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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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package com.sun.tools.jdi;

import com.sun.jdi.*;

import java.lang.ref.WeakReference;
import java.util.*;

class VMState {
    private final VirtualMachineImpl vm;

    // Listeners
    private final List<WeakReference> listeners = new ArrayList<WeakReference>(); // synchronized (this)
    private boolean notifyingListeners = false;  // synchronized (this)

    /*
     * Certain information can be cached only when the entire VM is
     * suspended and there are no pending resumes. The fields below
     * are used to track whether there are pending resumes. (There
     * is an assumption that JDWP command ids are increasing over time.)
     */
    private int lastCompletedCommandId = 0;   // synchronized (this)
    private int lastResumeCommandId = 0;      // synchronized (this)

    // This is cached only while the VM is suspended
    private static class Cache {
        List<ThreadGroupReference> groups = null;  // cached Top Level ThreadGroups
        List<ThreadReference> threads = null; // cached Threads
    }

    private Cache cache = null;               // synchronized (this)
    private static final Cache markerCache = new Cache();

    private void disableCache() {
        synchronized (this) {
            cache = null;
        }
    }

    private void enableCache() {
        synchronized (this) {
            cache = markerCache;
        }
    }

    private Cache getCache() {
        synchronized (this) {
            if (cache == markerCache) {
                cache = new Cache();
            }
            return cache;
        }
    }

    VMState(VirtualMachineImpl vm) {
        this.vm = vm;
    }

    
Is the VM currently suspended, for the purpose of caching? Must be called synchronized on vm.state()
/** * Is the VM currently suspended, for the purpose of caching? * Must be called synchronized on vm.state() */
boolean isSuspended() { return cache != null; } /* * A JDWP command has been completed (reply has been received). * Update data that tracks pending resume commands. */ synchronized void notifyCommandComplete(int id) { lastCompletedCommandId = id; } synchronized void freeze() { if (cache == null && (lastCompletedCommandId >= lastResumeCommandId)) { /* * No pending resumes to worry about. The VM is suspended * and additional state can be cached. Notify all * interested listeners. */ processVMAction(new VMAction(vm, VMAction.VM_SUSPENDED)); enableCache(); } } synchronized PacketStream thawCommand(CommandSender sender) { PacketStream stream = sender.send(); lastResumeCommandId = stream.id(); thaw(); return stream; }
All threads are resuming
/** * All threads are resuming */
void thaw() { thaw(null); }
Tell listeners to invalidate suspend-sensitive caches. If resumingThread != null, then only that thread is being resumed.
/** * Tell listeners to invalidate suspend-sensitive caches. * If resumingThread != null, then only that thread is being * resumed. */
synchronized void thaw(ThreadReference resumingThread) { if (cache != null) { if ((vm.traceFlags & vm.TRACE_OBJREFS) != 0) { vm.printTrace("Clearing VM suspended cache"); } disableCache(); } processVMAction(new VMAction(vm, resumingThread, VMAction.VM_NOT_SUSPENDED)); } private synchronized void processVMAction(VMAction action) { if (!notifyingListeners) { // Prevent recursion notifyingListeners = true; Iterator iter = listeners.iterator(); while (iter.hasNext()) { WeakReference ref = (WeakReference)iter.next(); VMListener listener = (VMListener)ref.get(); if (listener != null) { boolean keep = true; switch (action.id()) { case VMAction.VM_SUSPENDED: keep = listener.vmSuspended(action); break; case VMAction.VM_NOT_SUSPENDED: keep = listener.vmNotSuspended(action); break; } if (!keep) { iter.remove(); } } else { // Listener is unreachable; clean up iter.remove(); } } notifyingListeners = false; } } synchronized void addListener(VMListener listener) { listeners.add(new WeakReference<VMListener>(listener)); } synchronized boolean hasListener(VMListener listener) { return listeners.contains(listener); } synchronized void removeListener(VMListener listener) { Iterator iter = listeners.iterator(); while (iter.hasNext()) { WeakReference ref = (WeakReference)iter.next(); if (listener.equals(ref.get())) { iter.remove(); break; } } } List<ThreadReference> allThreads() { List<ThreadReference> threads = null; try { Cache local = getCache(); if (local != null) { // may be stale when returned, but not provably so threads = local.threads; } if (threads == null) { threads = Arrays.asList((ThreadReference[])JDWP.VirtualMachine.AllThreads. process(vm).threads); if (local != null) { local.threads = threads; if ((vm.traceFlags & vm.TRACE_OBJREFS) != 0) { vm.printTrace("Caching all threads (count = " + threads.size() + ") while VM suspended"); } } } } catch (JDWPException exc) { throw exc.toJDIException(); } return threads; } List<ThreadGroupReference> topLevelThreadGroups() { List<ThreadGroupReference> groups = null; try { Cache local = getCache(); if (local != null) { groups = local.groups; } if (groups == null) { groups = Arrays.asList( (ThreadGroupReference[])JDWP.VirtualMachine.TopLevelThreadGroups. process(vm).groups); if (local != null) { local.groups = groups; if ((vm.traceFlags & vm.TRACE_OBJREFS) != 0) { vm.printTrace( "Caching top level thread groups (count = " + groups.size() + ") while VM suspended"); } } } } catch (JDWPException exc) { throw exc.toJDIException(); } return groups; } }