The JIT fails to account for native threads when optimizing.

[Guilherme Espada]

The JIT optimizes away a code block because it thinks a value cannot be
changed. But the JIT fails to account for native threads.

Here is some sample code that demonstrates the issue (This example uses
the JNativeHook (https://code.google.com/p/jnativehook/) library):

import org.jnativehook.GlobalScreen;
import org.jnativehook.NativeHookException;
import org.jnativehook.keyboard.NativeKeyEvent;
import org.jnativehook.keyboard.NativeKeyListener;

public class BugTest {

    public static void main(String[] args) {
        try {
            new BugTest().maiin();
        } catch (NativeHookException e) {
            throw new RuntimeException(e);
        }
    }
    class Hook implements NativeKeyListener {
        @Override
        public void nativeKeyPressed(NativeKeyEvent nativeKeyEvent) {
            dirty=true;
            System.out.println("Dirty was set: " + dirty);
        }
        @Override
        public void nativeKeyReleased(NativeKeyEvent nativeKeyEvent) {
        }
        @Override
        public void nativeKeyTyped(NativeKeyEvent nativeKeyEvent) {
        }
    }

    private boolean dirty;

    private void maiin() throws NativeHookException{
        GlobalScreen.registerNativeHook();
        GlobalScreen.getInstance().addNativeKeyListener(new Hook());
        while (true) {
            if(dirty){
                System.out.println("GUIpsp");
            }
        }
    }
}

Expected:
The program should output "GUIpsp" continuously after pressing any key.

Actual:
The program outputs nothing.


This was tested on the following systems:

Linux Satellite-Pro-L500 3.2.0-45-generic #70-Ubuntu SMP x86_64 x86_64
x86_64 GNU/Linux

Windows 7 x64

With the following java -version

java version "1.7.0_21"
OpenJDK Runtime Environment (IcedTea 2.3.9) (7u21-2.3.9-0ubuntu0.12.04.1)
OpenJDK 64-Bit Server VM (build 23.7-b01, mixed mode)

java version "1.7.0_21"
Java(TM) SE Runtime Environment (build 1.7.0_21-b11)
Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode)


As a workaround, adding any activity in the while block prevents the JIT
from optimizing away the block. For example:

        while (true) {
            System.out.toString();
            if(dirty){
                System.out.println("GUIpsp");
            }
        }

Disabling the JIT with -Xint fixes this issue.