Java example source code file (EventHandler.java)

This example Java source code file (EventHandler.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

breakpointevent, classprepareevent, classunloadevent, eventhandler, exceptionevent, interruptedexception, jdi, methodentryevent, methodexitevent, stepevent, threaddeathevent, threadreference, threadstartevent, vmstartevent, watchpointevent

The EventHandler.java Java example source code

/*
 * Copyright (c) 1998, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * This source code is provided to illustrate the usage of a given feature
 * or technique and has been deliberately simplified. Additional steps
 * required for a production-quality application, such as security checks,
 * input validation and proper error handling, might not be present in
 * this sample code.
 */


package com.sun.tools.example.debug.tty;

import com.sun.jdi.*;
import com.sun.jdi.event.*;
import com.sun.jdi.request.EventRequest;

public class EventHandler implements Runnable {

    EventNotifier notifier;
    Thread thread;
    volatile boolean connected = true;
    boolean completed = false;
    String shutdownMessageKey;
    boolean stopOnVMStart;

    EventHandler(EventNotifier notifier, boolean stopOnVMStart) {
        this.notifier = notifier;
        this.stopOnVMStart = stopOnVMStart;
        this.thread = new Thread(this, "event-handler");
        this.thread.start();
    }

    synchronized void shutdown() {
        connected = false;  // force run() loop termination
        thread.interrupt();
        while (!completed) {
            try {wait();} catch (InterruptedException exc) {}
        }
    }

    @Override
    public void run() {
        EventQueue queue = Env.vm().eventQueue();
        while (connected) {
            try {
                EventSet eventSet = queue.remove();
                boolean resumeStoppedApp = false;
                EventIterator it = eventSet.eventIterator();
                while (it.hasNext()) {
                    resumeStoppedApp |= !handleEvent(it.nextEvent());
                }

                if (resumeStoppedApp) {
                    eventSet.resume();
                } else if (eventSet.suspendPolicy() == EventRequest.SUSPEND_ALL) {
                    setCurrentThread(eventSet);
                    notifier.vmInterrupted();
                }
            } catch (InterruptedException exc) {
                // Do nothing. Any changes will be seen at top of loop.
            } catch (VMDisconnectedException discExc) {
                handleDisconnectedException();
                break;
            }
        }
        synchronized (this) {
            completed = true;
            notifyAll();
        }
    }

    private boolean handleEvent(Event event) {
        notifier.receivedEvent(event);

        if (event instanceof ExceptionEvent) {
            return exceptionEvent(event);
        } else if (event instanceof BreakpointEvent) {
            return breakpointEvent(event);
        } else if (event instanceof WatchpointEvent) {
            return fieldWatchEvent(event);
        } else if (event instanceof StepEvent) {
            return stepEvent(event);
        } else if (event instanceof MethodEntryEvent) {
            return methodEntryEvent(event);
        } else if (event instanceof MethodExitEvent) {
            return methodExitEvent(event);
        } else if (event instanceof ClassPrepareEvent) {
            return classPrepareEvent(event);
        } else if (event instanceof ClassUnloadEvent) {
            return classUnloadEvent(event);
        } else if (event instanceof ThreadStartEvent) {
            return threadStartEvent(event);
        } else if (event instanceof ThreadDeathEvent) {
            return threadDeathEvent(event);
        } else if (event instanceof VMStartEvent) {
            return vmStartEvent(event);
        } else {
            return handleExitEvent(event);
        }
    }

    private boolean vmDied = false;
    private boolean handleExitEvent(Event event) {
        if (event instanceof VMDeathEvent) {
            vmDied = true;
            return vmDeathEvent(event);
        } else if (event instanceof VMDisconnectEvent) {
            connected = false;
            if (!vmDied) {
                vmDisconnectEvent(event);
            }
            Env.shutdown(shutdownMessageKey);
            return false;
        } else {
            throw new InternalError(MessageOutput.format("Unexpected event type",
                                                         new Object[] {event.getClass()}));
        }
    }

    synchronized void handleDisconnectedException() {
        /*
         * A VMDisconnectedException has happened while dealing with
         * another event. We need to flush the event queue, dealing only
         * with exit events (VMDeath, VMDisconnect) so that we terminate
         * correctly.
         */
        EventQueue queue = Env.vm().eventQueue();
        while (connected) {
            try {
                EventSet eventSet = queue.remove();
                EventIterator iter = eventSet.eventIterator();
                while (iter.hasNext()) {
                    handleExitEvent(iter.next());
                }
            } catch (InterruptedException exc) {
                // ignore
            } catch (InternalError exc) {
                // ignore
            }
        }
    }

    private ThreadReference eventThread(Event event) {
        if (event instanceof ClassPrepareEvent) {
            return ((ClassPrepareEvent)event).thread();
        } else if (event instanceof LocatableEvent) {
            return ((LocatableEvent)event).thread();
        } else if (event instanceof ThreadStartEvent) {
            return ((ThreadStartEvent)event).thread();
        } else if (event instanceof ThreadDeathEvent) {
            return ((ThreadDeathEvent)event).thread();
        } else if (event instanceof VMStartEvent) {
            return ((VMStartEvent)event).thread();
        } else {
            return null;
        }
    }

    private void setCurrentThread(EventSet set) {
        ThreadReference thread;
        if (set.size() > 0) {
            /*
             * If any event in the set has a thread associated with it,
             * they all will, so just grab the first one.
             */
            Event event = set.iterator().next(); // Is there a better way?
            thread = eventThread(event);
        } else {
            thread = null;
        }
        setCurrentThread(thread);
    }

    private void setCurrentThread(ThreadReference thread) {
        ThreadInfo.invalidateAll();
        ThreadInfo.setCurrentThread(thread);
    }

    private boolean vmStartEvent(Event event)  {
        VMStartEvent se = (VMStartEvent)event;
        notifier.vmStartEvent(se);
        return stopOnVMStart;
    }

    private boolean breakpointEvent(Event event)  {
        BreakpointEvent be = (BreakpointEvent)event;
        notifier.breakpointEvent(be);
        return true;
    }

    private boolean methodEntryEvent(Event event)  {
        MethodEntryEvent me = (MethodEntryEvent)event;
        notifier.methodEntryEvent(me);
        return true;
    }

    private boolean methodExitEvent(Event event)  {
        MethodExitEvent me = (MethodExitEvent)event;
        return notifier.methodExitEvent(me);
    }

    private boolean fieldWatchEvent(Event event)  {
        WatchpointEvent fwe = (WatchpointEvent)event;
        notifier.fieldWatchEvent(fwe);
        return true;
    }

    private boolean stepEvent(Event event)  {
        StepEvent se = (StepEvent)event;
        notifier.stepEvent(se);
        return true;
    }

    private boolean classPrepareEvent(Event event)  {
        ClassPrepareEvent cle = (ClassPrepareEvent)event;
        notifier.classPrepareEvent(cle);

        if (!Env.specList.resolve(cle)) {
            MessageOutput.lnprint("Stopping due to deferred breakpoint errors.");
            return true;
        } else {
            return false;
        }
    }

    private boolean classUnloadEvent(Event event)  {
        ClassUnloadEvent cue = (ClassUnloadEvent)event;
        notifier.classUnloadEvent(cue);
        return false;
    }

    private boolean exceptionEvent(Event event) {
        ExceptionEvent ee = (ExceptionEvent)event;
        notifier.exceptionEvent(ee);
        return true;
    }

    private boolean threadDeathEvent(Event event) {
        ThreadDeathEvent tee = (ThreadDeathEvent)event;
        ThreadInfo.removeThread(tee.thread());
        return false;
    }

    private boolean threadStartEvent(Event event) {
        ThreadStartEvent tse = (ThreadStartEvent)event;
        ThreadInfo.addThread(tse.thread());
        notifier.threadStartEvent(tse);
        return false;
    }

    public boolean vmDeathEvent(Event event) {
        shutdownMessageKey = "The application exited";
        notifier.vmDeathEvent((VMDeathEvent)event);
        return false;
    }

    public boolean vmDisconnectEvent(Event event) {
        shutdownMessageKey = "The application has been disconnected";
        notifier.vmDisconnectEvent((VMDisconnectEvent)event);
        return false;
    }
}