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 */ 25 package sun.rmi.transport; 26 27 import java.io.InvalidClassException; 28 import java.lang.ref.PhantomReference; 29 import java.lang.ref.ReferenceQueue; 30 import java.net.SocketPermission; 31 import java.rmi.UnmarshalException; 32 import java.security.AccessController; 33 import java.security.PrivilegedAction; 34 import java.util.HashMap; 35 import java.util.HashSet; 36 import java.util.Iterator; 37 import java.util.List; 38 import java.util.Map; 39 import java.util.Set; 40 import java.rmi.ConnectException; 41 import java.rmi.RemoteException; 42 import java.rmi.dgc.DGC; 43 import java.rmi.dgc.Lease; 44 import java.rmi.dgc.VMID; 45 import java.rmi.server.ObjID; 46 47 import sun.misc.GC; 48 import sun.rmi.runtime.Log; 49 import sun.rmi.runtime.NewThreadAction; 50 import sun.rmi.server.UnicastRef; 51 import sun.rmi.server.Util; 52 import sun.security.action.GetLongAction; 53 54 import java.security.AccessControlContext; 55 import java.security.Permissions; 56 import java.security.ProtectionDomain; 57 58 /** 59 * DGCClient implements the client-side of the RMI distributed garbage 60 * collection system. 61 * 62 * The external interface to DGCClient is the "registerRefs" method. 63 * When a LiveRef to a remote object enters the VM, it needs to be 64 * registered with the DGCClient to participate in distributed garbage 65 * collection. 66 * 67 * When the first LiveRef to a particular remote object is registered, 68 * a "dirty" call is made to the server-side distributed garbage 69 * collector for the remote object, which returns a lease guaranteeing 70 * that the server-side DGC will not collect the remote object for a 71 * certain period of time. While LiveRef instances to remote objects 72 * on a particular server exist, the DGCClient periodically sends more 73 * "dirty" calls to renew its lease. 74 * 75 * The DGCClient tracks the local reachability of registered LiveRef 76 * instances (using phantom references). When the LiveRef instance 77 * for a particular remote object becomes garbage collected locally, 78 * a "clean" call is made to the server-side distributed garbage 79 * collector, indicating that the server no longer needs to keep the 80 * remote object alive for this client. 81 * 82 * @see java.rmi.dgc.DGC, sun.rmi.transport.DGCImpl 83 * 84 * @author Ann Wollrath 85 * @author Peter Jones 86 */ 87 final class DGCClient { 88 89 /** next sequence number for DGC calls (access synchronized on class) */ 90 private static long nextSequenceNum = Long.MIN_VALUE; 91 92 /** unique identifier for this VM as a client of DGC */ 93 private static VMID vmid = new VMID(); 94 95 /** lease duration to request (usually ignored by server) */ 96 private static final long leaseValue = // default 10 minutes 97 AccessController.doPrivileged( 98 new GetLongAction("java.rmi.dgc.leaseValue", 99 600000)).longValue(); 100 101 /** maximum interval between retries of failed clean calls */ 102 private static final long cleanInterval = // default 3 minutes 103 AccessController.doPrivileged( 104 new GetLongAction("sun.rmi.dgc.cleanInterval", 105 180000)).longValue(); 106 107 /** maximum interval between complete garbage collections of local heap */ 108 private static final long gcInterval = // default 1 hour 109 AccessController.doPrivileged( 110 new GetLongAction("sun.rmi.dgc.client.gcInterval", 111 3600000)).longValue(); 112 113 /** minimum retry count for dirty calls that fail */ 114 private static final int dirtyFailureRetries = 5; 115 116 /** retry count for clean calls that fail with ConnectException */ 117 private static final int cleanFailureRetries = 5; 118 119 /** constant empty ObjID array for lease renewal optimization */ 120 private static final ObjID[] emptyObjIDArray = new ObjID[0]; 121 122 /** ObjID for server-side DGC object */ 123 private static final ObjID dgcID = new ObjID(ObjID.DGC_ID); 124 125 /** 126 * An AccessControlContext with only socket permissions, 127 * suitable for an RMIClientSocketFactory. 128 */ 129 private static final AccessControlContext SOCKET_ACC; 130 static { 131 Permissions perms = new Permissions(); perms.add(new SocketPermission(R, R))132 perms.add(new SocketPermission("*", "connect,resolve")); 133 ProtectionDomain[] pd = { new ProtectionDomain(null, perms) }; 134 SOCKET_ACC = new AccessControlContext(pd); 135 } 136 137 /* 138 * Disallow anyone from creating one of these. 139 */ DGCClient()140 private DGCClient() {} 141 142 /** 143 * Register the LiveRef instances in the supplied list to participate 144 * in distributed garbage collection. 145 * 146 * All of the LiveRefs in the list must be for remote objects at the 147 * given endpoint. 148 */ registerRefs(Endpoint ep, List<LiveRef> refs)149 static void registerRefs(Endpoint ep, List<LiveRef> refs) { 150 /* 151 * Look up the given endpoint and register the refs with it. 152 * The retrieved entry may get removed from the global endpoint 153 * table before EndpointEntry.registerRefs() is able to acquire 154 * its lock; in this event, it returns false, and we loop and 155 * try again. 156 */ 157 EndpointEntry epEntry; 158 do { 159 epEntry = EndpointEntry.lookup(ep); 160 } while (!epEntry.registerRefs(refs)); 161 } 162 163 /** 164 * Get the next sequence number to be used for a dirty or clean 165 * operation from this VM. This method should only be called while 166 * synchronized on the EndpointEntry whose data structures the 167 * operation affects. 168 */ getNextSequenceNum()169 private static synchronized long getNextSequenceNum() { 170 return nextSequenceNum++; 171 } 172 173 /** 174 * Given the length of a lease and the time that it was granted, 175 * compute the absolute time at which it should be renewed, giving 176 * room for reasonable computational and communication delays. 177 */ computeRenewTime(long grantTime, long duration)178 private static long computeRenewTime(long grantTime, long duration) { 179 /* 180 * REMIND: This algorithm should be more sophisticated, waiting 181 * a longer fraction of the lease duration for longer leases. 182 */ 183 return grantTime + (duration / 2); 184 } 185 186 /** 187 * EndpointEntry encapsulates the client-side DGC information specific 188 * to a particular Endpoint. Of most significance is the table that 189 * maps LiveRef value to RefEntry objects and the renew/clean thread 190 * that handles asynchronous client-side DGC operations. 191 */ 192 private static class EndpointEntry { 193 194 /** the endpoint that this entry is for */ 195 private Endpoint endpoint; 196 /** synthesized reference to the remote server-side DGC */ 197 private DGC dgc; 198 199 /** table of refs held for endpoint: maps LiveRef to RefEntry */ 200 private Map<LiveRef, RefEntry> refTable = new HashMap<>(5); 201 /** set of RefEntry instances from last (failed) dirty call */ 202 private Set<RefEntry> invalidRefs = new HashSet<>(5); 203 204 /** true if this entry has been removed from the global table */ 205 private boolean removed = false; 206 207 /** absolute time to renew current lease to this endpoint */ 208 private long renewTime = Long.MAX_VALUE; 209 /** absolute time current lease to this endpoint will expire */ 210 private long expirationTime = Long.MIN_VALUE; 211 /** count of recent dirty calls that have failed */ 212 private int dirtyFailures = 0; 213 /** absolute time of first recent failed dirty call */ 214 private long dirtyFailureStartTime; 215 /** (average) elapsed time for recent failed dirty calls */ 216 private long dirtyFailureDuration; 217 218 /** renew/clean thread for handling lease renewals and clean calls */ 219 private Thread renewCleanThread; 220 /** true if renew/clean thread may be interrupted */ 221 private boolean interruptible = false; 222 223 /** reference queue for phantom references */ 224 private ReferenceQueue<LiveRef> refQueue = new ReferenceQueue<>(); 225 /** set of clean calls that need to be made */ 226 private Set<CleanRequest> pendingCleans = new HashSet<>(5); 227 228 /** global endpoint table: maps Endpoint to EndpointEntry */ 229 private static Map<Endpoint,EndpointEntry> endpointTable = new HashMap<>(5); 230 /** handle for GC latency request (for future cancellation) */ 231 private static GC.LatencyRequest gcLatencyRequest = null; 232 233 /** 234 * Look up the EndpointEntry for the given Endpoint. An entry is 235 * created if one does not already exist. 236 */ lookup(Endpoint ep)237 public static EndpointEntry lookup(Endpoint ep) { 238 synchronized (endpointTable) { 239 EndpointEntry entry = endpointTable.get(ep); 240 if (entry == null) { 241 entry = new EndpointEntry(ep); 242 endpointTable.put(ep, entry); 243 /* 244 * While we are tracking live remote references registered 245 * in this VM, request a maximum latency for inspecting the 246 * entire heap from the local garbage collector, to place 247 * an upper bound on the time to discover remote references 248 * that have become unreachable (see bugid 4171278). 249 */ 250 if (gcLatencyRequest == null) { 251 gcLatencyRequest = GC.requestLatency(gcInterval); 252 } 253 } 254 return entry; 255 } 256 } 257 EndpointEntry(final Endpoint endpoint)258 private EndpointEntry(final Endpoint endpoint) { 259 this.endpoint = endpoint; 260 try { 261 LiveRef dgcRef = new LiveRef(dgcID, endpoint, false); 262 dgc = (DGC) Util.createProxy(DGCImpl.class, 263 new UnicastRef(dgcRef), true); 264 } catch (RemoteException e) { 265 throw new Error("internal error creating DGC stub"); 266 } 267 renewCleanThread = AccessController.doPrivileged( 268 new NewThreadAction(new RenewCleanThread(), 269 "RenewClean-" + endpoint, true)); 270 renewCleanThread.start(); 271 } 272 273 /** 274 * Register the LiveRef instances in the supplied list to participate 275 * in distributed garbage collection. 276 * 277 * This method returns false if this entry was removed from the 278 * global endpoint table (because it was empty) before these refs 279 * could be registered. In that case, a new EndpointEntry needs 280 * to be looked up. 281 * 282 * This method must NOT be called while synchronized on this entry. 283 */ registerRefs(List<LiveRef> refs)284 public boolean registerRefs(List<LiveRef> refs) { 285 assert !Thread.holdsLock(this); 286 287 Set<RefEntry> refsToDirty = null; // entries for refs needing dirty 288 long sequenceNum; // sequence number for dirty call 289 290 synchronized (this) { 291 if (removed) { 292 return false; 293 } 294 295 Iterator<LiveRef> iter = refs.iterator(); 296 while (iter.hasNext()) { 297 LiveRef ref = iter.next(); 298 assert ref.getEndpoint().equals(endpoint); 299 300 RefEntry refEntry = refTable.get(ref); 301 if (refEntry == null) { 302 LiveRef refClone = (LiveRef) ref.clone(); 303 refEntry = new RefEntry(refClone); 304 refTable.put(refClone, refEntry); 305 if (refsToDirty == null) { 306 refsToDirty = new HashSet<>(5); 307 } 308 refsToDirty.add(refEntry); 309 } 310 311 refEntry.addInstanceToRefSet(ref); 312 } 313 314 if (refsToDirty == null) { 315 return true; 316 } 317 318 refsToDirty.addAll(invalidRefs); 319 invalidRefs.clear(); 320 321 sequenceNum = getNextSequenceNum(); 322 } 323 324 makeDirtyCall(refsToDirty, sequenceNum); 325 return true; 326 } 327 328 /** 329 * Remove the given RefEntry from the ref table. If that makes 330 * the ref table empty, remove this entry from the global endpoint 331 * table. 332 * 333 * This method must ONLY be called while synchronized on this entry. 334 */ removeRefEntry(RefEntry refEntry)335 private void removeRefEntry(RefEntry refEntry) { 336 assert Thread.holdsLock(this); 337 assert !removed; 338 assert refTable.containsKey(refEntry.getRef()); 339 340 refTable.remove(refEntry.getRef()); 341 invalidRefs.remove(refEntry); 342 if (refTable.isEmpty()) { 343 synchronized (endpointTable) { 344 endpointTable.remove(endpoint); 345 Transport transport = endpoint.getOutboundTransport(); 346 transport.free(endpoint); 347 /* 348 * If there are no longer any live remote references 349 * registered, we are no longer concerned with the 350 * latency of local garbage collection here. 351 */ 352 if (endpointTable.isEmpty()) { 353 assert gcLatencyRequest != null; 354 gcLatencyRequest.cancel(); 355 gcLatencyRequest = null; 356 } 357 removed = true; 358 } 359 } 360 } 361 362 /** 363 * Make a DGC dirty call to this entry's endpoint, for the ObjIDs 364 * corresponding to the given set of refs and with the given 365 * sequence number. 366 * 367 * This method must NOT be called while synchronized on this entry. 368 */ makeDirtyCall(Set<RefEntry> refEntries, long sequenceNum)369 private void makeDirtyCall(Set<RefEntry> refEntries, long sequenceNum) { 370 assert !Thread.holdsLock(this); 371 372 ObjID[] ids; 373 if (refEntries != null) { 374 ids = createObjIDArray(refEntries); 375 } else { 376 ids = emptyObjIDArray; 377 } 378 379 long startTime = System.currentTimeMillis(); 380 try { 381 Lease lease = 382 dgc.dirty(ids, sequenceNum, new Lease(vmid, leaseValue)); 383 long duration = lease.getValue(); 384 385 long newRenewTime = computeRenewTime(startTime, duration); 386 long newExpirationTime = startTime + duration; 387 388 synchronized (this) { 389 dirtyFailures = 0; 390 setRenewTime(newRenewTime); 391 expirationTime = newExpirationTime; 392 } 393 394 } catch (Exception e) { 395 long endTime = System.currentTimeMillis(); 396 397 synchronized (this) { 398 dirtyFailures++; 399 400 if (e instanceof UnmarshalException 401 && e.getCause() instanceof InvalidClassException) { 402 DGCImpl.dgcLog.log(Log.BRIEF, "InvalidClassException exception in DGC dirty call", e); 403 return; // protocol error, do not register these refs 404 } 405 406 if (dirtyFailures == 1) { 407 /* 408 * If this was the first recent failed dirty call, 409 * reschedule another one immediately, in case there 410 * was just a transient network problem, and remember 411 * the start time and duration of this attempt for 412 * future calculations of the delays between retries. 413 */ 414 dirtyFailureStartTime = startTime; 415 dirtyFailureDuration = endTime - startTime; 416 setRenewTime(endTime); 417 } else { 418 /* 419 * For each successive failed dirty call, wait for a 420 * (binary) exponentially increasing delay before 421 * retrying, to avoid network congestion. 422 */ 423 int n = dirtyFailures - 2; 424 if (n == 0) { 425 /* 426 * Calculate the initial retry delay from the 427 * average time elapsed for each of the first 428 * two failed dirty calls. The result must be 429 * at least 1000ms, to prevent a tight loop. 430 */ 431 dirtyFailureDuration = 432 Math.max((dirtyFailureDuration + 433 (endTime - startTime)) >> 1, 1000); 434 } 435 long newRenewTime = 436 endTime + (dirtyFailureDuration << n); 437 438 /* 439 * Continue if the last known held lease has not 440 * expired, or else at least a fixed number of times, 441 * or at least until we've tried for a fixed amount 442 * of time (the default lease value we request). 443 */ 444 if (newRenewTime < expirationTime || 445 dirtyFailures < dirtyFailureRetries || 446 newRenewTime < dirtyFailureStartTime + leaseValue) 447 { 448 setRenewTime(newRenewTime); 449 } else { 450 /* 451 * Give up: postpone lease renewals until next 452 * ref is registered for this endpoint. 453 */ 454 setRenewTime(Long.MAX_VALUE); 455 } 456 } 457 458 if (refEntries != null) { 459 /* 460 * Add all of these refs to the set of refs for this 461 * endpoint that may be invalid (this VM may not be in 462 * the server's referenced set), so that we will 463 * attempt to explicitly dirty them again in the 464 * future. 465 */ 466 invalidRefs.addAll(refEntries); 467 468 /* 469 * Record that a dirty call has failed for all of these 470 * refs, so that clean calls for them in the future 471 * will be strong. 472 */ 473 Iterator<RefEntry> iter = refEntries.iterator(); 474 while (iter.hasNext()) { 475 RefEntry refEntry = iter.next(); 476 refEntry.markDirtyFailed(); 477 } 478 } 479 480 /* 481 * If the last known held lease will have expired before 482 * the next renewal, all refs might be invalid. 483 */ 484 if (renewTime >= expirationTime) { 485 invalidRefs.addAll(refTable.values()); 486 } 487 } 488 } 489 } 490 491 /** 492 * Set the absolute time at which the lease for this entry should 493 * be renewed. 494 * 495 * This method must ONLY be called while synchronized on this entry. 496 */ setRenewTime(long newRenewTime)497 private void setRenewTime(long newRenewTime) { 498 assert Thread.holdsLock(this); 499 500 if (newRenewTime < renewTime) { 501 renewTime = newRenewTime; 502 if (interruptible) { 503 AccessController.doPrivileged( 504 new PrivilegedAction<Void>() { 505 public Void run() { 506 renewCleanThread.interrupt(); 507 return null; 508 } 509 }); 510 } 511 } else { 512 renewTime = newRenewTime; 513 } 514 } 515 516 /** 517 * RenewCleanThread handles the asynchronous client-side DGC activity 518 * for this entry: renewing the leases and making clean calls. 519 */ 520 private class RenewCleanThread implements Runnable { 521 run()522 public void run() { 523 do { 524 long timeToWait; 525 RefEntry.PhantomLiveRef phantom = null; 526 boolean needRenewal = false; 527 Set<RefEntry> refsToDirty = null; 528 long sequenceNum = Long.MIN_VALUE; 529 530 synchronized (EndpointEntry.this) { 531 /* 532 * Calculate time to block (waiting for phantom 533 * reference notifications). It is the time until the 534 * lease renewal should be done, bounded on the low 535 * end by 1 ms so that the reference queue will always 536 * get processed, and if there are pending clean 537 * requests (remaining because some clean calls 538 * failed), bounded on the high end by the maximum 539 * clean call retry interval. 540 */ 541 long timeUntilRenew = 542 renewTime - System.currentTimeMillis(); 543 timeToWait = Math.max(timeUntilRenew, 1); 544 if (!pendingCleans.isEmpty()) { 545 timeToWait = Math.min(timeToWait, cleanInterval); 546 } 547 548 /* 549 * Set flag indicating that it is OK to interrupt this 550 * thread now, such as if a earlier lease renewal time 551 * is set, because we are only going to be blocking 552 * and can deal with interrupts. 553 */ 554 interruptible = true; 555 } 556 557 try { 558 /* 559 * Wait for the duration calculated above for any of 560 * our phantom references to be enqueued. 561 */ 562 phantom = (RefEntry.PhantomLiveRef) 563 refQueue.remove(timeToWait); 564 } catch (InterruptedException e) { 565 } 566 567 synchronized (EndpointEntry.this) { 568 /* 569 * Set flag indicating that it is NOT OK to interrupt 570 * this thread now, because we may be undertaking I/O 571 * operations that should not be interrupted (and we 572 * will not be blocking arbitrarily). 573 */ 574 interruptible = false; 575 Thread.interrupted(); // clear interrupted state 576 577 /* 578 * If there was a phantom reference enqueued, process 579 * it and all the rest on the queue, generating 580 * clean requests as necessary. 581 */ 582 if (phantom != null) { 583 processPhantomRefs(phantom); 584 } 585 586 /* 587 * Check if it is time to renew this entry's lease. 588 */ 589 long currentTime = System.currentTimeMillis(); 590 if (currentTime > renewTime) { 591 needRenewal = true; 592 if (!invalidRefs.isEmpty()) { 593 refsToDirty = invalidRefs; 594 invalidRefs = new HashSet<>(5); 595 } 596 sequenceNum = getNextSequenceNum(); 597 } 598 } 599 600 boolean needRenewal_ = needRenewal; 601 Set<RefEntry> refsToDirty_ = refsToDirty; 602 long sequenceNum_ = sequenceNum; 603 AccessController.doPrivileged(new PrivilegedAction<Void>() { 604 public Void run() { 605 if (needRenewal_) { 606 makeDirtyCall(refsToDirty_, sequenceNum_); 607 } 608 609 if (!pendingCleans.isEmpty()) { 610 makeCleanCalls(); 611 } 612 return null; 613 }}, SOCKET_ACC); 614 } while (!removed || !pendingCleans.isEmpty()); 615 } 616 } 617 618 /** 619 * Process the notification of the given phantom reference and any 620 * others that are on this entry's reference queue. Each phantom 621 * reference is removed from its RefEntry's ref set. All ref 622 * entries that have no more registered instances are collected 623 * into up to two batched clean call requests: one for refs 624 * requiring a "strong" clean call, and one for the rest. 625 * 626 * This method must ONLY be called while synchronized on this entry. 627 */ processPhantomRefs(RefEntry.PhantomLiveRef phantom)628 private void processPhantomRefs(RefEntry.PhantomLiveRef phantom) { 629 assert Thread.holdsLock(this); 630 631 Set<RefEntry> strongCleans = null; 632 Set<RefEntry> normalCleans = null; 633 634 do { 635 RefEntry refEntry = phantom.getRefEntry(); 636 refEntry.removeInstanceFromRefSet(phantom); 637 if (refEntry.isRefSetEmpty()) { 638 if (refEntry.hasDirtyFailed()) { 639 if (strongCleans == null) { 640 strongCleans = new HashSet<>(5); 641 } 642 strongCleans.add(refEntry); 643 } else { 644 if (normalCleans == null) { 645 normalCleans = new HashSet<>(5); 646 } 647 normalCleans.add(refEntry); 648 } 649 removeRefEntry(refEntry); 650 } 651 } while ((phantom = 652 (RefEntry.PhantomLiveRef) refQueue.poll()) != null); 653 654 if (strongCleans != null) { 655 pendingCleans.add( 656 new CleanRequest(createObjIDArray(strongCleans), 657 getNextSequenceNum(), true)); 658 } 659 if (normalCleans != null) { 660 pendingCleans.add( 661 new CleanRequest(createObjIDArray(normalCleans), 662 getNextSequenceNum(), false)); 663 } 664 } 665 666 /** 667 * CleanRequest holds the data for the parameters of a clean call 668 * that needs to be made. 669 */ 670 private static class CleanRequest { 671 672 final ObjID[] objIDs; 673 final long sequenceNum; 674 final boolean strong; 675 676 /** how many times this request has failed */ 677 int failures = 0; 678 CleanRequest(ObjID[] objIDs, long sequenceNum, boolean strong)679 CleanRequest(ObjID[] objIDs, long sequenceNum, boolean strong) { 680 this.objIDs = objIDs; 681 this.sequenceNum = sequenceNum; 682 this.strong = strong; 683 } 684 } 685 686 /** 687 * Make all of the clean calls described by the clean requests in 688 * this entry's set of "pending cleans". Clean requests for clean 689 * calls that succeed are removed from the "pending cleans" set. 690 * 691 * This method must NOT be called while synchronized on this entry. 692 */ makeCleanCalls()693 private void makeCleanCalls() { 694 assert !Thread.holdsLock(this); 695 696 Iterator<CleanRequest> iter = pendingCleans.iterator(); 697 while (iter.hasNext()) { 698 CleanRequest request = iter.next(); 699 try { 700 dgc.clean(request.objIDs, request.sequenceNum, vmid, 701 request.strong); 702 iter.remove(); 703 } catch (Exception e) { 704 /* 705 * Many types of exceptions here could have been 706 * caused by a transient failure, so try again a 707 * few times, but not forever. 708 */ 709 if (++request.failures >= cleanFailureRetries) { 710 iter.remove(); 711 } 712 } 713 } 714 } 715 716 /** 717 * Create an array of ObjIDs (needed for the DGC remote calls) 718 * from the ids in the given set of refs. 719 */ createObjIDArray(Set<RefEntry> refEntries)720 private static ObjID[] createObjIDArray(Set<RefEntry> refEntries) { 721 ObjID[] ids = new ObjID[refEntries.size()]; 722 Iterator<RefEntry> iter = refEntries.iterator(); 723 for (int i = 0; i < ids.length; i++) { 724 ids[i] = iter.next().getRef().getObjID(); 725 } 726 return ids; 727 } 728 729 /** 730 * RefEntry encapsulates the client-side DGC information specific 731 * to a particular LiveRef value. In particular, it contains a 732 * set of phantom references to all of the instances of the LiveRef 733 * value registered in the system (but not garbage collected 734 * locally). 735 */ 736 private class RefEntry { 737 738 /** LiveRef value for this entry (not a registered instance) */ 739 private LiveRef ref; 740 /** set of phantom references to registered instances */ 741 private Set<PhantomLiveRef> refSet = new HashSet<>(5); 742 /** true if a dirty call containing this ref has failed */ 743 private boolean dirtyFailed = false; 744 RefEntry(LiveRef ref)745 public RefEntry(LiveRef ref) { 746 this.ref = ref; 747 } 748 749 /** 750 * Return the LiveRef value for this entry (not a registered 751 * instance). 752 */ getRef()753 public LiveRef getRef() { 754 return ref; 755 } 756 757 /** 758 * Add a LiveRef to the set of registered instances for this entry. 759 * 760 * This method must ONLY be invoked while synchronized on this 761 * RefEntry's EndpointEntry. 762 */ addInstanceToRefSet(LiveRef ref)763 public void addInstanceToRefSet(LiveRef ref) { 764 assert Thread.holdsLock(EndpointEntry.this); 765 assert ref.equals(this.ref); 766 767 /* 768 * Only keep a phantom reference to the registered instance, 769 * so that it can be garbage collected normally (and we can be 770 * notified when that happens). 771 */ 772 refSet.add(new PhantomLiveRef(ref)); 773 } 774 775 /** 776 * Remove a PhantomLiveRef from the set of registered instances. 777 * 778 * This method must ONLY be invoked while synchronized on this 779 * RefEntry's EndpointEntry. 780 */ removeInstanceFromRefSet(PhantomLiveRef phantom)781 public void removeInstanceFromRefSet(PhantomLiveRef phantom) { 782 assert Thread.holdsLock(EndpointEntry.this); 783 assert refSet.contains(phantom); 784 refSet.remove(phantom); 785 } 786 787 /** 788 * Return true if there are no registered LiveRef instances for 789 * this entry still reachable in this VM. 790 * 791 * This method must ONLY be invoked while synchronized on this 792 * RefEntry's EndpointEntry. 793 */ isRefSetEmpty()794 public boolean isRefSetEmpty() { 795 assert Thread.holdsLock(EndpointEntry.this); 796 return refSet.size() == 0; 797 } 798 799 /** 800 * Record that a dirty call that explicitly contained this 801 * entry's ref has failed. 802 * 803 * This method must ONLY be invoked while synchronized on this 804 * RefEntry's EndpointEntry. 805 */ markDirtyFailed()806 public void markDirtyFailed() { 807 assert Thread.holdsLock(EndpointEntry.this); 808 dirtyFailed = true; 809 } 810 811 /** 812 * Return true if a dirty call that explicitly contained this 813 * entry's ref has failed (and therefore a clean call for this 814 * ref needs to be marked "strong"). 815 * 816 * This method must ONLY be invoked while synchronized on this 817 * RefEntry's EndpointEntry. 818 */ hasDirtyFailed()819 public boolean hasDirtyFailed() { 820 assert Thread.holdsLock(EndpointEntry.this); 821 return dirtyFailed; 822 } 823 824 /** 825 * PhantomLiveRef is a PhantomReference to a LiveRef instance, 826 * used to detect when the LiveRef becomes permanently 827 * unreachable in this VM. 828 */ 829 private class PhantomLiveRef extends PhantomReference<LiveRef> { 830 PhantomLiveRef(LiveRef ref)831 public PhantomLiveRef(LiveRef ref) { 832 super(ref, EndpointEntry.this.refQueue); 833 } 834 getRefEntry()835 public RefEntry getRefEntry() { 836 return RefEntry.this; 837 } 838 } 839 } 840 } 841 } 842