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 com.sun.jdi.*;
29
30 import java.lang.ref.WeakReference;
31 import java.util.*;
32
33 class VMState {
34 private final VirtualMachineImpl vm;
35
36 // Listeners
37 private final List<WeakReference<VMListener>> listeners = new ArrayList<WeakReference<VMListener>>(); // synchronized (this)
38 private boolean notifyingListeners = false; // synchronized (this)
39
40 /*
41 * Certain information can be cached only when the entire VM is
42 * suspended and there are no pending resumes. The field below
43 * is used to track whether there are pending resumes.
44 */
45 private final Set<Integer> pendingResumeCommands = Collections.synchronizedSet(new HashSet<>());
46
47 // This is cached only while the VM is suspended
48 private static class Cache {
49 List<ThreadGroupReference> groups = null; // cached Top Level ThreadGroups
50 List<ThreadReference> threads = null; // cached Threads
51 }
52
53 private Cache cache = null; // synchronized (this)
54 private static final Cache markerCache = new Cache();
55
56 private void disableCache() {
57 synchronized (this) {
58 cache = null;
59 }
60 }
61
62 private void enableCache() {
63 synchronized (this) {
64 cache = markerCache;
65 }
66 }
67
68 private Cache getCache() {
69 synchronized (this) {
70 if (cache == markerCache) {
71 cache = new Cache();
72 }
73 return cache;
74 }
75 }
76
77 VMState(VirtualMachineImpl vm) {
78 this.vm = vm;
79 }
80
81 /**
82 * Is the VM currently suspended, for the purpose of caching?
83 * Must be called synchronized on vm.state()
84 */
85 boolean isSuspended() {
86 return cache != null;
87 }
88
89 /*
90 * A JDWP command has been completed (reply has been received).
91 * Update data that tracks pending resume commands.
92 */
93 void notifyCommandComplete(int id) {
94 pendingResumeCommands.remove(id);
95 }
96
97 synchronized void freeze() {
98 if (cache == null && (pendingResumeCommands.isEmpty())) {
99 /*
100 * No pending resumes to worry about. The VM is suspended
101 * and additional state can be cached. Notify all
102 * interested listeners.
103 */
104 processVMAction(new VMAction(vm, VMAction.VM_SUSPENDED));
105 enableCache();
106 }
107 }
108
109 synchronized PacketStream thawCommand(CommandSender sender) {
110 PacketStream stream = sender.send();
111 pendingResumeCommands.add(stream.id());
112 thaw();
113 return stream;
114 }
115
116 /**
117 * All threads are resuming
118 */
119 void thaw() {
120 thaw(null);
121 }
122
123 /**
124 * Tell listeners to invalidate suspend-sensitive caches.
125 * If resumingThread != null, then only that thread is being
126 * resumed.
127 */
128 synchronized void thaw(ThreadReference resumingThread) {
129 if (cache != null) {
130 if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
131 vm.printTrace("Clearing VM suspended cache");
132 }
133 disableCache();
134 }
135 processVMAction(new VMAction(vm, resumingThread, VMAction.VM_NOT_SUSPENDED));
136 }
137
138 private synchronized void processVMAction(VMAction action) {
139 if (!notifyingListeners) {
140 // Prevent recursion
141 notifyingListeners = true;
142
143 Iterator<WeakReference<VMListener>> iter = listeners.iterator();
144 while (iter.hasNext()) {
145 WeakReference<VMListener> ref = iter.next();
146 VMListener listener = ref.get();
147 if (listener != null) {
148 boolean keep = true;
149 switch (action.id()) {
150 case VMAction.VM_SUSPENDED:
151 keep = listener.vmSuspended(action);
152 break;
153 case VMAction.VM_NOT_SUSPENDED:
154 keep = listener.vmNotSuspended(action);
155 break;
156 }
157 if (!keep) {
158 iter.remove();
159 }
160 } else {
161 // Listener is unreachable; clean up
162 iter.remove();
163 }
164 }
165
166 notifyingListeners = false;
167 }
168 }
169
170 synchronized void addListener(VMListener listener) {
171 listeners.add(new WeakReference<VMListener>(listener));
172 }
173
174 synchronized boolean hasListener(VMListener listener) {
175 return listeners.contains(listener);
176 }
177
178 synchronized void removeListener(VMListener listener) {
179 Iterator<WeakReference<VMListener>> iter = listeners.iterator();
180 while (iter.hasNext()) {
181 WeakReference<VMListener> ref = iter.next();
182 if (listener.equals(ref.get())) {
183 iter.remove();
184 break;
185 }
186 }
187 }
188
189 List<ThreadReference> allThreads() {
190 List<ThreadReference> threads = null;
191 try {
192 Cache local = getCache();
193
194 if (local != null) {
195 // may be stale when returned, but not provably so
196 threads = local.threads;
197 }
198 if (threads == null) {
199 threads = Arrays.asList((ThreadReference[])JDWP.VirtualMachine.AllThreads.
200 process(vm).threads);
201 if (local != null) {
202 local.threads = threads;
203 if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
204 vm.printTrace("Caching all threads (count = " +
205 threads.size() + ") while VM suspended");
206 }
207 }
208 }
209 } catch (JDWPException exc) {
210 throw exc.toJDIException();
211 }
212 return threads;
213 }
214
215
216 List<ThreadGroupReference> topLevelThreadGroups() {
217 List<ThreadGroupReference> groups = null;
218 try {
219 Cache local = getCache();
220
221 if (local != null) {
222 groups = local.groups;
223 }
224 if (groups == null) {
225 groups = Arrays.asList(
226 (ThreadGroupReference[])JDWP.VirtualMachine.TopLevelThreadGroups.
227 process(vm).groups);
228 if (local != null) {
229 local.groups = groups;
230 if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
231 vm.printTrace(
232 "Caching top level thread groups (count = " +
233 groups.size() + ") while VM suspended");
234 }
235 }
236 }
237 } catch (JDWPException exc) {
238 throw exc.toJDIException();
239 }
240 return groups;
241 }
242
243 }