1/* 2 * Copyright (c) 1996, 2015, 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 */ 25package sun.rmi.transport; 26 27import java.io.InvalidClassException; 28import java.lang.ref.PhantomReference; 29import java.lang.ref.ReferenceQueue; 30import java.net.SocketPermission; 31import java.rmi.UnmarshalException; 32import java.security.AccessController; 33import java.security.PrivilegedAction; 34import java.util.HashMap; 35import java.util.HashSet; 36import java.util.Iterator; 37import java.util.List; 38import java.util.Map; 39import java.util.Set; 40import java.rmi.ConnectException; 41import java.rmi.RemoteException; 42import java.rmi.dgc.DGC; 43import java.rmi.dgc.Lease; 44import java.rmi.dgc.VMID; 45import java.rmi.server.ObjID; 46 47import sun.rmi.runtime.Log; 48import sun.rmi.runtime.NewThreadAction; 49import sun.rmi.server.UnicastRef; 50import sun.rmi.server.Util; 51 52import java.security.AccessControlContext; 53import java.security.Permissions; 54import java.security.ProtectionDomain; 55 56/** 57 * DGCClient implements the client-side of the RMI distributed garbage 58 * collection system. 59 * 60 * The external interface to DGCClient is the "registerRefs" method. 61 * When a LiveRef to a remote object enters the VM, it needs to be 62 * registered with the DGCClient to participate in distributed garbage 63 * collection. 64 * 65 * When the first LiveRef to a particular remote object is registered, 66 * a "dirty" call is made to the server-side distributed garbage 67 * collector for the remote object, which returns a lease guaranteeing 68 * that the server-side DGC will not collect the remote object for a 69 * certain period of time. While LiveRef instances to remote objects 70 * on a particular server exist, the DGCClient periodically sends more 71 * "dirty" calls to renew its lease. 72 * 73 * The DGCClient tracks the local reachability of registered LiveRef 74 * instances (using phantom references). When the LiveRef instance 75 * for a particular remote object becomes garbage collected locally, 76 * a "clean" call is made to the server-side distributed garbage 77 * collector, indicating that the server no longer needs to keep the 78 * remote object alive for this client. 79 * 80 * @see java.rmi.dgc.DGC, sun.rmi.transport.DGCImpl 81 * 82 * @author Ann Wollrath 83 * @author Peter Jones 84 */ 85final class DGCClient { 86 87 /** next sequence number for DGC calls (access synchronized on class) */ 88 private static long nextSequenceNum = Long.MIN_VALUE; 89 90 /** unique identifier for this VM as a client of DGC */ 91 private static VMID vmid = new VMID(); 92 93 /** lease duration to request (usually ignored by server) */ 94 private static final long leaseValue = // default 10 minutes 95 AccessController.doPrivileged((PrivilegedAction<Long>) () -> 96 Long.getLong("java.rmi.dgc.leaseValue", 600000)); 97 98 /** maximum interval between retries of failed clean calls */ 99 private static final long cleanInterval = // default 3 minutes 100 AccessController.doPrivileged((PrivilegedAction<Long>) () -> 101 Long.getLong("sun.rmi.dgc.cleanInterval", 180000)); 102 103 /** maximum interval between complete garbage collections of local heap */ 104 private static final long gcInterval = // default 1 hour 105 AccessController.doPrivileged((PrivilegedAction<Long>) () -> 106 Long.getLong("sun.rmi.dgc.client.gcInterval", 3600000)); 107 108 /** minimum retry count for dirty calls that fail */ 109 private static final int dirtyFailureRetries = 5; 110 111 /** retry count for clean calls that fail with ConnectException */ 112 private static final int cleanFailureRetries = 5; 113 114 /** constant empty ObjID array for lease renewal optimization */ 115 private static final ObjID[] emptyObjIDArray = new ObjID[0]; 116 117 /** ObjID for server-side DGC object */ 118 private static final ObjID dgcID = new ObjID(ObjID.DGC_ID); 119 120 /** 121 * An AccessControlContext with only socket permissions, 122 * suitable for an RMIClientSocketFactory. 123 */ 124 private static final AccessControlContext SOCKET_ACC; 125 static { 126 Permissions perms = new Permissions(); 127 perms.add(new SocketPermission("*", "connect,resolve")); 128 ProtectionDomain[] pd = { new ProtectionDomain(null, perms) }; 129 SOCKET_ACC = new AccessControlContext(pd); 130 } 131 132 /* 133 * Disallow anyone from creating one of these. 134 */ 135 private DGCClient() {} 136 137 /** 138 * Register the LiveRef instances in the supplied list to participate 139 * in distributed garbage collection. 140 * 141 * All of the LiveRefs in the list must be for remote objects at the 142 * given endpoint. 143 */ 144 static void registerRefs(Endpoint ep, List<LiveRef> refs) { 145 /* 146 * Look up the given endpoint and register the refs with it. 147 * The retrieved entry may get removed from the global endpoint 148 * table before EndpointEntry.registerRefs() is able to acquire 149 * its lock; in this event, it returns false, and we loop and 150 * try again. 151 */ 152 EndpointEntry epEntry; 153 do { 154 epEntry = EndpointEntry.lookup(ep); 155 } while (!epEntry.registerRefs(refs)); 156 } 157 158 /** 159 * Get the next sequence number to be used for a dirty or clean 160 * operation from this VM. This method should only be called while 161 * synchronized on the EndpointEntry whose data structures the 162 * operation affects. 163 */ 164 private static synchronized long getNextSequenceNum() { 165 return nextSequenceNum++; 166 } 167 168 /** 169 * Given the length of a lease and the time that it was granted, 170 * compute the absolute time at which it should be renewed, giving 171 * room for reasonable computational and communication delays. 172 */ 173 private static long computeRenewTime(long grantTime, long duration) { 174 /* 175 * REMIND: This algorithm should be more sophisticated, waiting 176 * a longer fraction of the lease duration for longer leases. 177 */ 178 return grantTime + (duration / 2); 179 } 180 181 /** 182 * EndpointEntry encapsulates the client-side DGC information specific 183 * to a particular Endpoint. Of most significance is the table that 184 * maps LiveRef value to RefEntry objects and the renew/clean thread 185 * that handles asynchronous client-side DGC operations. 186 */ 187 private static class EndpointEntry { 188 189 /** the endpoint that this entry is for */ 190 private Endpoint endpoint; 191 /** synthesized reference to the remote server-side DGC */ 192 private DGC dgc; 193 194 /** table of refs held for endpoint: maps LiveRef to RefEntry */ 195 private Map<LiveRef, RefEntry> refTable = new HashMap<>(5); 196 /** set of RefEntry instances from last (failed) dirty call */ 197 private Set<RefEntry> invalidRefs = new HashSet<>(5); 198 199 /** true if this entry has been removed from the global table */ 200 private boolean removed = false; 201 202 /** absolute time to renew current lease to this endpoint */ 203 private long renewTime = Long.MAX_VALUE; 204 /** absolute time current lease to this endpoint will expire */ 205 private long expirationTime = Long.MIN_VALUE; 206 /** count of recent dirty calls that have failed */ 207 private int dirtyFailures = 0; 208 /** absolute time of first recent failed dirty call */ 209 private long dirtyFailureStartTime; 210 /** (average) elapsed time for recent failed dirty calls */ 211 private long dirtyFailureDuration; 212 213 /** renew/clean thread for handling lease renewals and clean calls */ 214 private Thread renewCleanThread; 215 /** true if renew/clean thread may be interrupted */ 216 private boolean interruptible = false; 217 218 /** reference queue for phantom references */ 219 private ReferenceQueue<LiveRef> refQueue = new ReferenceQueue<>(); 220 /** set of clean calls that need to be made */ 221 private Set<CleanRequest> pendingCleans = new HashSet<>(5); 222 223 /** global endpoint table: maps Endpoint to EndpointEntry */ 224 private static Map<Endpoint,EndpointEntry> endpointTable = new HashMap<>(5); 225 /** handle for GC latency request (for future cancellation) */ 226 private static GC.LatencyRequest gcLatencyRequest = null; 227 228 /** 229 * Look up the EndpointEntry for the given Endpoint. An entry is 230 * created if one does not already exist. 231 */ 232 public static EndpointEntry lookup(Endpoint ep) { 233 synchronized (endpointTable) { 234 EndpointEntry entry = endpointTable.get(ep); 235 if (entry == null) { 236 entry = new EndpointEntry(ep); 237 endpointTable.put(ep, entry); 238 /* 239 * While we are tracking live remote references registered 240 * in this VM, request a maximum latency for inspecting the 241 * entire heap from the local garbage collector, to place 242 * an upper bound on the time to discover remote references 243 * that have become unreachable (see bugid 4171278). 244 */ 245 if (gcLatencyRequest == null) { 246 gcLatencyRequest = GC.requestLatency(gcInterval); 247 } 248 } 249 return entry; 250 } 251 } 252 253 private EndpointEntry(final Endpoint endpoint) { 254 this.endpoint = endpoint; 255 try { 256 LiveRef dgcRef = new LiveRef(dgcID, endpoint, false); 257 dgc = (DGC) Util.createProxy(DGCImpl.class, 258 new UnicastRef(dgcRef), true); 259 } catch (RemoteException e) { 260 throw new Error("internal error creating DGC stub"); 261 } 262 renewCleanThread = AccessController.doPrivileged( 263 new NewThreadAction(new RenewCleanThread(), 264 "RenewClean-" + endpoint, true)); 265 renewCleanThread.start(); 266 } 267 268 /** 269 * Register the LiveRef instances in the supplied list to participate 270 * in distributed garbage collection. 271 * 272 * This method returns false if this entry was removed from the 273 * global endpoint table (because it was empty) before these refs 274 * could be registered. In that case, a new EndpointEntry needs 275 * to be looked up. 276 * 277 * This method must NOT be called while synchronized on this entry. 278 */ 279 public boolean registerRefs(List<LiveRef> refs) { 280 assert !Thread.holdsLock(this); 281 282 Set<RefEntry> refsToDirty = null; // entries for refs needing dirty 283 long sequenceNum; // sequence number for dirty call 284 285 synchronized (this) { 286 if (removed) { 287 return false; 288 } 289 290 Iterator<LiveRef> iter = refs.iterator(); 291 while (iter.hasNext()) { 292 LiveRef ref = iter.next(); 293 assert ref.getEndpoint().equals(endpoint); 294 295 RefEntry refEntry = refTable.get(ref); 296 if (refEntry == null) { 297 LiveRef refClone = (LiveRef) ref.clone(); 298 refEntry = new RefEntry(refClone); 299 refTable.put(refClone, refEntry); 300 if (refsToDirty == null) { 301 refsToDirty = new HashSet<>(5); 302 } 303 refsToDirty.add(refEntry); 304 } 305 306 refEntry.addInstanceToRefSet(ref); 307 } 308 309 if (refsToDirty == null) { 310 return true; 311 } 312 313 refsToDirty.addAll(invalidRefs); 314 invalidRefs.clear(); 315 316 sequenceNum = getNextSequenceNum(); 317 } 318 319 makeDirtyCall(refsToDirty, sequenceNum); 320 return true; 321 } 322 323 /** 324 * Remove the given RefEntry from the ref table. If that makes 325 * the ref table empty, remove this entry from the global endpoint 326 * table. 327 * 328 * This method must ONLY be called while synchronized on this entry. 329 */ 330 private void removeRefEntry(RefEntry refEntry) { 331 assert Thread.holdsLock(this); 332 assert !removed; 333 assert refTable.containsKey(refEntry.getRef()); 334 335 refTable.remove(refEntry.getRef()); 336 invalidRefs.remove(refEntry); 337 if (refTable.isEmpty()) { 338 synchronized (endpointTable) { 339 endpointTable.remove(endpoint); 340 Transport transport = endpoint.getOutboundTransport(); 341 transport.free(endpoint); 342 /* 343 * If there are no longer any live remote references 344 * registered, we are no longer concerned with the 345 * latency of local garbage collection here. 346 */ 347 if (endpointTable.isEmpty()) { 348 assert gcLatencyRequest != null; 349 gcLatencyRequest.cancel(); 350 gcLatencyRequest = null; 351 } 352 removed = true; 353 } 354 } 355 } 356 357 /** 358 * Make a DGC dirty call to this entry's endpoint, for the ObjIDs 359 * corresponding to the given set of refs and with the given 360 * sequence number. 361 * 362 * This method must NOT be called while synchronized on this entry. 363 */ 364 private void makeDirtyCall(Set<RefEntry> refEntries, long sequenceNum) { 365 assert !Thread.holdsLock(this); 366 367 ObjID[] ids; 368 if (refEntries != null) { 369 ids = createObjIDArray(refEntries); 370 } else { 371 ids = emptyObjIDArray; 372 } 373 374 long startTime = System.currentTimeMillis(); 375 try { 376 Lease lease = 377 dgc.dirty(ids, sequenceNum, new Lease(vmid, leaseValue)); 378 long duration = lease.getValue(); 379 380 long newRenewTime = computeRenewTime(startTime, duration); 381 long newExpirationTime = startTime + duration; 382 383 synchronized (this) { 384 dirtyFailures = 0; 385 setRenewTime(newRenewTime); 386 expirationTime = newExpirationTime; 387 } 388 389 } catch (Exception e) { 390 long endTime = System.currentTimeMillis(); 391 392 synchronized (this) { 393 dirtyFailures++; 394 395 if (e instanceof UnmarshalException 396 && e.getCause() instanceof InvalidClassException) { 397 DGCImpl.dgcLog.log(Log.BRIEF, "InvalidClassException exception in DGC dirty call", e); 398 return; // protocol error, do not register these refs 399 } 400 401 if (dirtyFailures == 1) { 402 /* 403 * If this was the first recent failed dirty call, 404 * reschedule another one immediately, in case there 405 * was just a transient network problem, and remember 406 * the start time and duration of this attempt for 407 * future calculations of the delays between retries. 408 */ 409 dirtyFailureStartTime = startTime; 410 dirtyFailureDuration = endTime - startTime; 411 setRenewTime(endTime); 412 } else { 413 /* 414 * For each successive failed dirty call, wait for a 415 * (binary) exponentially increasing delay before 416 * retrying, to avoid network congestion. 417 */ 418 int n = dirtyFailures - 2; 419 if (n == 0) { 420 /* 421 * Calculate the initial retry delay from the 422 * average time elapsed for each of the first 423 * two failed dirty calls. The result must be 424 * at least 1000ms, to prevent a tight loop. 425 */ 426 dirtyFailureDuration = 427 Math.max((dirtyFailureDuration + 428 (endTime - startTime)) >> 1, 1000); 429 } 430 long newRenewTime = 431 endTime + (dirtyFailureDuration << n); 432 433 /* 434 * Continue if the last known held lease has not 435 * expired, or else at least a fixed number of times, 436 * or at least until we've tried for a fixed amount 437 * of time (the default lease value we request). 438 */ 439 if (newRenewTime < expirationTime || 440 dirtyFailures < dirtyFailureRetries || 441 newRenewTime < dirtyFailureStartTime + leaseValue) 442 { 443 setRenewTime(newRenewTime); 444 } else { 445 /* 446 * Give up: postpone lease renewals until next 447 * ref is registered for this endpoint. 448 */ 449 setRenewTime(Long.MAX_VALUE); 450 } 451 } 452 453 if (refEntries != null) { 454 /* 455 * Add all of these refs to the set of refs for this 456 * endpoint that may be invalid (this VM may not be in 457 * the server's referenced set), so that we will 458 * attempt to explicitly dirty them again in the 459 * future. 460 */ 461 invalidRefs.addAll(refEntries); 462 463 /* 464 * Record that a dirty call has failed for all of these 465 * refs, so that clean calls for them in the future 466 * will be strong. 467 */ 468 Iterator<RefEntry> iter = refEntries.iterator(); 469 while (iter.hasNext()) { 470 RefEntry refEntry = iter.next(); 471 refEntry.markDirtyFailed(); 472 } 473 } 474 475 /* 476 * If the last known held lease will have expired before 477 * the next renewal, all refs might be invalid. 478 */ 479 if (renewTime >= expirationTime) { 480 invalidRefs.addAll(refTable.values()); 481 } 482 } 483 } 484 } 485 486 /** 487 * Set the absolute time at which the lease for this entry should 488 * be renewed. 489 * 490 * This method must ONLY be called while synchronized on this entry. 491 */ 492 private void setRenewTime(long newRenewTime) { 493 assert Thread.holdsLock(this); 494 495 if (newRenewTime < renewTime) { 496 renewTime = newRenewTime; 497 if (interruptible) { 498 AccessController.doPrivileged( 499 new PrivilegedAction<Void>() { 500 public Void run() { 501 renewCleanThread.interrupt(); 502 return null; 503 } 504 }); 505 } 506 } else { 507 renewTime = newRenewTime; 508 } 509 } 510 511 /** 512 * RenewCleanThread handles the asynchronous client-side DGC activity 513 * for this entry: renewing the leases and making clean calls. 514 */ 515 private class RenewCleanThread implements Runnable { 516 517 public void run() { 518 do { 519 long timeToWait; 520 RefEntry.PhantomLiveRef phantom = null; 521 boolean needRenewal = false; 522 Set<RefEntry> refsToDirty = null; 523 long sequenceNum = Long.MIN_VALUE; 524 525 synchronized (EndpointEntry.this) { 526 /* 527 * Calculate time to block (waiting for phantom 528 * reference notifications). It is the time until the 529 * lease renewal should be done, bounded on the low 530 * end by 1 ms so that the reference queue will always 531 * get processed, and if there are pending clean 532 * requests (remaining because some clean calls 533 * failed), bounded on the high end by the maximum 534 * clean call retry interval. 535 */ 536 long timeUntilRenew = 537 renewTime - System.currentTimeMillis(); 538 timeToWait = Math.max(timeUntilRenew, 1); 539 if (!pendingCleans.isEmpty()) { 540 timeToWait = Math.min(timeToWait, cleanInterval); 541 } 542 543 /* 544 * Set flag indicating that it is OK to interrupt this 545 * thread now, such as if a earlier lease renewal time 546 * is set, because we are only going to be blocking 547 * and can deal with interrupts. 548 */ 549 interruptible = true; 550 } 551 552 try { 553 /* 554 * Wait for the duration calculated above for any of 555 * our phantom references to be enqueued. 556 */ 557 phantom = (RefEntry.PhantomLiveRef) 558 refQueue.remove(timeToWait); 559 } catch (InterruptedException e) { 560 } 561 562 synchronized (EndpointEntry.this) { 563 /* 564 * Set flag indicating that it is NOT OK to interrupt 565 * this thread now, because we may be undertaking I/O 566 * operations that should not be interrupted (and we 567 * will not be blocking arbitrarily). 568 */ 569 interruptible = false; 570 Thread.interrupted(); // clear interrupted state 571 572 /* 573 * If there was a phantom reference enqueued, process 574 * it and all the rest on the queue, generating 575 * clean requests as necessary. 576 */ 577 if (phantom != null) { 578 processPhantomRefs(phantom); 579 } 580 581 /* 582 * Check if it is time to renew this entry's lease. 583 */ 584 long currentTime = System.currentTimeMillis(); 585 if (currentTime > renewTime) { 586 needRenewal = true; 587 if (!invalidRefs.isEmpty()) { 588 refsToDirty = invalidRefs; 589 invalidRefs = new HashSet<>(5); 590 } 591 sequenceNum = getNextSequenceNum(); 592 } 593 } 594 595 boolean needRenewal_ = needRenewal; 596 Set<RefEntry> refsToDirty_ = refsToDirty; 597 long sequenceNum_ = sequenceNum; 598 AccessController.doPrivileged((PrivilegedAction<Void>)() -> { 599 if (needRenewal_) { 600 makeDirtyCall(refsToDirty_, sequenceNum_); 601 } 602 603 if (!pendingCleans.isEmpty()) { 604 makeCleanCalls(); 605 } 606 return null; 607 }, SOCKET_ACC); 608 } while (!removed || !pendingCleans.isEmpty()); 609 } 610 } 611 612 /** 613 * Process the notification of the given phantom reference and any 614 * others that are on this entry's reference queue. Each phantom 615 * reference is removed from its RefEntry's ref set. All ref 616 * entries that have no more registered instances are collected 617 * into up to two batched clean call requests: one for refs 618 * requiring a "strong" clean call, and one for the rest. 619 * 620 * This method must ONLY be called while synchronized on this entry. 621 */ 622 private void processPhantomRefs(RefEntry.PhantomLiveRef phantom) { 623 assert Thread.holdsLock(this); 624 625 Set<RefEntry> strongCleans = null; 626 Set<RefEntry> normalCleans = null; 627 628 do { 629 RefEntry refEntry = phantom.getRefEntry(); 630 refEntry.removeInstanceFromRefSet(phantom); 631 if (refEntry.isRefSetEmpty()) { 632 if (refEntry.hasDirtyFailed()) { 633 if (strongCleans == null) { 634 strongCleans = new HashSet<>(5); 635 } 636 strongCleans.add(refEntry); 637 } else { 638 if (normalCleans == null) { 639 normalCleans = new HashSet<>(5); 640 } 641 normalCleans.add(refEntry); 642 } 643 removeRefEntry(refEntry); 644 } 645 } while ((phantom = 646 (RefEntry.PhantomLiveRef) refQueue.poll()) != null); 647 648 if (strongCleans != null) { 649 pendingCleans.add( 650 new CleanRequest(createObjIDArray(strongCleans), 651 getNextSequenceNum(), true)); 652 } 653 if (normalCleans != null) { 654 pendingCleans.add( 655 new CleanRequest(createObjIDArray(normalCleans), 656 getNextSequenceNum(), false)); 657 } 658 } 659 660 /** 661 * CleanRequest holds the data for the parameters of a clean call 662 * that needs to be made. 663 */ 664 private static class CleanRequest { 665 666 final ObjID[] objIDs; 667 final long sequenceNum; 668 final boolean strong; 669 670 /** how many times this request has failed */ 671 int failures = 0; 672 673 CleanRequest(ObjID[] objIDs, long sequenceNum, boolean strong) { 674 this.objIDs = objIDs; 675 this.sequenceNum = sequenceNum; 676 this.strong = strong; 677 } 678 } 679 680 /** 681 * Make all of the clean calls described by the clean requests in 682 * this entry's set of "pending cleans". Clean requests for clean 683 * calls that succeed are removed from the "pending cleans" set. 684 * 685 * This method must NOT be called while synchronized on this entry. 686 */ 687 private void makeCleanCalls() { 688 assert !Thread.holdsLock(this); 689 690 Iterator<CleanRequest> iter = pendingCleans.iterator(); 691 while (iter.hasNext()) { 692 CleanRequest request = iter.next(); 693 try { 694 dgc.clean(request.objIDs, request.sequenceNum, vmid, 695 request.strong); 696 iter.remove(); 697 } catch (Exception e) { 698 /* 699 * Many types of exceptions here could have been 700 * caused by a transient failure, so try again a 701 * few times, but not forever. 702 */ 703 if (++request.failures >= cleanFailureRetries) { 704 iter.remove(); 705 } 706 } 707 } 708 } 709 710 /** 711 * Create an array of ObjIDs (needed for the DGC remote calls) 712 * from the ids in the given set of refs. 713 */ 714 private static ObjID[] createObjIDArray(Set<RefEntry> refEntries) { 715 ObjID[] ids = new ObjID[refEntries.size()]; 716 Iterator<RefEntry> iter = refEntries.iterator(); 717 for (int i = 0; i < ids.length; i++) { 718 ids[i] = iter.next().getRef().getObjID(); 719 } 720 return ids; 721 } 722 723 /** 724 * RefEntry encapsulates the client-side DGC information specific 725 * to a particular LiveRef value. In particular, it contains a 726 * set of phantom references to all of the instances of the LiveRef 727 * value registered in the system (but not garbage collected 728 * locally). 729 */ 730 private class RefEntry { 731 732 /** LiveRef value for this entry (not a registered instance) */ 733 private LiveRef ref; 734 /** set of phantom references to registered instances */ 735 private Set<PhantomLiveRef> refSet = new HashSet<>(5); 736 /** true if a dirty call containing this ref has failed */ 737 private boolean dirtyFailed = false; 738 739 public RefEntry(LiveRef ref) { 740 this.ref = ref; 741 } 742 743 /** 744 * Return the LiveRef value for this entry (not a registered 745 * instance). 746 */ 747 public LiveRef getRef() { 748 return ref; 749 } 750 751 /** 752 * Add a LiveRef to the set of registered instances for this entry. 753 * 754 * This method must ONLY be invoked while synchronized on this 755 * RefEntry's EndpointEntry. 756 */ 757 public void addInstanceToRefSet(LiveRef ref) { 758 assert Thread.holdsLock(EndpointEntry.this); 759 assert ref.equals(this.ref); 760 761 /* 762 * Only keep a phantom reference to the registered instance, 763 * so that it can be garbage collected normally (and we can be 764 * notified when that happens). 765 */ 766 refSet.add(new PhantomLiveRef(ref)); 767 } 768 769 /** 770 * Remove a PhantomLiveRef from the set of registered instances. 771 * 772 * This method must ONLY be invoked while synchronized on this 773 * RefEntry's EndpointEntry. 774 */ 775 public void removeInstanceFromRefSet(PhantomLiveRef phantom) { 776 assert Thread.holdsLock(EndpointEntry.this); 777 assert refSet.contains(phantom); 778 refSet.remove(phantom); 779 } 780 781 /** 782 * Return true if there are no registered LiveRef instances for 783 * this entry still reachable in this VM. 784 * 785 * This method must ONLY be invoked while synchronized on this 786 * RefEntry's EndpointEntry. 787 */ 788 public boolean isRefSetEmpty() { 789 assert Thread.holdsLock(EndpointEntry.this); 790 return refSet.size() == 0; 791 } 792 793 /** 794 * Record that a dirty call that explicitly contained this 795 * entry's ref has failed. 796 * 797 * This method must ONLY be invoked while synchronized on this 798 * RefEntry's EndpointEntry. 799 */ 800 public void markDirtyFailed() { 801 assert Thread.holdsLock(EndpointEntry.this); 802 dirtyFailed = true; 803 } 804 805 /** 806 * Return true if a dirty call that explicitly contained this 807 * entry's ref has failed (and therefore a clean call for this 808 * ref needs to be marked "strong"). 809 * 810 * This method must ONLY be invoked while synchronized on this 811 * RefEntry's EndpointEntry. 812 */ 813 public boolean hasDirtyFailed() { 814 assert Thread.holdsLock(EndpointEntry.this); 815 return dirtyFailed; 816 } 817 818 /** 819 * PhantomLiveRef is a PhantomReference to a LiveRef instance, 820 * used to detect when the LiveRef becomes permanently 821 * unreachable in this VM. 822 */ 823 private class PhantomLiveRef extends PhantomReference<LiveRef> { 824 825 public PhantomLiveRef(LiveRef ref) { 826 super(ref, EndpointEntry.this.refQueue); 827 } 828 829 public RefEntry getRefEntry() { 830 return RefEntry.this; 831 } 832 } 833 } 834 } 835} 836