[] args) {
        Object[] o = null;

        while (true) {
            o = new Object[] {o};
        }
    }
}

This leads to a stack overflow in the GC so you will get no StackOverflowError but a real crash including a hs_err* file.

Answer 5

Running into this issue when trying to replicate the JVM crash.

Jni works, but it needs to be tweaked for different platforms. Eventually, I use this combination to make JVM crash

1. Start the application with this JVM options -XX:+CrashOnOutOfMemoryError
2. Use a long[] l = new long[Integer.MAX_VALUE]; to trigger the OOM

Then JVM will crash and generate the crash log.

Answer 6

A perfect JVM implementation will never crash.

To crash a JVM, aside from JNI, you need to find a bug in the VM itself. An infinite loop just consumes CPU. Infinitely allocating memory should just cause OutOfMemoryError's in a well built JVM. This would probably cause problems for other threads, but a good JVM still should not crash.

If you can find a bug in the source code of the VM, and for example cause a segmentation fault in the memory usage of the implementation of the VM, then you can actually crash it.