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| 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 | + synchronized (tableLock) { | |
| 179 | + /** | |
| 180 | + * Do nothing if impl has already been collected (see 6597112). Check while | |
| 181 | + * holding tableLock to ensure that Reaper cannot process weakImpl in between | |
| 182 | + * null check and put/increment effects. | |
| 183 | + */ | |
| 184 | + if (target.getImpl() != null) { | |
| 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 | + /** | |
| 203 | + * Remove target from object table. | |
| 204 | + * | |
| 205 | + * NOTE: This method must only be invoked while synchronized on | |
| 206 | + * the "tableLock" object, because it does not do so itself. | |
| 207 | + */ | |
| 208 | + private static void removeTarget(Target target) { | |
| 209 | + // assert Thread.holdsLock(tableLock); | |
| 210 | + | |
| 211 | + ObjectEndpoint oe = target.getObjectEndpoint(); | |
| 212 | + WeakRef weakImpl = target.getWeakImpl(); | |
| 213 | + | |
| 214 | + if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) { | |
| 215 | + DGCImpl.dgcLog.log(Log.VERBOSE, "remove object " + oe); | |
| 216 | + } | |
| 217 | + | |
| 218 | + objTable.remove(oe); | |
| 219 | + implTable.remove(weakImpl); | |
| 220 | + | |
| 221 | + target.markRemoved(); // handles decrementing keep-alive count | |
| 222 | + } | |
| 223 | + | |
| 224 | + /** | |
| 225 | + * Process client VM signalling reference for given ObjID: forward to | |
| 226 | + * correspoding Target entry. If ObjID is not found in table, | |
| 227 | + * no action is taken. | |
| 228 | + */ | |
| 229 | + static void referenced(ObjID id, long sequenceNum, VMID vmid) { | |
| 230 | + synchronized (tableLock) { | |
| 231 | + ObjectEndpoint oe = | |
| 232 | + new ObjectEndpoint(id, Transport.currentTransport()); | |
| 233 | + Target target = objTable.get(oe); | |
| 234 | + if (target != null) { | |
| 235 | + target.referenced(sequenceNum, vmid); | |
| 236 | + } | |
| 237 | + } | |
| 238 | + } | |
| 239 | + | |
| 240 | + /** | |
| 241 | + * Process client VM dropping reference for given ObjID: forward to | |
| 242 | + * correspoding Target entry. If ObjID is not found in table, | |
| 243 | + * no action is taken. | |
| 244 | + */ | |
| 245 | + static void unreferenced(ObjID id, long sequenceNum, VMID vmid, | |
| 246 | + boolean strong) | |
| 247 | + { | |
| 248 | + synchronized (tableLock) { | |
| 249 | + ObjectEndpoint oe = | |
| 250 | + new ObjectEndpoint(id, Transport.currentTransport()); | |
| 251 | + Target target = objTable.get(oe); | |
| 252 | + if (target != null) | |
| 253 | + target.unreferenced(sequenceNum, vmid, strong); | |
| 254 | + } | |
| 255 | + } | |
| 256 | + | |
| 257 | + /** | |
| 258 | + * Increments the "keep-alive count". | |
| 259 | + * | |
| 260 | + * The "keep-alive count" is the number of non-permanent remote objects | |
| 261 | + * that are either in the object table or still have calls in progress. | |
| 262 | + * Therefore, this method should be invoked exactly once for every | |
| 263 | + * non-permanent remote object exported (a remote object must be | |
| 264 | + * exported before it can have any calls in progress). | |
| 265 | + * | |
| 266 | + * The VM is "kept alive" while the keep-alive count is greater than | |
| 267 | + * zero; this is accomplished by keeping a non-daemon thread running. | |
| 268 | + * | |
| 269 | + * Because non-permanent objects are those that can be garbage | |
| 270 | + * collected while exported, and thus those for which the "reaper" | |
| 271 | + * thread operates, the reaper thread also serves as the non-daemon | |
| 272 | + * VM keep-alive thread; a new reaper thread is created if necessary. | |
| 273 | + */ | |
| 274 | + static void incrementKeepAliveCount() { | |
| 275 | + synchronized (keepAliveLock) { | |
| 276 | + keepAliveCount++; | |
| 277 | + | |
| 278 | + if (reaper == null) { | |
| 279 | + reaper = AccessController.doPrivileged( | |
| 280 | + new NewThreadAction(new Reaper(), "Reaper", false)); | |
| 281 | + reaper.start(); | |
| 282 | + } | |
| 283 | + | |
| 284 | + /* | |
| 285 | + * While there are non-"permanent" objects in the object table, | |
| 286 | + * request a maximum latency for inspecting the entire heap | |
| 287 | + * from the local garbage collector, to place an upper bound | |
| 288 | + * on the time to discover remote objects that have become | |
| 289 | + * unreachable (and thus can be removed from the table). | |
| 290 | + */ | |
| 291 | + if (gcLatencyRequest == null) { | |
| 292 | + gcLatencyRequest = GC.requestLatency(gcInterval); | |
| 293 | + } | |
| 294 | + } | |
| 295 | + } | |
| 296 | + | |
| 297 | + /** | |
| 298 | + * Decrements the "keep-alive count". | |
| 299 | + * | |
| 300 | + * The "keep-alive count" is the number of non-permanent remote objects | |
| 301 | + * that are either in the object table or still have calls in progress. | |
| 302 | + * Therefore, this method should be invoked exactly once for every | |
| 303 | + * previously-exported non-permanent remote object that both has been | |
| 304 | + * removed from the object table and has no calls still in progress. | |
| 305 | + * | |
| 306 | + * If the keep-alive count is decremented to zero, then the current | |
| 307 | + * reaper thread is terminated to cease keeping the VM alive (and | |
| 308 | + * because there are no more non-permanent remote objects to reap). | |
| 309 | + */ | |
| 310 | + static void decrementKeepAliveCount() { | |
| 311 | + synchronized (keepAliveLock) { | |
| 312 | + keepAliveCount--; | |
| 313 | + | |
| 314 | + if (keepAliveCount == 0) { | |
| 315 | + if (!(reaper != null)) { throw new AssertionError(); } | |
| 316 | + AccessController.doPrivileged(new PrivilegedAction<Void>() { | |
| 317 | + public Void run() { | |
| 318 | + reaper.interrupt(); | |
| 319 | + return null; | |
| 320 | + } | |
| 321 | + }); | |
| 322 | + reaper = null; | |
| 323 | + | |
| 324 | + /* | |
| 325 | + * If there are no longer any non-permanent objects in the | |
| 326 | + * object table, we are no longer concerned with the latency | |
| 327 | + * of local garbage collection here. | |
| 328 | + */ | |
| 329 | + gcLatencyRequest.cancel(); | |
| 330 | + gcLatencyRequest = null; | |
| 331 | + } | |
| 332 | + } | |
| 333 | + } | |
| 334 | + | |
| 335 | + /** | |
| 336 | + * The Reaper thread waits for notifications that weak references in the | |
| 337 | + * object table have been cleared. When it receives a notification, it | |
| 338 | + * removes the corresponding entry from the table. | |
| 339 | + * | |
| 340 | + * Since the Reaper is created as a non-daemon thread, it also serves | |
| 341 | + * to keep the VM from exiting while there are objects in the table | |
| 342 | + * (other than permanent entries that should neither be reaped nor | |
| 343 | + * keep the VM alive). | |
| 344 | + */ | |
| 345 | + private static class Reaper implements Runnable { | |
| 346 | + | |
| 347 | + public void run() { | |
| 348 | + try { | |
| 349 | + do { | |
| 350 | + // wait for next cleared weak reference | |
| 351 | + WeakRef weakImpl = (WeakRef) reapQueue.remove(); | |
| 352 | + | |
| 353 | + synchronized (tableLock) { | |
| 354 | + Target target = implTable.get(weakImpl); | |
| 355 | + if (target != null) { | |
| 356 | + if (!target.isEmpty()) { | |
| 357 | + throw new Error( | |
| 358 | + "object with known references collected"); | |
| 359 | + } else if (target.isPermanent()) { | |
| 360 | + throw new Error("permanent object collected"); | |
| 361 | + } | |
| 362 | + removeTarget(target); | |
| 363 | + } | |
| 364 | + } | |
| 365 | + } while (!Thread.interrupted()); | |
| 366 | + } catch (InterruptedException e) { | |
| 367 | + // pass away if interrupted | |
| 368 | + } | |
| 369 | + } | |
| 370 | + } | |
| 371 | +} | |