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| 1 | +/* | |
| 2 | + * Copyright (c) 1996, 2008, 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.PhantomReference; | |
| 28 | +import java.lang.ref.ReferenceQueue; | |
| 29 | +import java.security.AccessController; | |
| 30 | +import java.security.PrivilegedAction; | |
| 31 | +import java.util.HashMap; | |
| 32 | +import java.util.HashSet; | |
| 33 | +import java.util.Iterator; | |
| 34 | +import java.util.List; | |
| 35 | +import java.util.Map; | |
| 36 | +import java.util.Set; | |
| 37 | +import java.rmi.ConnectException; | |
| 38 | +import java.rmi.RemoteException; | |
| 39 | +import java.rmi.dgc.DGC; | |
| 40 | +import java.rmi.dgc.Lease; | |
| 41 | +import java.rmi.dgc.VMID; | |
| 42 | +import java.rmi.server.ObjID; | |
| 43 | +import sun.misc.GC; | |
| 44 | +import sun.rmi.runtime.NewThreadAction; | |
| 45 | +import sun.rmi.server.UnicastRef; | |
| 46 | +import sun.rmi.server.Util; | |
| 47 | +import sun.security.action.GetLongAction; | |
| 48 | + | |
| 49 | +/** | |
| 50 | + * DGCClient implements the client-side of the RMI distributed garbage | |
| 51 | + * collection system. | |
| 52 | + * | |
| 53 | + * The external interface to DGCClient is the "registerRefs" method. | |
| 54 | + * When a LiveRef to a remote object enters the VM, it needs to be | |
| 55 | + * registered with the DGCClient to participate in distributed garbage | |
| 56 | + * collection. | |
| 57 | + * | |
| 58 | + * When the first LiveRef to a particular remote object is registered, | |
| 59 | + * a "dirty" call is made to the server-side distributed garbage | |
| 60 | + * collector for the remote object, which returns a lease guaranteeing | |
| 61 | + * that the server-side DGC will not collect the remote object for a | |
| 62 | + * certain period of time. While LiveRef instances to remote objects | |
| 63 | + * on a particular server exist, the DGCClient periodically sends more | |
| 64 | + * "dirty" calls to renew its lease. | |
| 65 | + * | |
| 66 | + * The DGCClient tracks the local reachability of registered LiveRef | |
| 67 | + * instances (using phantom references). When the LiveRef instance | |
| 68 | + * for a particular remote object becomes garbage collected locally, | |
| 69 | + * a "clean" call is made to the server-side distributed garbage | |
| 70 | + * collector, indicating that the server no longer needs to keep the | |
| 71 | + * remote object alive for this client. | |
| 72 | + * | |
| 73 | + * @see java.rmi.dgc.DGC, sun.rmi.transport.DGCImpl | |
| 74 | + * | |
| 75 | + * @author Ann Wollrath | |
| 76 | + * @author Peter Jones | |
| 77 | + */ | |
| 78 | +final class DGCClient { | |
| 79 | + | |
| 80 | + /** next sequence number for DGC calls (access synchronized on class) */ | |
| 81 | + private static long nextSequenceNum = Long.MIN_VALUE; | |
| 82 | + | |
| 83 | + /** unique identifier for this VM as a client of DGC */ | |
| 84 | + private static VMID vmid = new VMID(); | |
| 85 | + | |
| 86 | + /** lease duration to request (usually ignored by server) */ | |
| 87 | + private static final long leaseValue = // default 10 minutes | |
| 88 | + AccessController.doPrivileged( | |
| 89 | + new GetLongAction("java.rmi.dgc.leaseValue", | |
| 90 | + 600000)).longValue(); | |
| 91 | + | |
| 92 | + /** maximum interval between retries of failed clean calls */ | |
| 93 | + private static final long cleanInterval = // default 3 minutes | |
| 94 | + AccessController.doPrivileged( | |
| 95 | + new GetLongAction("sun.rmi.dgc.cleanInterval", | |
| 96 | + 180000)).longValue(); | |
| 97 | + | |
| 98 | + /** maximum interval between complete garbage collections of local heap */ | |
| 99 | + private static final long gcInterval = // default 1 hour | |
| 100 | + AccessController.doPrivileged( | |
| 101 | + new GetLongAction("sun.rmi.dgc.client.gcInterval", | |
| 102 | + 3600000)).longValue(); | |
| 103 | + | |
| 104 | + /** minimum retry count for dirty calls that fail */ | |
| 105 | + private static final int dirtyFailureRetries = 5; | |
| 106 | + | |
| 107 | + /** retry count for clean calls that fail with ConnectException */ | |
| 108 | + private static final int cleanFailureRetries = 5; | |
| 109 | + | |
| 110 | + /** constant empty ObjID array for lease renewal optimization */ | |
| 111 | + private static final ObjID[] emptyObjIDArray = new ObjID[0]; | |
| 112 | + | |
| 113 | + /** ObjID for server-side DGC object */ | |
| 114 | + private static final ObjID dgcID = new ObjID(ObjID.DGC_ID); | |
| 115 | + | |
| 116 | + /* | |
| 117 | + * Disallow anyone from creating one of these. | |
| 118 | + */ | |
| 119 | + private DGCClient() {} | |
| 120 | + | |
| 121 | + /** | |
| 122 | + * Register the LiveRef instances in the supplied list to participate | |
| 123 | + * in distributed garbage collection. | |
| 124 | + * | |
| 125 | + * All of the LiveRefs in the list must be for remote objects at the | |
| 126 | + * given endpoint. | |
| 127 | + */ | |
| 128 | + static void registerRefs(Endpoint ep, List refs) { | |
| 129 | + /* | |
| 130 | + * Look up the given endpoint and register the refs with it. | |
| 131 | + * The retrieved entry may get removed from the global endpoint | |
| 132 | + * table before EndpointEntry.registerRefs() is able to acquire | |
| 133 | + * its lock; in this event, it returns false, and we loop and | |
| 134 | + * try again. | |
| 135 | + */ | |
| 136 | + EndpointEntry epEntry; | |
| 137 | + do { | |
| 138 | + epEntry = EndpointEntry.lookup(ep); | |
| 139 | + } while (!epEntry.registerRefs(refs)); | |
| 140 | + } | |
| 141 | + | |
| 142 | + /** | |
| 143 | + * Get the next sequence number to be used for a dirty or clean | |
| 144 | + * operation from this VM. This method should only be called while | |
| 145 | + * synchronized on the EndpointEntry whose data structures the | |
| 146 | + * operation affects. | |
| 147 | + */ | |
| 148 | + private static synchronized long getNextSequenceNum() { | |
| 149 | + return nextSequenceNum++; | |
| 150 | + } | |
| 151 | + | |
| 152 | + /** | |
| 153 | + * Given the length of a lease and the time that it was granted, | |
| 154 | + * compute the absolute time at which it should be renewed, giving | |
| 155 | + * room for reasonable computational and communication delays. | |
| 156 | + */ | |
| 157 | + private static long computeRenewTime(long grantTime, long duration) { | |
| 158 | + /* | |
| 159 | + * REMIND: This algorithm should be more sophisticated, waiting | |
| 160 | + * a longer fraction of the lease duration for longer leases. | |
| 161 | + */ | |
| 162 | + return grantTime + (duration / 2); | |
| 163 | + } | |
| 164 | + | |
| 165 | + /** | |
| 166 | + * EndpointEntry encapsulates the client-side DGC information specific | |
| 167 | + * to a particular Endpoint. Of most significance is the table that | |
| 168 | + * maps LiveRef value to RefEntry objects and the renew/clean thread | |
| 169 | + * that handles asynchronous client-side DGC operations. | |
| 170 | + */ | |
| 171 | + private static class EndpointEntry { | |
| 172 | + | |
| 173 | + /** the endpoint that this entry is for */ | |
| 174 | + private Endpoint endpoint; | |
| 175 | + /** synthesized reference to the remote server-side DGC */ | |
| 176 | + private DGC dgc; | |
| 177 | + | |
| 178 | + /** table of refs held for endpoint: maps LiveRef to RefEntry */ | |
| 179 | + private Map refTable = new HashMap(5); | |
| 180 | + /** set of RefEntry instances from last (failed) dirty call */ | |
| 181 | + private Set invalidRefs = new HashSet(5); | |
| 182 | + | |
| 183 | + /** true if this entry has been removed from the global table */ | |
| 184 | + private boolean removed = false; | |
| 185 | + | |
| 186 | + /** absolute time to renew current lease to this endpoint */ | |
| 187 | + private long renewTime = Long.MAX_VALUE; | |
| 188 | + /** absolute time current lease to this endpoint will expire */ | |
| 189 | + private long expirationTime = Long.MIN_VALUE; | |
| 190 | + /** count of recent dirty calls that have failed */ | |
| 191 | + private int dirtyFailures = 0; | |
| 192 | + /** absolute time of first recent failed dirty call */ | |
| 193 | + private long dirtyFailureStartTime; | |
| 194 | + /** (average) elapsed time for recent failed dirty calls */ | |
| 195 | + private long dirtyFailureDuration; | |
| 196 | + | |
| 197 | + /** renew/clean thread for handling lease renewals and clean calls */ | |
| 198 | + private Thread renewCleanThread; | |
| 199 | + /** true if renew/clean thread may be interrupted */ | |
| 200 | + private boolean interruptible = false; | |
| 201 | + | |
| 202 | + /** reference queue for phantom references */ | |
| 203 | + private ReferenceQueue refQueue = new ReferenceQueue(); | |
| 204 | + /** set of clean calls that need to be made */ | |
| 205 | + private Set pendingCleans = new HashSet(5); | |
| 206 | + | |
| 207 | + /** global endpoint table: maps Endpoint to EndpointEntry */ | |
| 208 | + private static Map endpointTable = new HashMap(5); | |
| 209 | + /** handle for GC latency request (for future cancellation) */ | |
| 210 | + private static GC.LatencyRequest gcLatencyRequest = null; | |
| 211 | + | |
| 212 | + /** | |
| 213 | + * Look up the EndpointEntry for the given Endpoint. An entry is | |
| 214 | + * created if one does not already exist. | |
| 215 | + */ | |
| 216 | + public static EndpointEntry lookup(Endpoint ep) { | |
| 217 | + synchronized (endpointTable) { | |
| 218 | + EndpointEntry entry = (EndpointEntry) endpointTable.get(ep); | |
| 219 | + if (entry == null) { | |
| 220 | + entry = new EndpointEntry(ep); | |
| 221 | + endpointTable.put(ep, entry); | |
| 222 | + /* | |
| 223 | + * While we are tracking live remote references registered | |
| 224 | + * in this VM, request a maximum latency for inspecting the | |
| 225 | + * entire heap from the local garbage collector, to place | |
| 226 | + * an upper bound on the time to discover remote references | |
| 227 | + * that have become unreachable (see bugid 4171278). | |
| 228 | + */ | |
| 229 | + if (gcLatencyRequest == null) { | |
| 230 | + gcLatencyRequest = GC.requestLatency(gcInterval); | |
| 231 | + } | |
| 232 | + } | |
| 233 | + return entry; | |
| 234 | + } | |
| 235 | + } | |
| 236 | + | |
| 237 | + private EndpointEntry(final Endpoint endpoint) { | |
| 238 | + this.endpoint = endpoint; | |
| 239 | + try { | |
| 240 | + LiveRef dgcRef = new LiveRef(dgcID, endpoint, false); | |
| 241 | + dgc = (DGC) Util.createProxy(DGCImpl.class, | |
| 242 | + new UnicastRef(dgcRef), true); | |
| 243 | + } catch (RemoteException e) { | |
| 244 | + throw new Error("internal error creating DGC stub"); | |
| 245 | + } | |
| 246 | + renewCleanThread = AccessController.doPrivileged( | |
| 247 | + new NewThreadAction(new RenewCleanThread(), | |
| 248 | + "RenewClean-" + endpoint, true)); | |
| 249 | + renewCleanThread.start(); | |
| 250 | + } | |
| 251 | + | |
| 252 | + /** | |
| 253 | + * Register the LiveRef instances in the supplied list to participate | |
| 254 | + * in distributed garbage collection. | |
| 255 | + * | |
| 256 | + * This method returns false if this entry was removed from the | |
| 257 | + * global endpoint table (because it was empty) before these refs | |
| 258 | + * could be registered. In that case, a new EndpointEntry needs | |
| 259 | + * to be looked up. | |
| 260 | + * | |
| 261 | + * This method must NOT be called while synchronized on this entry. | |
| 262 | + */ | |
| 263 | + public boolean registerRefs(List refs) { | |
| 264 | + assert !Thread.holdsLock(this); | |
| 265 | + | |
| 266 | + Set refsToDirty = null; // entries for refs needing dirty | |
| 267 | + long sequenceNum; // sequence number for dirty call | |
| 268 | + | |
| 269 | + synchronized (this) { | |
| 270 | + if (removed) { | |
| 271 | + return false; | |
| 272 | + } | |
| 273 | + | |
| 274 | + Iterator iter = refs.iterator(); | |
| 275 | + while (iter.hasNext()) { | |
| 276 | + LiveRef ref = (LiveRef) iter.next(); | |
| 277 | + assert ref.getEndpoint().equals(endpoint); | |
| 278 | + | |
| 279 | + RefEntry refEntry = (RefEntry) refTable.get(ref); | |
| 280 | + if (refEntry == null) { | |
| 281 | + LiveRef refClone = (LiveRef) ref.clone(); | |
| 282 | + refEntry = new RefEntry(refClone); | |
| 283 | + refTable.put(refClone, refEntry); | |
| 284 | + if (refsToDirty == null) { | |
| 285 | + refsToDirty = new HashSet(5); | |
| 286 | + } | |
| 287 | + refsToDirty.add(refEntry); | |
| 288 | + } | |
| 289 | + | |
| 290 | + refEntry.addInstanceToRefSet(ref); | |
| 291 | + } | |
| 292 | + | |
| 293 | + if (refsToDirty == null) { | |
| 294 | + return true; | |
| 295 | + } | |
| 296 | + | |
| 297 | + refsToDirty.addAll(invalidRefs); | |
| 298 | + invalidRefs.clear(); | |
| 299 | + | |
| 300 | + sequenceNum = getNextSequenceNum(); | |
| 301 | + } | |
| 302 | + | |
| 303 | + makeDirtyCall(refsToDirty, sequenceNum); | |
| 304 | + return true; | |
| 305 | + } | |
| 306 | + | |
| 307 | + /** | |
| 308 | + * Remove the given RefEntry from the ref table. If that makes | |
| 309 | + * the ref table empty, remove this entry from the global endpoint | |
| 310 | + * table. | |
| 311 | + * | |
| 312 | + * This method must ONLY be called while synchronized on this entry. | |
| 313 | + */ | |
| 314 | + private void removeRefEntry(RefEntry refEntry) { | |
| 315 | + assert Thread.holdsLock(this); | |
| 316 | + assert !removed; | |
| 317 | + assert refTable.containsKey(refEntry.getRef()); | |
| 318 | + | |
| 319 | + refTable.remove(refEntry.getRef()); | |
| 320 | + invalidRefs.remove(refEntry); | |
| 321 | + if (refTable.isEmpty()) { | |
| 322 | + synchronized (endpointTable) { | |
| 323 | + endpointTable.remove(endpoint); | |
| 324 | + Transport transport = endpoint.getOutboundTransport(); | |
| 325 | + transport.free(endpoint); | |
| 326 | + /* | |
| 327 | + * If there are no longer any live remote references | |
| 328 | + * registered, we are no longer concerned with the | |
| 329 | + * latency of local garbage collection here. | |
| 330 | + */ | |
| 331 | + if (endpointTable.isEmpty()) { | |
| 332 | + assert gcLatencyRequest != null; | |
| 333 | + gcLatencyRequest.cancel(); | |
| 334 | + gcLatencyRequest = null; | |
| 335 | + } | |
| 336 | + removed = true; | |
| 337 | + } | |
| 338 | + } | |
| 339 | + } | |
| 340 | + | |
| 341 | + /** | |
| 342 | + * Make a DGC dirty call to this entry's endpoint, for the ObjIDs | |
| 343 | + * corresponding to the given set of refs and with the given | |
| 344 | + * sequence number. | |
| 345 | + * | |
| 346 | + * This method must NOT be called while synchronized on this entry. | |
| 347 | + */ | |
| 348 | + private void makeDirtyCall(Set refEntries, long sequenceNum) { | |
| 349 | + assert !Thread.holdsLock(this); | |
| 350 | + | |
| 351 | + ObjID[] ids; | |
| 352 | + if (refEntries != null) { | |
| 353 | + ids = createObjIDArray(refEntries); | |
| 354 | + } else { | |
| 355 | + ids = emptyObjIDArray; | |
| 356 | + } | |
| 357 | + | |
| 358 | + long startTime = System.currentTimeMillis(); | |
| 359 | + try { | |
| 360 | + Lease lease = | |
| 361 | + dgc.dirty(ids, sequenceNum, new Lease(vmid, leaseValue)); | |
| 362 | + long duration = lease.getValue(); | |
| 363 | + | |
| 364 | + long newRenewTime = computeRenewTime(startTime, duration); | |
| 365 | + long newExpirationTime = startTime + duration; | |
| 366 | + | |
| 367 | + synchronized (this) { | |
| 368 | + dirtyFailures = 0; | |
| 369 | + setRenewTime(newRenewTime); | |
| 370 | + expirationTime = newExpirationTime; | |
| 371 | + } | |
| 372 | + | |
| 373 | + } catch (Exception e) { | |
| 374 | + long endTime = System.currentTimeMillis(); | |
| 375 | + | |
| 376 | + synchronized (this) { | |
| 377 | + dirtyFailures++; | |
| 378 | + | |
| 379 | + if (dirtyFailures == 1) { | |
| 380 | + /* | |
| 381 | + * If this was the first recent failed dirty call, | |
| 382 | + * reschedule another one immediately, in case there | |
| 383 | + * was just a transient network problem, and remember | |
| 384 | + * the start time and duration of this attempt for | |
| 385 | + * future calculations of the delays between retries. | |
| 386 | + */ | |
| 387 | + dirtyFailureStartTime = startTime; | |
| 388 | + dirtyFailureDuration = endTime - startTime; | |
| 389 | + setRenewTime(endTime); | |
| 390 | + } else { | |
| 391 | + /* | |
| 392 | + * For each successive failed dirty call, wait for a | |
| 393 | + * (binary) exponentially increasing delay before | |
| 394 | + * retrying, to avoid network congestion. | |
| 395 | + */ | |
| 396 | + int n = dirtyFailures - 2; | |
| 397 | + if (n == 0) { | |
| 398 | + /* | |
| 399 | + * Calculate the initial retry delay from the | |
| 400 | + * average time elapsed for each of the first | |
| 401 | + * two failed dirty calls. The result must be | |
| 402 | + * at least 1000ms, to prevent a tight loop. | |
| 403 | + */ | |
| 404 | + dirtyFailureDuration = | |
| 405 | + Math.max((dirtyFailureDuration + | |
| 406 | + (endTime - startTime)) >> 1, 1000); | |
| 407 | + } | |
| 408 | + long newRenewTime = | |
| 409 | + endTime + (dirtyFailureDuration << n); | |
| 410 | + | |
| 411 | + /* | |
| 412 | + * Continue if the last known held lease has not | |
| 413 | + * expired, or else at least a fixed number of times, | |
| 414 | + * or at least until we've tried for a fixed amount | |
| 415 | + * of time (the default lease value we request). | |
| 416 | + */ | |
| 417 | + if (newRenewTime < expirationTime || | |
| 418 | + dirtyFailures < dirtyFailureRetries || | |
| 419 | + newRenewTime < dirtyFailureStartTime + leaseValue) | |
| 420 | + { | |
| 421 | + setRenewTime(newRenewTime); | |
| 422 | + } else { | |
| 423 | + /* | |
| 424 | + * Give up: postpone lease renewals until next | |
| 425 | + * ref is registered for this endpoint. | |
| 426 | + */ | |
| 427 | + setRenewTime(Long.MAX_VALUE); | |
| 428 | + } | |
| 429 | + } | |
| 430 | + | |
| 431 | + if (refEntries != null) { | |
| 432 | + /* | |
| 433 | + * Add all of these refs to the set of refs for this | |
| 434 | + * endpoint that may be invalid (this VM may not be in | |
| 435 | + * the server's referenced set), so that we will | |
| 436 | + * attempt to explicitly dirty them again in the | |
| 437 | + * future. | |
| 438 | + */ | |
| 439 | + invalidRefs.addAll(refEntries); | |
| 440 | + | |
| 441 | + /* | |
| 442 | + * Record that a dirty call has failed for all of these | |
| 443 | + * refs, so that clean calls for them in the future | |
| 444 | + * will be strong. | |
| 445 | + */ | |
| 446 | + Iterator iter = refEntries.iterator(); | |
| 447 | + while (iter.hasNext()) { | |
| 448 | + RefEntry refEntry = (RefEntry) iter.next(); | |
| 449 | + refEntry.markDirtyFailed(); | |
| 450 | + } | |
| 451 | + } | |
| 452 | + | |
| 453 | + /* | |
| 454 | + * If the last known held lease will have expired before | |
| 455 | + * the next renewal, all refs might be invalid. | |
| 456 | + */ | |
| 457 | + if (renewTime >= expirationTime) { | |
| 458 | + invalidRefs.addAll(refTable.values()); | |
| 459 | + } | |
| 460 | + } | |
| 461 | + } | |
| 462 | + } | |
| 463 | + | |
| 464 | + /** | |
| 465 | + * Set the absolute time at which the lease for this entry should | |
| 466 | + * be renewed. | |
| 467 | + * | |
| 468 | + * This method must ONLY be called while synchronized on this entry. | |
| 469 | + */ | |
| 470 | + private void setRenewTime(long newRenewTime) { | |
| 471 | + assert Thread.holdsLock(this); | |
| 472 | + | |
| 473 | + if (newRenewTime < renewTime) { | |
| 474 | + renewTime = newRenewTime; | |
| 475 | + if (interruptible) { | |
| 476 | + AccessController.doPrivileged( | |
| 477 | + new PrivilegedAction<Void>() { | |
| 478 | + public Void run() { | |
| 479 | + renewCleanThread.interrupt(); | |
| 480 | + return null; | |
| 481 | + } | |
| 482 | + }); | |
| 483 | + } | |
| 484 | + } else { | |
| 485 | + renewTime = newRenewTime; | |
| 486 | + } | |
| 487 | + } | |
| 488 | + | |
| 489 | + /** | |
| 490 | + * RenewCleanThread handles the asynchronous client-side DGC activity | |
| 491 | + * for this entry: renewing the leases and making clean calls. | |
| 492 | + */ | |
| 493 | + private class RenewCleanThread implements Runnable { | |
| 494 | + | |
| 495 | + public void run() { | |
| 496 | + do { | |
| 497 | + long timeToWait; | |
| 498 | + RefEntry.PhantomLiveRef phantom = null; | |
| 499 | + boolean needRenewal = false; | |
| 500 | + Set refsToDirty = null; | |
| 501 | + long sequenceNum = Long.MIN_VALUE; | |
| 502 | + | |
| 503 | + synchronized (EndpointEntry.this) { | |
| 504 | + /* | |
| 505 | + * Calculate time to block (waiting for phantom | |
| 506 | + * reference notifications). It is the time until the | |
| 507 | + * lease renewal should be done, bounded on the low | |
| 508 | + * end by 1 ms so that the reference queue will always | |
| 509 | + * get processed, and if there are pending clean | |
| 510 | + * requests (remaining because some clean calls | |
| 511 | + * failed), bounded on the high end by the maximum | |
| 512 | + * clean call retry interval. | |
| 513 | + */ | |
| 514 | + long timeUntilRenew = | |
| 515 | + renewTime - System.currentTimeMillis(); | |
| 516 | + timeToWait = Math.max(timeUntilRenew, 1); | |
| 517 | + if (!pendingCleans.isEmpty()) { | |
| 518 | + timeToWait = Math.min(timeToWait, cleanInterval); | |
| 519 | + } | |
| 520 | + | |
| 521 | + /* | |
| 522 | + * Set flag indicating that it is OK to interrupt this | |
| 523 | + * thread now, such as if a earlier lease renewal time | |
| 524 | + * is set, because we are only going to be blocking | |
| 525 | + * and can deal with interrupts. | |
| 526 | + */ | |
| 527 | + interruptible = true; | |
| 528 | + } | |
| 529 | + | |
| 530 | + try { | |
| 531 | + /* | |
| 532 | + * Wait for the duration calculated above for any of | |
| 533 | + * our phantom references to be enqueued. | |
| 534 | + */ | |
| 535 | + phantom = (RefEntry.PhantomLiveRef) | |
| 536 | + refQueue.remove(timeToWait); | |
| 537 | + } catch (InterruptedException e) { | |
| 538 | + } | |
| 539 | + | |
| 540 | + synchronized (EndpointEntry.this) { | |
| 541 | + /* | |
| 542 | + * Set flag indicating that it is NOT OK to interrupt | |
| 543 | + * this thread now, because we may be undertaking I/O | |
| 544 | + * operations that should not be interrupted (and we | |
| 545 | + * will not be blocking arbitrarily). | |
| 546 | + */ | |
| 547 | + interruptible = false; | |
| 548 | + Thread.interrupted(); // clear interrupted state | |
| 549 | + | |
| 550 | + /* | |
| 551 | + * If there was a phantom reference enqueued, process | |
| 552 | + * it and all the rest on the queue, generating | |
| 553 | + * clean requests as necessary. | |
| 554 | + */ | |
| 555 | + if (phantom != null) { | |
| 556 | + processPhantomRefs(phantom); | |
| 557 | + } | |
| 558 | + | |
| 559 | + /* | |
| 560 | + * Check if it is time to renew this entry's lease. | |
| 561 | + */ | |
| 562 | + long currentTime = System.currentTimeMillis(); | |
| 563 | + if (currentTime > renewTime) { | |
| 564 | + needRenewal = true; | |
| 565 | + if (!invalidRefs.isEmpty()) { | |
| 566 | + refsToDirty = invalidRefs; | |
| 567 | + invalidRefs = new HashSet(5); | |
| 568 | + } | |
| 569 | + sequenceNum = getNextSequenceNum(); | |
| 570 | + } | |
| 571 | + } | |
| 572 | + | |
| 573 | + if (needRenewal) { | |
| 574 | + makeDirtyCall(refsToDirty, sequenceNum); | |
| 575 | + } | |
| 576 | + | |
| 577 | + if (!pendingCleans.isEmpty()) { | |
| 578 | + makeCleanCalls(); | |
| 579 | + } | |
| 580 | + } while (!removed || !pendingCleans.isEmpty()); | |
| 581 | + } | |
| 582 | + } | |
| 583 | + | |
| 584 | + /** | |
| 585 | + * Process the notification of the given phantom reference and any | |
| 586 | + * others that are on this entry's reference queue. Each phantom | |
| 587 | + * reference is removed from its RefEntry's ref set. All ref | |
| 588 | + * entries that have no more registered instances are collected | |
| 589 | + * into up to two batched clean call requests: one for refs | |
| 590 | + * requiring a "strong" clean call, and one for the rest. | |
| 591 | + * | |
| 592 | + * This method must ONLY be called while synchronized on this entry. | |
| 593 | + */ | |
| 594 | + private void processPhantomRefs(RefEntry.PhantomLiveRef phantom) { | |
| 595 | + assert Thread.holdsLock(this); | |
| 596 | + | |
| 597 | + Set strongCleans = null; | |
| 598 | + Set normalCleans = null; | |
| 599 | + | |
| 600 | + do { | |
| 601 | + RefEntry refEntry = phantom.getRefEntry(); | |
| 602 | + refEntry.removeInstanceFromRefSet(phantom); | |
| 603 | + if (refEntry.isRefSetEmpty()) { | |
| 604 | + if (refEntry.hasDirtyFailed()) { | |
| 605 | + if (strongCleans == null) { | |
| 606 | + strongCleans = new HashSet(5); | |
| 607 | + } | |
| 608 | + strongCleans.add(refEntry); | |
| 609 | + } else { | |
| 610 | + if (normalCleans == null) { | |
| 611 | + normalCleans = new HashSet(5); | |
| 612 | + } | |
| 613 | + normalCleans.add(refEntry); | |
| 614 | + } | |
| 615 | + removeRefEntry(refEntry); | |
| 616 | + } | |
| 617 | + } while ((phantom = | |
| 618 | + (RefEntry.PhantomLiveRef) refQueue.poll()) != null); | |
| 619 | + | |
| 620 | + if (strongCleans != null) { | |
| 621 | + pendingCleans.add( | |
| 622 | + new CleanRequest(createObjIDArray(strongCleans), | |
| 623 | + getNextSequenceNum(), true)); | |
| 624 | + } | |
| 625 | + if (normalCleans != null) { | |
| 626 | + pendingCleans.add( | |
| 627 | + new CleanRequest(createObjIDArray(normalCleans), | |
| 628 | + getNextSequenceNum(), false)); | |
| 629 | + } | |
| 630 | + } | |
| 631 | + | |
| 632 | + /** | |
| 633 | + * CleanRequest holds the data for the parameters of a clean call | |
| 634 | + * that needs to be made. | |
| 635 | + */ | |
| 636 | + private static class CleanRequest { | |
| 637 | + | |
| 638 | + final ObjID[] objIDs; | |
| 639 | + final long sequenceNum; | |
| 640 | + final boolean strong; | |
| 641 | + | |
| 642 | + /** how many times this request has failed */ | |
| 643 | + int failures = 0; | |
| 644 | + | |
| 645 | + CleanRequest(ObjID[] objIDs, long sequenceNum, boolean strong) { | |
| 646 | + this.objIDs = objIDs; | |
| 647 | + this.sequenceNum = sequenceNum; | |
| 648 | + this.strong = strong; | |
| 649 | + } | |
| 650 | + } | |
| 651 | + | |
| 652 | + /** | |
| 653 | + * Make all of the clean calls described by the clean requests in | |
| 654 | + * this entry's set of "pending cleans". Clean requests for clean | |
| 655 | + * calls that succeed are removed from the "pending cleans" set. | |
| 656 | + * | |
| 657 | + * This method must NOT be called while synchronized on this entry. | |
| 658 | + */ | |
| 659 | + private void makeCleanCalls() { | |
| 660 | + assert !Thread.holdsLock(this); | |
| 661 | + | |
| 662 | + Iterator iter = pendingCleans.iterator(); | |
| 663 | + while (iter.hasNext()) { | |
| 664 | + CleanRequest request = (CleanRequest) iter.next(); | |
| 665 | + try { | |
| 666 | + dgc.clean(request.objIDs, request.sequenceNum, vmid, | |
| 667 | + request.strong); | |
| 668 | + iter.remove(); | |
| 669 | + } catch (Exception e) { | |
| 670 | + /* | |
| 671 | + * Many types of exceptions here could have been | |
| 672 | + * caused by a transient failure, so try again a | |
| 673 | + * few times, but not forever. | |
| 674 | + */ | |
| 675 | + if (++request.failures >= cleanFailureRetries) { | |
| 676 | + iter.remove(); | |
| 677 | + } | |
| 678 | + } | |
| 679 | + } | |
| 680 | + } | |
| 681 | + | |
| 682 | + /** | |
| 683 | + * Create an array of ObjIDs (needed for the DGC remote calls) | |
| 684 | + * from the ids in the given set of refs. | |
| 685 | + */ | |
| 686 | + private static ObjID[] createObjIDArray(Set refEntries) { | |
| 687 | + ObjID[] ids = new ObjID[refEntries.size()]; | |
| 688 | + Iterator iter = refEntries.iterator(); | |
| 689 | + for (int i = 0; i < ids.length; i++) { | |
| 690 | + ids[i] = ((RefEntry) iter.next()).getRef().getObjID(); | |
| 691 | + } | |
| 692 | + return ids; | |
| 693 | + } | |
| 694 | + | |
| 695 | + /** | |
| 696 | + * RefEntry encapsulates the client-side DGC information specific | |
| 697 | + * to a particular LiveRef value. In particular, it contains a | |
| 698 | + * set of phantom references to all of the instances of the LiveRef | |
| 699 | + * value registered in the system (but not garbage collected | |
| 700 | + * locally). | |
| 701 | + */ | |
| 702 | + private class RefEntry { | |
| 703 | + | |
| 704 | + /** LiveRef value for this entry (not a registered instance) */ | |
| 705 | + private LiveRef ref; | |
| 706 | + /** set of phantom references to registered instances */ | |
| 707 | + private Set refSet = new HashSet(5); | |
| 708 | + /** true if a dirty call containing this ref has failed */ | |
| 709 | + private boolean dirtyFailed = false; | |
| 710 | + | |
| 711 | + public RefEntry(LiveRef ref) { | |
| 712 | + this.ref = ref; | |
| 713 | + } | |
| 714 | + | |
| 715 | + /** | |
| 716 | + * Return the LiveRef value for this entry (not a registered | |
| 717 | + * instance). | |
| 718 | + */ | |
| 719 | + public LiveRef getRef() { | |
| 720 | + return ref; | |
| 721 | + } | |
| 722 | + | |
| 723 | + /** | |
| 724 | + * Add a LiveRef to the set of registered instances for this entry. | |
| 725 | + * | |
| 726 | + * This method must ONLY be invoked while synchronized on this | |
| 727 | + * RefEntry's EndpointEntry. | |
| 728 | + */ | |
| 729 | + public void addInstanceToRefSet(LiveRef ref) { | |
| 730 | + assert Thread.holdsLock(EndpointEntry.this); | |
| 731 | + assert ref.equals(this.ref); | |
| 732 | + | |
| 733 | + /* | |
| 734 | + * Only keep a phantom reference to the registered instance, | |
| 735 | + * so that it can be garbage collected normally (and we can be | |
| 736 | + * notified when that happens). | |
| 737 | + */ | |
| 738 | + refSet.add(new PhantomLiveRef(ref)); | |
| 739 | + } | |
| 740 | + | |
| 741 | + /** | |
| 742 | + * Remove a PhantomLiveRef from the set of registered instances. | |
| 743 | + * | |
| 744 | + * This method must ONLY be invoked while synchronized on this | |
| 745 | + * RefEntry's EndpointEntry. | |
| 746 | + */ | |
| 747 | + public void removeInstanceFromRefSet(PhantomLiveRef phantom) { | |
| 748 | + assert Thread.holdsLock(EndpointEntry.this); | |
| 749 | + assert refSet.contains(phantom); | |
| 750 | + refSet.remove(phantom); | |
| 751 | + } | |
| 752 | + | |
| 753 | + /** | |
| 754 | + * Return true if there are no registered LiveRef instances for | |
| 755 | + * this entry still reachable in this VM. | |
| 756 | + * | |
| 757 | + * This method must ONLY be invoked while synchronized on this | |
| 758 | + * RefEntry's EndpointEntry. | |
| 759 | + */ | |
| 760 | + public boolean isRefSetEmpty() { | |
| 761 | + assert Thread.holdsLock(EndpointEntry.this); | |
| 762 | + return refSet.size() == 0; | |
| 763 | + } | |
| 764 | + | |
| 765 | + /** | |
| 766 | + * Record that a dirty call that explicitly contained this | |
| 767 | + * entry's ref has failed. | |
| 768 | + * | |
| 769 | + * This method must ONLY be invoked while synchronized on this | |
| 770 | + * RefEntry's EndpointEntry. | |
| 771 | + */ | |
| 772 | + public void markDirtyFailed() { | |
| 773 | + assert Thread.holdsLock(EndpointEntry.this); | |
| 774 | + dirtyFailed = true; | |
| 775 | + } | |
| 776 | + | |
| 777 | + /** | |
| 778 | + * Return true if a dirty call that explicitly contained this | |
| 779 | + * entry's ref has failed (and therefore a clean call for this | |
| 780 | + * ref needs to be marked "strong"). | |
| 781 | + * | |
| 782 | + * This method must ONLY be invoked while synchronized on this | |
| 783 | + * RefEntry's EndpointEntry. | |
| 784 | + */ | |
| 785 | + public boolean hasDirtyFailed() { | |
| 786 | + assert Thread.holdsLock(EndpointEntry.this); | |
| 787 | + return dirtyFailed; | |
| 788 | + } | |
| 789 | + | |
| 790 | + /** | |
| 791 | + * PhantomLiveRef is a PhantomReference to a LiveRef instance, | |
| 792 | + * used to detect when the LiveRef becomes permanently | |
| 793 | + * unreachable in this VM. | |
| 794 | + */ | |
| 795 | + private class PhantomLiveRef extends PhantomReference { | |
| 796 | + | |
| 797 | + public PhantomLiveRef(LiveRef ref) { | |
| 798 | + super(ref, EndpointEntry.this.refQueue); | |
| 799 | + } | |
| 800 | + | |
| 801 | + public RefEntry getRefEntry() { | |
| 802 | + return RefEntry.this; | |
| 803 | + } | |
| 804 | + } | |
| 805 | + } | |
| 806 | + } | |
| 807 | +} | |