1 /*
   2  * Copyright (c) 1999, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package com.sun.tools.jdi;
  27 
  28 import java.lang.ref.WeakReference;
  29 import java.util.*;
  30 
  31 import com.sun.jdi.ThreadGroupReference;
  32 import com.sun.jdi.ThreadReference;
  33 import com.sun.jdi.VirtualMachine;
  34 
  35 class VMState {
  36     private final VirtualMachineImpl vm;
  37 
  38     // Listeners
  39     private final List<WeakReference<VMListener>> listeners = new ArrayList<>(); // synchronized (this)
  40     private boolean notifyingListeners = false;  // synchronized (this)
  41 
  42     /*
  43      * Certain information can be cached only when the entire VM is
  44      * suspended and there are no pending resumes. The field below
  45      * is used to track whether there are pending resumes.
  46      */
  47     private final Set<Integer> pendingResumeCommands = Collections.synchronizedSet(new HashSet<>());
  48 
  49     // This is cached only while the VM is suspended
  50     private static class Cache {
  51         List<ThreadGroupReference> groups = null;  // cached Top Level ThreadGroups
  52         List<ThreadReference> threads = null; // cached Threads
  53     }
  54 
  55     private Cache cache = null;               // synchronized (this)
  56     private static final Cache markerCache = new Cache();
  57 
  58     private void disableCache() {
  59         synchronized (this) {
  60             cache = null;
  61         }
  62     }
  63 
  64     private void enableCache() {
  65         synchronized (this) {
  66             cache = markerCache;
  67         }
  68     }
  69 
  70     private Cache getCache() {
  71         synchronized (this) {
  72             if (cache == markerCache) {
  73                 cache = new Cache();
  74             }
  75             return cache;
  76         }
  77     }
  78 
  79     VMState(VirtualMachineImpl vm) {
  80         this.vm = vm;
  81     }
  82 
  83     /**
  84      * Is the VM currently suspended, for the purpose of caching?
  85      * Must be called synchronized on vm.state()
  86      */
  87     boolean isSuspended() {
  88         return cache != null;
  89     }
  90 
  91     /*
  92      * A JDWP command has been completed (reply has been received).
  93      * Update data that tracks pending resume commands.
  94      */
  95     void notifyCommandComplete(int id) {
  96         pendingResumeCommands.remove(id);
  97     }
  98 
  99     synchronized void freeze() {
 100         if (cache == null && (pendingResumeCommands.isEmpty())) {
 101             /*
 102              * No pending resumes to worry about. The VM is suspended
 103              * and additional state can be cached. Notify all
 104              * interested listeners.
 105              */
 106             processVMAction(new VMAction(vm, VMAction.VM_SUSPENDED));
 107             enableCache();
 108         }
 109     }
 110 
 111     synchronized PacketStream thawCommand(CommandSender sender) {
 112         PacketStream stream = sender.send();
 113         pendingResumeCommands.add(stream.id());
 114         thaw();
 115         return stream;
 116     }
 117 
 118     /**
 119      * All threads are resuming
 120      */
 121     void thaw() {
 122         thaw(null);
 123     }
 124 
 125     /**
 126      * Tell listeners to invalidate suspend-sensitive caches.
 127      * If resumingThread != null, then only that thread is being
 128      * resumed.
 129      */
 130     synchronized void thaw(ThreadReference resumingThread) {
 131         if (cache != null) {
 132             if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
 133                 vm.printTrace("Clearing VM suspended cache");
 134             }
 135             disableCache();
 136         }
 137         processVMAction(new VMAction(vm, resumingThread, VMAction.VM_NOT_SUSPENDED));
 138     }
 139 
 140     private synchronized void processVMAction(VMAction action) {
 141         if (!notifyingListeners) {
 142             // Prevent recursion
 143             notifyingListeners = true;
 144 
 145             Iterator<WeakReference<VMListener>> iter = listeners.iterator();
 146             while (iter.hasNext()) {
 147                 WeakReference<VMListener> ref = iter.next();
 148                 VMListener listener = ref.get();
 149                 if (listener != null) {
 150                     boolean keep = true;
 151                     switch (action.id()) {
 152                         case VMAction.VM_SUSPENDED:
 153                             keep = listener.vmSuspended(action);
 154                             break;
 155                         case VMAction.VM_NOT_SUSPENDED:
 156                             keep = listener.vmNotSuspended(action);
 157                             break;
 158                     }
 159                     if (!keep) {
 160                         iter.remove();
 161                     }
 162                 } else {
 163                     // Listener is unreachable; clean up
 164                     iter.remove();
 165                 }
 166             }
 167 
 168             notifyingListeners = false;
 169         }
 170     }
 171 
 172     synchronized void addListener(VMListener listener) {
 173         listeners.add(new WeakReference<VMListener>(listener));
 174     }
 175 
 176     synchronized boolean hasListener(VMListener listener) {
 177         return listeners.contains(listener);
 178     }
 179 
 180     synchronized void removeListener(VMListener listener) {
 181         Iterator<WeakReference<VMListener>> iter = listeners.iterator();
 182         while (iter.hasNext()) {
 183             WeakReference<VMListener> ref = iter.next();
 184             if (listener.equals(ref.get())) {
 185                 iter.remove();
 186                 break;
 187             }
 188         }
 189     }
 190 
 191     List<ThreadReference> allThreads() {
 192         List<ThreadReference> threads = null;
 193         try {
 194             Cache local = getCache();
 195 
 196             if (local != null) {
 197                 // may be stale when returned, but not provably so
 198                 threads = local.threads;
 199             }
 200             if (threads == null) {
 201                 threads = Arrays.asList((ThreadReference[])JDWP.VirtualMachine.AllThreads.
 202                                         process(vm).threads);
 203                 if (local != null) {
 204                     local.threads = threads;
 205                     if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
 206                         vm.printTrace("Caching all threads (count = " +
 207                                       threads.size() + ") while VM suspended");
 208                     }
 209                 }
 210             }
 211         } catch (JDWPException exc) {
 212             throw exc.toJDIException();
 213         }
 214         return threads;
 215     }
 216 
 217 
 218     List<ThreadGroupReference> topLevelThreadGroups() {
 219         List<ThreadGroupReference> groups = null;
 220         try {
 221             Cache local = getCache();
 222 
 223             if (local != null) {
 224                 groups = local.groups;
 225             }
 226             if (groups == null) {
 227                 groups = Arrays.asList(
 228                                 (ThreadGroupReference[])JDWP.VirtualMachine.TopLevelThreadGroups.
 229                                        process(vm).groups);
 230                 if (local != null) {
 231                     local.groups = groups;
 232                     if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
 233                         vm.printTrace(
 234                           "Caching top level thread groups (count = " +
 235                           groups.size() + ") while VM suspended");
 236                     }
 237                 }
 238             }
 239         } catch (JDWPException exc) {
 240             throw exc.toJDIException();
 241         }
 242         return groups;
 243     }
 244 }