AppContext is null from rmi thread with Java 7 Update 25

Question

We recently updated to Java 7 Update 25 from Update 21 and are now experiencing a null pointer exception when SwingUtilities.isEventDispatchThread() is called from an rmi thread becuase AppContext.getAppContext() is returning null.

java.lang.NullPointerException at sun.awt.SunToolkit.getSystemEventQueueImplPP(Unknown Source) at sun.awt.SunToolkit.getSystemEventQueueImplPP(Unknown Source) at sun.awt.SunToolkit.getSystemEventQueueImpl(Unknown Source) at java.awt.Toolkit.getEventQueue(Unknown Source) at java.awt.EventQueue.isDispatchThread(Unknown Source) at javax.swing.SwingUtilities.isEventDispatchThread(Unknown Source) at ... ... at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Unknown Source) at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)

This error is only present from web start, when we run our application through an IDE, it is fine.

Has anyone else ran into this? Any idea of what was changed in the latest update regarding AppContext?

It seems others are having somewhat related issues with AppContext after the update: https://forums.oracle.com/message/11077767#11077767

Abbeyabbi

I can't provide a solution, but we have the same problem with Java 7 Update 25. We have a Swing-based application that is distributed and started with Java Webstart. It also acts as a RMI server. When an incoming RMI invocation calls EventQueue.isDispatchThread, we get the same exception: sun.awt.AppContext#getAppContext() seems to return null in this situation. It's a serious regression that makes Java 7 Update 25 useless for our application. When trying to apply the workaround from Bug 4711515 we get a step further. But then the Nullpointer problem in JNLPClassLoader.getPermissions occurs... – Lapp

The Nullpointer problem in JNLPClassLoader.getPermissons() is mentioned here: #17231273 There is something seriously wrong that update release... – Lapp

We have probably similar problem here: <#17275759> . In our application the client also acts as a RMI server. – Cerelia

Answer 1

I had the same problem with Java3D running as Java Web Start. I have found another solution. You have to prepare you own InvokeLaterProcessor with queue of runnables. It must extend Thread and pick ups runnables and process them in run method:

public class InvokeLaterProcessor extends Thread {

  private BlockingQueue<Runnable> queue=new ArrayBlockingQueue<Runnable>(1);

  public InvokeLaterProcessor(String name) {
    super(name);
  }

  public void invokeLater(Runnable runnable) {
    try {
      queue.put(runnable);
    } catch (InterruptedException ex) {
      log.warn("invokeLater interrupted");
    }
  }

  public void run() {
    Runnable runnable=null;
    do {
      try {
        runnable = queue.take();
        SwingUtilities.invokeLater(runnable);
      } catch (InterruptedException ex) {
        runnable=null;
      }
    } while(runnable!=null);
  }
}

Than all you have to do is create it in static of some class which is created in main thread:

static {
  invokeLaterProcessor=new InvokeLaterProcessor("MyInvokeLater");
  invokeLaterProcessor.start();
}

and process runnables by this code:

invokeLaterProcessor.invokeLater(runnable);

You don't need proprietary

sun.awt.SunToolkit.invokeLaterOnAppContext(evtContext, rn)

Harder

Answer 2

It is not a final answer but it is a workaround, that works for me.

The application need to save the current AppContext in EVT:

  AppContext evtContext; //field

  SwingUtilities.invokeLater(new Runnable() {
      public void run() {
          evtContext = AppContext.getAppContext();
      }
  });

Then all the calls to SwingUtilities.invokeLater(..) from RMI threads must be replaced with custom invokeLater2(Runnable rn) method that uses sun.awt.SunToolkit.invokeLaterOnAppContext(..,..) like:

void invokeLater2(Runnable rn) {
    if (AppContext.getAppContext() == null) {
        logger.warning("AppContext is null, using EVT AppContext"
          + " through SunToolKit");
        sun.awt.SunToolkit.invokeLaterOnAppContext(evtContext, rn);
    } else {
        SwingUtilities.invokeLater(rn);
    }
}

Unfortunately all the calls to SwingUtilities.invokeLater(..) from RMI threads must be replaced and the program now depends on internal Sun JRE proprietary API.

I hope Oracle will provide patches for the JRE 1.7.0.u25 soon to address this problem.

-- This workaround was made under suggestions from guruman in the comments here.

Cerelia

1) I have to compile my code using java 5 and it gives me error when I tried to use sun.awt.SunToolkit.invokeLaterOnAppContext, was this something that was added after Java 5? 2) I tried the approach of creating a thread belonging to a particular thread group and it worked but I cant really use this approach since I will end up creating a lot of threads. 2.1) Is there a way to assign to create a single thread and assign tasks to it 2.2) IS there a way to assign tasks to the EDT without using invokeLater and invokeAndWait – Sg

Actually I use java 1.7.0 Update 21. I did not check the code on previous java releases. This the reason I personally don't like to use internal JRE classes. – Cerelia

Answer 3

Here is a workaround for JDK-8019274, packaged in a utility class.

For us, invokeAndWait() was the big issue. This example has the existing fix for invokeLater() and a new fix for invokeAndWait().

Notes:

• You'll need jnlp.jar
• Call init() early in your main() method, before calling invokeLater()!
• Replace all calls to invokeLater() and invokeAndWait() with these calls

(Disclaimer: This is from our product. Some aspects of this solution may not apply to you.)

public class JreFix {
    private static String badVersionInfo = null;
    private static AppContext awtEventDispatchContext = null;
    private static AppContext mainThreadContext = null;
    private static Boolean isWebStart = null;
    private static BasicService basicService = null;
    private static IntegrationService integrationService = null;

    /**
     * Call this early in main().  
     */
    public static void init() {
        if (isWebstart() && isApplicableJvmType()) {
            String javaVersion = System.getProperty("java.version");

            if ("1.7.0_25".equals(javaVersion)) {
                badVersionInfo = "7u25";
            }
            else if ("1.7.0_40".equals(javaVersion)) {
                badVersionInfo = "7u40";
            }
            else if (javaVersion != null && "1.6.0_51".equals(javaVersion.substring(0,8))) {
                badVersionInfo = "6u51";
            }
            else if ("javaws-10.25.2.16".equals(System.getProperty("javawebstart.version"))) {
                badVersionInfo = "Web Start 10.25.2.16";
            }
        }

        if (badVersionInfo != null) {
            mainThreadContext = AppContext.getAppContext();
            try {
                SwingUtilities.invokeAndWait(new Runnable() {
                    public void run() {
                        awtEventDispatchContext = AppContext.getAppContext();
                    }
                });
            }
            catch (Exception e) {
                displayErrorAndExit(null);
            }

            if (mainThreadContext == null || awtEventDispatchContext == null) {
                 displayErrorAndExit(null);
            }
        }
    }

    public static void invokeNowOrLater(Runnable runnable) {
        if (hasAppContextBug()) {
            invokeLaterOnAwtEventDispatchThreadContext(runnable);
        }
        else {
            SwingUtilities.invokeLater(runnable);
        }
    }

    public static void invokeNowOrWait(Runnable runnable) {
        if (hasAppContextBug()) {
            fixThreadAppContext(null);
        }

        try {
            SwingUtilities.invokeAndWait(runnable);
        } 
        catch (Exception e) {
            // handle it
        }
    }

    public static boolean hasAppContextBug() {
        return isJreWithAppContextBug() && AppContext.getAppContext() == null;
    }

    public static void invokeLaterOnAwtEventDispatchThreadContext(Runnable runnable) {
        sun.awt.SunToolkit.invokeLaterOnAppContext(awtEventDispatchContext, runnable);
    }

    public static void fixThreadAppContext(Component parent) {
        try {
            final Field field = AppContext.class.getDeclaredField("threadGroup2appContext");
            field.setAccessible(true);
            Map<ThreadGroup, AppContext> threadGroup2appContext = (Map<ThreadGroup, AppContext>)field.get(null);
            final ThreadGroup currentThreadGroup = Thread.currentThread().getThreadGroup();
            threadGroup2appContext.put(currentThreadGroup, mainThreadContext);
        } 
        catch (Exception e) {
            displayErrorAndExit(parent);
        }

        if (AppContext.getAppContext() == null) {
             displayErrorAndExit(parent);
        }
    }

    private static boolean isJreWithAppContextBug() {
        return badVersionInfo != null;
    }

    private static void displayErrorAndExit(Component parent) {
        JLabel msgLabel = new JLabel("<html>" + 
                "Our application cannot run using <b>Web Start</b> with this version of Java.<p><p>" +
                "Java " + badVersionInfo + " contains a bug acknowledged by Oracle (JDK-8019274).");
        JOptionPane.showMessageDialog(parent, msgLabel, "Java Version Error", JOptionPane.ERROR_MESSAGE);
        System.exit(1);
    }

    private static boolean isApplicableJvmType() {
        String vendor = System.getProperty("java.vendor");
        String vmName = System.getProperty("java.vm.name");
        if (vendor != null && vmName != null) {
            return vmName.contains("Java HotSpot") &&
                    (vendor.equals("Oracle Corporation") || 
                     vendor.equals("Sun Microsystems Inc."));
        }

        return false;
    }

    private static boolean isWebstart() {
        if (isWebStart == null) {
            try { 
                basicService = (BasicService) ServiceManager.lookup("javax.jnlp.BasicService");             
                isWebStart = true;
            } 
            catch (UnavailableServiceException e) { 
                isWebStart = false;
            }           

            try {
                integrationService = (IntegrationService) ServiceManager.lookup("javax.jnlp.IntegrationService");
            } 
            catch (UnavailableServiceException e) {
            }
        }
        return isWebStart;
    }
}

Boony