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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 | } | ||