1 /*
2 * Copyright (c) 1996, 2005, 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 package sun.rmi.transport;
26
27 import java.lang.ref.ReferenceQueue;
28 import java.rmi.NoSuchObjectException;
29 import java.rmi.Remote;
30 import java.rmi.dgc.VMID;
31 import java.rmi.server.ExportException;
32 import java.rmi.server.ObjID;
33 import java.security.AccessController;
34 import java.security.PrivilegedAction;
35 import java.util.HashMap;
36 import java.util.Map;
37 import sun.misc.GC;
38 import sun.rmi.runtime.Log;
39 import sun.rmi.runtime.NewThreadAction;
40 import sun.security.action.GetLongAction;
41
42 /**
43 * Object table shared by all implementors of the Transport interface.
44 * This table maps object ids to remote object targets in this address
45 * space.
46 *
47 * @author Ann Wollrath
48 * @author Peter Jones
49 */
50 public final class ObjectTable {
51
52 /** maximum interval between complete garbage collections of local heap */
53 private final static long gcInterval = // default 1 hour
54 AccessController.doPrivileged(
55 new GetLongAction("sun.rmi.dgc.server.gcInterval", 3600000));
56
57 /**
58 * lock guarding objTable and implTable.
59 * Holders MAY acquire a Target instance's lock or keepAliveLock.
60 */
61 private static final Object tableLock = new Object();
62
63 /** tables mapping to Target, keyed from ObjectEndpoint and impl object */
64 private static final Map<ObjectEndpoint,Target> objTable =
65 new HashMap<ObjectEndpoint,Target>();
66 private static final Map<WeakRef,Target> implTable =
67 new HashMap<WeakRef,Target>();
68
69 /**
70 * lock guarding keepAliveCount, reaper, and gcLatencyRequest.
71 * Holders may NOT acquire a Target instance's lock or tableLock.
72 */
73 private static final Object keepAliveLock = new Object();
74
75 /** count of non-permanent objects in table or still processing calls */
76 private static int keepAliveCount = 0;
77
78 /** thread to collect unreferenced objects from table */
79 private static Thread reaper = null;
80
81 /** queue notified when weak refs in the table are cleared */
82 static final ReferenceQueue reapQueue = new ReferenceQueue();
83
84 /** handle for GC latency request (for future cancellation) */
85 private static GC.LatencyRequest gcLatencyRequest = null;
86
87 /*
88 * Disallow anyone from creating one of these.
89 */
90 private ObjectTable() {}
91
92 /**
93 * Returns the target associated with the object id.
94 */
95 static Target getTarget(ObjectEndpoint oe) {
96 synchronized (tableLock) {
97 return objTable.get(oe);
98 }
99 }
100
101 /**
102 * Returns the target associated with the remote object
103 */
104 public static Target getTarget(Remote impl) {
105 synchronized (tableLock) {
106 return implTable.get(new WeakRef(impl));
107 }
108 }
109
110 /**
111 * Returns the stub for the remote object <b>obj</b> passed
112 * as a parameter. This operation is only valid <i>after</i>
113 * the object has been exported.
114 *
115 * @return the stub for the remote object, <b>obj</b>.
116 * @exception NoSuchObjectException if the stub for the
117 * remote object could not be found.
118 */
119 public static Remote getStub(Remote impl)
120 throws NoSuchObjectException
121 {
122 Target target = getTarget(impl);
123 if (target == null) {
124 throw new NoSuchObjectException("object not exported");
125 } else {
126 return target.getStub();
127 }
128 }
129
130 /**
131 * Remove the remote object, obj, from the RMI runtime. If
132 * successful, the object can no longer accept incoming RMI calls.
133 * If the force parameter is true, the object is forcibly unexported
134 * even if there are pending calls to the remote object or the
135 * remote object still has calls in progress. If the force
136 * parameter is false, the object is only unexported if there are
137 * no pending or in progress calls to the object.
138 *
139 * @param obj the remote object to be unexported
140 * @param force if true, unexports the object even if there are
141 * pending or in-progress calls; if false, only unexports the object
142 * if there are no pending or in-progress calls
143 * @return true if operation is successful, false otherwise
144 * @exception NoSuchObjectException if the remote object is not
145 * currently exported
146 */
147 public static boolean unexportObject(Remote obj, boolean force)
148 throws java.rmi.NoSuchObjectException
149 {
150 synchronized (tableLock) {
151 Target target = getTarget(obj);
152 if (target == null) {
153 throw new NoSuchObjectException("object not exported");
154 } else {
155 if (target.unexport(force)) {
156 removeTarget(target);
157 return true;
158 } else {
159 return false;
160 }
161 }
162 }
163 }
164
165 /**
166 * Add target to object table. If it is not a permanent entry, then
167 * make sure that reaper thread is running to remove collected entries
168 * and keep VM alive.
169 */
170 static void putTarget(Target target) throws ExportException {
171 ObjectEndpoint oe = target.getObjectEndpoint();
172 WeakRef weakImpl = target.getWeakImpl();
173
174 if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) {
175 DGCImpl.dgcLog.log(Log.VERBOSE, "add object " + oe);
176 }
177
178 Remote impl = target.getImpl();
179 if (impl == null) {
180 throw new ExportException(
181 "internal error: attempt to export collected object");
182 }
183
184 synchronized (tableLock) {
185 if (objTable.containsKey(oe)) {
186 throw new ExportException(
187 "internal error: ObjID already in use");
188 } else if (implTable.containsKey(weakImpl)) {
189 throw new ExportException("object already exported");
190 }
191
192 objTable.put(oe, target);
193 implTable.put(weakImpl, target);
194
195 if (!target.isPermanent()) {
196 incrementKeepAliveCount();
197 }
198 }
199 }
200
201 /**
202 * Remove target from object table.
203 *
204 * NOTE: This method must only be invoked while synchronized on
205 * the "tableLock" object, because it does not do so itself.
206 */
207 private static void removeTarget(Target target) {
208 // assert Thread.holdsLock(tableLock);
209
210 ObjectEndpoint oe = target.getObjectEndpoint();
211 WeakRef weakImpl = target.getWeakImpl();
212
213 if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) {
214 DGCImpl.dgcLog.log(Log.VERBOSE, "remove object " + oe);
215 }
216
217 objTable.remove(oe);
218 implTable.remove(weakImpl);
219
220 target.markRemoved(); // handles decrementing keep-alive count
221 }
222
223 /**
224 * Process client VM signalling reference for given ObjID: forward to
225 * correspoding Target entry. If ObjID is not found in table,
226 * no action is taken.
227 */
228 static void referenced(ObjID id, long sequenceNum, VMID vmid) {
229 synchronized (tableLock) {
230 ObjectEndpoint oe =
231 new ObjectEndpoint(id, Transport.currentTransport());
232 Target target = objTable.get(oe);
233 if (target != null) {
234 target.referenced(sequenceNum, vmid);
235 }
236 }
237 }
238
239 /**
240 * Process client VM dropping reference for given ObjID: forward to
241 * correspoding Target entry. If ObjID is not found in table,
242 * no action is taken.
243 */
244 static void unreferenced(ObjID id, long sequenceNum, VMID vmid,
245 boolean strong)
246 {
247 synchronized (tableLock) {
248 ObjectEndpoint oe =
249 new ObjectEndpoint(id, Transport.currentTransport());
250 Target target = objTable.get(oe);
251 if (target != null)
252 target.unreferenced(sequenceNum, vmid, strong);
253 }
254 }
255
256 /**
257 * Increments the "keep-alive count".
258 *
259 * The "keep-alive count" is the number of non-permanent remote objects
260 * that are either in the object table or still have calls in progress.
261 * Therefore, this method should be invoked exactly once for every
262 * non-permanent remote object exported (a remote object must be
263 * exported before it can have any calls in progress).
264 *
265 * The VM is "kept alive" while the keep-alive count is greater than
266 * zero; this is accomplished by keeping a non-daemon thread running.
267 *
268 * Because non-permanent objects are those that can be garbage
269 * collected while exported, and thus those for which the "reaper"
270 * thread operates, the reaper thread also serves as the non-daemon
271 * VM keep-alive thread; a new reaper thread is created if necessary.
272 */
273 static void incrementKeepAliveCount() {
274 synchronized (keepAliveLock) {
275 keepAliveCount++;
276
277 if (reaper == null) {
278 reaper = AccessController.doPrivileged(
279 new NewThreadAction(new Reaper(), "Reaper", false));
280 reaper.start();
281 }
282
283 /*
284 * While there are non-"permanent" objects in the object table,
285 * request a maximum latency for inspecting the entire heap
286 * from the local garbage collector, to place an upper bound
287 * on the time to discover remote objects that have become
288 * unreachable (and thus can be removed from the table).
289 */
290 if (gcLatencyRequest == null) {
291 gcLatencyRequest = GC.requestLatency(gcInterval);
292 }
293 }
294 }
295
296 /**
297 * Decrements the "keep-alive count".
298 *
299 * The "keep-alive count" is the number of non-permanent remote objects
300 * that are either in the object table or still have calls in progress.
301 * Therefore, this method should be invoked exactly once for every
302 * previously-exported non-permanent remote object that both has been
303 * removed from the object table and has no calls still in progress.
304 *
305 * If the keep-alive count is decremented to zero, then the current
306 * reaper thread is terminated to cease keeping the VM alive (and
307 * because there are no more non-permanent remote objects to reap).
308 */
309 static void decrementKeepAliveCount() {
310 synchronized (keepAliveLock) {
311 keepAliveCount--;
312
313 if (keepAliveCount == 0) {
314 if (!(reaper != null)) { throw new AssertionError(); }
315 AccessController.doPrivileged(new PrivilegedAction<Void>() {
316 public Void run() {
317 reaper.interrupt();
318 return null;
319 }
320 });
321 reaper = null;
322
323 /*
324 * If there are no longer any non-permanent objects in the
325 * object table, we are no longer concerned with the latency
326 * of local garbage collection here.
327 */
328 gcLatencyRequest.cancel();
329 gcLatencyRequest = null;
330 }
331 }
332 }
333
334 /**
335 * The Reaper thread waits for notifications that weak references in the
336 * object table have been cleared. When it receives a notification, it
337 * removes the corresponding entry from the table.
338 *
339 * Since the Reaper is created as a non-daemon thread, it also serves
340 * to keep the VM from exiting while there are objects in the table
341 * (other than permanent entries that should neither be reaped nor
342 * keep the VM alive).
343 */
344 private static class Reaper implements Runnable {
345
346 public void run() {
347 try {
348 do {
349 // wait for next cleared weak reference
350 WeakRef weakImpl = (WeakRef) reapQueue.remove();
351
352 synchronized (tableLock) {
353 Target target = implTable.get(weakImpl);
354 if (target != null) {
355 if (!target.isEmpty()) {
356 throw new Error(
357 "object with known references collected");
358 } else if (target.isPermanent()) {
359 throw new Error("permanent object collected");
360 }
361 removeTarget(target);
362 }
363 }
364 } while (!Thread.interrupted());
365 } catch (InterruptedException e) {
366 // pass away if interrupted
367 }
368 }
369 }
370 }