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| 1 | /* | ||
| 2 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 3 | * | ||
| 4 | * This code is free software; you can redistribute it and/or modify it | ||
| 5 | * under the terms of the GNU General Public License version 2 only, as | ||
| 6 | * published by the Free Software Foundation. Oracle designates this | ||
| 7 | * particular file as subject to the "Classpath" exception as provided | ||
| 8 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 9 | * | ||
| 10 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 11 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 12 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 13 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 14 | * accompanied this code). | ||
| 15 | * | ||
| 16 | * You should have received a copy of the GNU General Public License version | ||
| 17 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 18 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 19 | * | ||
| 20 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 21 | * or visit www.oracle.com if you need additional information or have any | ||
| 22 | * questions. | ||
| 23 | */ | ||
| 24 | |||
| 25 | /* | ||
| 26 | * This file is available under and governed by the GNU General Public | ||
| 27 | * License version 2 only, as published by the Free Software Foundation. | ||
| 28 | * However, the following notice accompanied the original version of this | ||
| 29 | * file: | ||
| 30 | * | ||
| 31 | * Written by Doug Lea with assistance from members of JCP JSR-166 | ||
| 32 | * Expert Group and released to the public domain, as explained at | ||
| 33 | * http://creativecommons.org/publicdomain/zero/1.0/ | ||
| 34 | */ | ||
| 35 | |||
| 36 | package java.util.concurrent; | ||
| 37 | |||
| 38 | import java.util.concurrent.TimeUnit; | ||
| 39 | import java.util.concurrent.TimeoutException; | ||
| 40 | import java.util.concurrent.atomic.AtomicReference; | ||
| 41 | import java.util.concurrent.locks.LockSupport; | ||
| 42 | |||
| 43 | /** | ||
| 44 | * A reusable synchronization barrier, similar in functionality to | ||
| 45 | * {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and | ||
| 46 | * {@link java.util.concurrent.CountDownLatch CountDownLatch} | ||
| 47 | * but supporting more flexible usage. | ||
| 48 | * | ||
| 49 | * <p> <b>Registration.</b> Unlike the case for other barriers, the | ||
| 50 | * number of parties <em>registered</em> to synchronize on a phaser | ||
| 51 | * may vary over time. Tasks may be registered at any time (using | ||
| 52 | * methods {@link #register}, {@link #bulkRegister}, or forms of | ||
| 53 | * constructors establishing initial numbers of parties), and | ||
| 54 | * optionally deregistered upon any arrival (using {@link | ||
| 55 | * #arriveAndDeregister}). As is the case with most basic | ||
| 56 | * synchronization constructs, registration and deregistration affect | ||
| 57 | * only internal counts; they do not establish any further internal | ||
| 58 | * bookkeeping, so tasks cannot query whether they are registered. | ||
| 59 | * (However, you can introduce such bookkeeping by subclassing this | ||
| 60 | * class.) | ||
| 61 | * | ||
| 62 | * <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code | ||
| 63 | * Phaser} may be repeatedly awaited. Method {@link | ||
| 64 | * #arriveAndAwaitAdvance} has effect analogous to {@link | ||
| 65 | * java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each | ||
| 66 | * generation of a phaser has an associated phase number. The phase | ||
| 67 | * number starts at zero, and advances when all parties arrive at the | ||
| 68 | * phaser, wrapping around to zero after reaching {@code | ||
| 69 | * Integer.MAX_VALUE}. The use of phase numbers enables independent | ||
| 70 | * control of actions upon arrival at a phaser and upon awaiting | ||
| 71 | * others, via two kinds of methods that may be invoked by any | ||
| 72 | * registered party: | ||
| 73 | * | ||
| 74 | * <ul> | ||
| 75 | * | ||
| 76 | * <li> <b>Arrival.</b> Methods {@link #arrive} and | ||
| 77 | * {@link #arriveAndDeregister} record arrival. These methods | ||
| 78 | * do not block, but return an associated <em>arrival phase | ||
| 79 | * number</em>; that is, the phase number of the phaser to which | ||
| 80 | * the arrival applied. When the final party for a given phase | ||
| 81 | * arrives, an optional action is performed and the phase | ||
| 82 | * advances. These actions are performed by the party | ||
| 83 | * triggering a phase advance, and are arranged by overriding | ||
| 84 | * method {@link #onAdvance(int, int)}, which also controls | ||
| 85 | * termination. Overriding this method is similar to, but more | ||
| 86 | * flexible than, providing a barrier action to a {@code | ||
| 87 | * CyclicBarrier}. | ||
| 88 | * | ||
| 89 | * <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an | ||
| 90 | * argument indicating an arrival phase number, and returns when | ||
| 91 | * the phaser advances to (or is already at) a different phase. | ||
| 92 | * Unlike similar constructions using {@code CyclicBarrier}, | ||
| 93 | * method {@code awaitAdvance} continues to wait even if the | ||
| 94 | * waiting thread is interrupted. Interruptible and timeout | ||
| 95 | * versions are also available, but exceptions encountered while | ||
| 96 | * tasks wait interruptibly or with timeout do not change the | ||
| 97 | * state of the phaser. If necessary, you can perform any | ||
| 98 | * associated recovery within handlers of those exceptions, | ||
| 99 | * often after invoking {@code forceTermination}. Phasers may | ||
| 100 | * also be used by tasks executing in a {@link ForkJoinPool}, | ||
| 101 | * which will ensure sufficient parallelism to execute tasks | ||
| 102 | * when others are blocked waiting for a phase to advance. | ||
| 103 | * | ||
| 104 | * </ul> | ||
| 105 | * | ||
| 106 | * <p> <b>Termination.</b> A phaser may enter a <em>termination</em> | ||
| 107 | * state, that may be checked using method {@link #isTerminated}. Upon | ||
| 108 | * termination, all synchronization methods immediately return without | ||
| 109 | * waiting for advance, as indicated by a negative return value. | ||
| 110 | * Similarly, attempts to register upon termination have no effect. | ||
| 111 | * Termination is triggered when an invocation of {@code onAdvance} | ||
| 112 | * returns {@code true}. The default implementation returns {@code | ||
| 113 | * true} if a deregistration has caused the number of registered | ||
| 114 | * parties to become zero. As illustrated below, when phasers control | ||
| 115 | * actions with a fixed number of iterations, it is often convenient | ||
| 116 | * to override this method to cause termination when the current phase | ||
| 117 | * number reaches a threshold. Method {@link #forceTermination} is | ||
| 118 | * also available to abruptly release waiting threads and allow them | ||
| 119 | * to terminate. | ||
| 120 | * | ||
| 121 | * <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., | ||
| 122 | * constructed in tree structures) to reduce contention. Phasers with | ||
| 123 | * large numbers of parties that would otherwise experience heavy | ||
| 124 | * synchronization contention costs may instead be set up so that | ||
| 125 | * groups of sub-phasers share a common parent. This may greatly | ||
| 126 | * increase throughput even though it incurs greater per-operation | ||
| 127 | * overhead. | ||
| 128 | * | ||
| 129 | * <p>In a tree of tiered phasers, registration and deregistration of | ||
| 130 | * child phasers with their parent are managed automatically. | ||
| 131 | * Whenever the number of registered parties of a child phaser becomes | ||
| 132 | * non-zero (as established in the {@link #Phaser(Phaser,int)} | ||
| 133 | * constructor, {@link #register}, or {@link #bulkRegister}), the | ||
| 134 | * child phaser is registered with its parent. Whenever the number of | ||
| 135 | * registered parties becomes zero as the result of an invocation of | ||
| 136 | * {@link #arriveAndDeregister}, the child phaser is deregistered | ||
| 137 | * from its parent. | ||
| 138 | * | ||
| 139 | * <p><b>Monitoring.</b> While synchronization methods may be invoked | ||
| 140 | * only by registered parties, the current state of a phaser may be | ||
| 141 | * monitored by any caller. At any given moment there are {@link | ||
| 142 | * #getRegisteredParties} parties in total, of which {@link | ||
| 143 | * #getArrivedParties} have arrived at the current phase ({@link | ||
| 144 | * #getPhase}). When the remaining ({@link #getUnarrivedParties}) | ||
| 145 | * parties arrive, the phase advances. The values returned by these | ||
| 146 | * methods may reflect transient states and so are not in general | ||
| 147 | * useful for synchronization control. Method {@link #toString} | ||
| 148 | * returns snapshots of these state queries in a form convenient for | ||
| 149 | * informal monitoring. | ||
| 150 | * | ||
| 151 | * <p><b>Sample usages:</b> | ||
| 152 | * | ||
| 153 | * <p>A {@code Phaser} may be used instead of a {@code CountDownLatch} | ||
| 154 | * to control a one-shot action serving a variable number of parties. | ||
| 155 | * The typical idiom is for the method setting this up to first | ||
| 156 | * register, then start the actions, then deregister, as in: | ||
| 157 | * | ||
| 158 | * <pre> {@code | ||
| 159 | * void runTasks(List<Runnable> tasks) { | ||
| 160 | * final Phaser phaser = new Phaser(1); // "1" to register self | ||
| 161 | * // create and start threads | ||
| 162 | * for (final Runnable task : tasks) { | ||
| 163 | * phaser.register(); | ||
| 164 | * new Thread() { | ||
| 165 | * public void run() { | ||
| 166 | * phaser.arriveAndAwaitAdvance(); // await all creation | ||
| 167 | * task.run(); | ||
| 168 | * } | ||
| 169 | * }.start(); | ||
| 170 | * } | ||
| 171 | * | ||
| 172 | * // allow threads to start and deregister self | ||
| 173 | * phaser.arriveAndDeregister(); | ||
| 174 | * }}</pre> | ||
| 175 | * | ||
| 176 | * <p>One way to cause a set of threads to repeatedly perform actions | ||
| 177 | * for a given number of iterations is to override {@code onAdvance}: | ||
| 178 | * | ||
| 179 | * <pre> {@code | ||
| 180 | * void startTasks(List<Runnable> tasks, final int iterations) { | ||
| 181 | * final Phaser phaser = new Phaser() { | ||
| 182 | * protected boolean onAdvance(int phase, int registeredParties) { | ||
| 183 | * return phase >= iterations || registeredParties == 0; | ||
| 184 | * } | ||
| 185 | * }; | ||
| 186 | * phaser.register(); | ||
| 187 | * for (final Runnable task : tasks) { | ||
| 188 | * phaser.register(); | ||
| 189 | * new Thread() { | ||
| 190 | * public void run() { | ||
| 191 | * do { | ||
| 192 | * task.run(); | ||
| 193 | * phaser.arriveAndAwaitAdvance(); | ||
| 194 | * } while (!phaser.isTerminated()); | ||
| 195 | * } | ||
| 196 | * }.start(); | ||
| 197 | * } | ||
| 198 | * phaser.arriveAndDeregister(); // deregister self, don't wait | ||
| 199 | * }}</pre> | ||
| 200 | * | ||
| 201 | * If the main task must later await termination, it | ||
| 202 | * may re-register and then execute a similar loop: | ||
| 203 | * <pre> {@code | ||
| 204 | * // ... | ||
| 205 | * phaser.register(); | ||
| 206 | * while (!phaser.isTerminated()) | ||
| 207 | * phaser.arriveAndAwaitAdvance();}</pre> | ||
| 208 | * | ||
| 209 | * <p>Related constructions may be used to await particular phase numbers | ||
| 210 | * in contexts where you are sure that the phase will never wrap around | ||
| 211 | * {@code Integer.MAX_VALUE}. For example: | ||
| 212 | * | ||
| 213 | * <pre> {@code | ||
| 214 | * void awaitPhase(Phaser phaser, int phase) { | ||
| 215 | * int p = phaser.register(); // assumes caller not already registered | ||
| 216 | * while (p < phase) { | ||
| 217 | * if (phaser.isTerminated()) | ||
| 218 | * // ... deal with unexpected termination | ||
| 219 | * else | ||
| 220 | * p = phaser.arriveAndAwaitAdvance(); | ||
| 221 | * } | ||
| 222 | * phaser.arriveAndDeregister(); | ||
| 223 | * }}</pre> | ||
| 224 | * | ||
| 225 | * | ||
| 226 | * <p>To create a set of {@code n} tasks using a tree of phasers, you | ||
| 227 | * could use code of the following form, assuming a Task class with a | ||
| 228 | * constructor accepting a {@code Phaser} that it registers with upon | ||
| 229 | * construction. After invocation of {@code build(new Task[n], 0, n, | ||
| 230 | * new Phaser())}, these tasks could then be started, for example by | ||
| 231 | * submitting to a pool: | ||
| 232 | * | ||
| 233 | * <pre> {@code | ||
| 234 | * void build(Task[] tasks, int lo, int hi, Phaser ph) { | ||
| 235 | * if (hi - lo > TASKS_PER_PHASER) { | ||
| 236 | * for (int i = lo; i < hi; i += TASKS_PER_PHASER) { | ||
| 237 | * int j = Math.min(i + TASKS_PER_PHASER, hi); | ||
| 238 | * build(tasks, i, j, new Phaser(ph)); | ||
| 239 | * } | ||
| 240 | * } else { | ||
| 241 | * for (int i = lo; i < hi; ++i) | ||
| 242 | * tasks[i] = new Task(ph); | ||
| 243 | * // assumes new Task(ph) performs ph.register() | ||
| 244 | * } | ||
| 245 | * }}</pre> | ||
| 246 | * | ||
| 247 | * The best value of {@code TASKS_PER_PHASER} depends mainly on | ||
| 248 | * expected synchronization rates. A value as low as four may | ||
| 249 | * be appropriate for extremely small per-phase task bodies (thus | ||
| 250 | * high rates), or up to hundreds for extremely large ones. | ||
| 251 | * | ||
| 252 | * <p><b>Implementation notes</b>: This implementation restricts the | ||
| 253 | * maximum number of parties to 65535. Attempts to register additional | ||
| 254 | * parties result in {@code IllegalStateException}. However, you can and | ||
| 255 | * should create tiered phasers to accommodate arbitrarily large sets | ||
| 256 | * of participants. | ||
| 257 | * | ||
| 258 | * @since 1.7 | ||
| 259 | * @author Doug Lea | ||
| 260 | */ | ||
| 261 | public class Phaser { | ||
| 262 | /* | ||
| 263 | * This class implements an extension of X10 "clocks". Thanks to | ||
| 264 | * Vijay Saraswat for the idea, and to Vivek Sarkar for | ||
| 265 | * enhancements to extend functionality. | ||
| 266 | */ | ||
| 267 | |||
| 268 | /** | ||
| 269 | * Primary state representation, holding four bit-fields: | ||
| 270 | * | ||
| 271 | * unarrived -- the number of parties yet to hit barrier (bits 0-15) | ||
| 272 | * parties -- the number of parties to wait (bits 16-31) | ||
| 273 | * phase -- the generation of the barrier (bits 32-62) | ||
| 274 | * terminated -- set if barrier is terminated (bit 63 / sign) | ||
| 275 | * | ||
| 276 | * Except that a phaser with no registered parties is | ||
| 277 | * distinguished by the otherwise illegal state of having zero | ||
| 278 | * parties and one unarrived parties (encoded as EMPTY below). | ||
| 279 | * | ||
| 280 | * To efficiently maintain atomicity, these values are packed into | ||
| 281 | * a single (atomic) long. Good performance relies on keeping | ||
| 282 | * state decoding and encoding simple, and keeping race windows | ||
| 283 | * short. | ||
| 284 | * | ||
| 285 | * All state updates are performed via CAS except initial | ||
| 286 | * registration of a sub-phaser (i.e., one with a non-null | ||
| 287 | * parent). In this (relatively rare) case, we use built-in | ||
| 288 | * synchronization to lock while first registering with its | ||
| 289 | * parent. | ||
| 290 | * | ||
| 291 | * The phase of a subphaser is allowed to lag that of its | ||
| 292 | * ancestors until it is actually accessed -- see method | ||
| 293 | * reconcileState. | ||
| 294 | */ | ||
| 295 | private volatile long state; | ||
| 296 | |||
| 297 | private static final int MAX_PARTIES = 0xffff; | ||
| 298 | private static final int MAX_PHASE = Integer.MAX_VALUE; | ||
| 299 | private static final int PARTIES_SHIFT = 16; | ||
| 300 | private static final int PHASE_SHIFT = 32; | ||
| 301 | private static final int UNARRIVED_MASK = 0xffff; // to mask ints | ||
| 302 | private static final long PARTIES_MASK = 0xffff0000L; // to mask longs | ||
| 303 | private static final long TERMINATION_BIT = 1L << 63; | ||
| 304 | |||
| 305 | // some special values | ||
| 306 | private static final int ONE_ARRIVAL = 1; | ||
| 307 | private static final int ONE_PARTY = 1 << PARTIES_SHIFT; | ||
| 308 | private static final int EMPTY = 1; | ||
| 309 | |||
| 310 | // The following unpacking methods are usually manually inlined | ||
| 311 | |||
| 312 | private static int unarrivedOf(long s) { | ||
| 313 | int counts = (int)s; | ||
| 314 | return (counts == EMPTY) ? 0 : counts & UNARRIVED_MASK; | ||
| 315 | } | ||
| 316 | |||
| 317 | private static int partiesOf(long s) { | ||
| 318 | return (int)s >>> PARTIES_SHIFT; | ||
| 319 | } | ||
| 320 | |||
| 321 | private static int phaseOf(long s) { | ||
| 322 | return (int)(s >>> PHASE_SHIFT); | ||
| 323 | } | ||
| 324 | |||
| 325 | private static int arrivedOf(long s) { | ||
| 326 | int counts = (int)s; | ||
| 327 | return (counts == EMPTY) ? 0 : | ||
| 328 | (counts >>> PARTIES_SHIFT) - (counts & UNARRIVED_MASK); | ||
| 329 | } | ||
| 330 | |||
| 331 | /** | ||
| 332 | * The parent of this phaser, or null if none | ||
| 333 | */ | ||
| 334 | private final Phaser parent; | ||
| 335 | |||
| 336 | /** | ||
| 337 | * The root of phaser tree. Equals this if not in a tree. | ||
| 338 | */ | ||
| 339 | private final Phaser root; | ||
| 340 | |||
| 341 | /** | ||
| 342 | * Heads of Treiber stacks for waiting threads. To eliminate | ||
| 343 | * contention when releasing some threads while adding others, we | ||
| 344 | * use two of them, alternating across even and odd phases. | ||
| 345 | * Subphasers share queues with root to speed up releases. | ||
| 346 | */ | ||
| 347 | private final AtomicReference<QNode> evenQ; | ||
| 348 | private final AtomicReference<QNode> oddQ; | ||
| 349 | |||
| 350 | private AtomicReference<QNode> queueFor(int phase) { | ||
| 351 | return ((phase & 1) == 0) ? evenQ : oddQ; | ||
| 352 | } | ||
| 353 | |||
| 354 | /** | ||
| 355 | * Returns message string for bounds exceptions on arrival. | ||
| 356 | */ | ||
| 357 | private String badArrive(long s) { | ||
| 358 | return "Attempted arrival of unregistered party for " + | ||
| 359 | stateToString(s); | ||
| 360 | } | ||
| 361 | |||
| 362 | /** | ||
| 363 | * Returns message string for bounds exceptions on registration. | ||
| 364 | */ | ||
| 365 | private String badRegister(long s) { | ||
| 366 | return "Attempt to register more than " + | ||
| 367 | MAX_PARTIES + " parties for " + stateToString(s); | ||
| 368 | } | ||
| 369 | |||
| 370 | /** | ||
| 371 | * Main implementation for methods arrive and arriveAndDeregister. | ||
| 372 | * Manually tuned to speed up and minimize race windows for the | ||
| 373 | * common case of just decrementing unarrived field. | ||
| 374 | * | ||
| 375 | * @param deregister false for arrive, true for arriveAndDeregister | ||
| 376 | */ | ||
| 377 | private int doArrive(boolean deregister) { | ||
| 378 | int adj = deregister ? ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL; | ||
| 379 | final Phaser root = this.root; | ||
| 380 | for (;;) { | ||
| 381 | long s = (root == this) ? state : reconcileState(); | ||
| 382 | int phase = (int)(s >>> PHASE_SHIFT); | ||
| 383 | int counts = (int)s; | ||
| 384 | int unarrived = (counts & UNARRIVED_MASK) - 1; | ||
| 385 | if (phase < 0) | ||
| 386 | return phase; | ||
| 387 | else if (counts == EMPTY || unarrived < 0) { | ||
| 388 | if (root == this || reconcileState() == s) | ||
| 389 | throw new IllegalStateException(badArrive(s)); | ||
| 390 | } | ||
| 391 | else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) { | ||
| 392 | if (unarrived == 0) { | ||
| 393 | long n = s & PARTIES_MASK; // base of next state | ||
| 394 | int nextUnarrived = (int)n >>> PARTIES_SHIFT; | ||
| 395 | if (root != this) | ||
| 396 | return parent.doArrive(nextUnarrived == 0); | ||
| 397 | if (onAdvance(phase, nextUnarrived)) | ||
| 398 | n |= TERMINATION_BIT; | ||
| 399 | else if (nextUnarrived == 0) | ||
| 400 | n |= EMPTY; | ||
| 401 | else | ||
| 402 | n |= nextUnarrived; | ||
| 403 | n |= (long)((phase + 1) & MAX_PHASE) << PHASE_SHIFT; | ||
| 404 | UNSAFE.compareAndSwapLong(this, stateOffset, s, n); | ||
| 405 | releaseWaiters(phase); | ||
| 406 | } | ||
| 407 | return phase; | ||
| 408 | } | ||
| 409 | } | ||
| 410 | } | ||
| 411 | |||
| 412 | /** | ||
| 413 | * Implementation of register, bulkRegister | ||
| 414 | * | ||
| 415 | * @param registrations number to add to both parties and | ||
| 416 | * unarrived fields. Must be greater than zero. | ||
| 417 | */ | ||
| 418 | private int doRegister(int registrations) { | ||
| 419 | // adjustment to state | ||
| 420 | long adj = ((long)registrations << PARTIES_SHIFT) | registrations; | ||
| 421 | final Phaser parent = this.parent; | ||
| 422 | int phase; | ||
| 423 | for (;;) { | ||
| 424 | long s = state; | ||
| 425 | int counts = (int)s; | ||
| 426 | int parties = counts >>> PARTIES_SHIFT; | ||
| 427 | int unarrived = counts & UNARRIVED_MASK; | ||
| 428 | if (registrations > MAX_PARTIES - parties) | ||
| 429 | throw new IllegalStateException(badRegister(s)); | ||
| 430 | else if ((phase = (int)(s >>> PHASE_SHIFT)) < 0) | ||
| 431 | break; | ||
| 432 | else if (counts != EMPTY) { // not 1st registration | ||
| 433 | if (parent == null || reconcileState() == s) { | ||
| 434 | if (unarrived == 0) // wait out advance | ||
| 435 | root.internalAwaitAdvance(phase, null); | ||
| 436 | else if (UNSAFE.compareAndSwapLong(this, stateOffset, | ||
| 437 | s, s + adj)) | ||
| 438 | break; | ||
| 439 | } | ||
| 440 | } | ||
| 441 | else if (parent == null) { // 1st root registration | ||
| 442 | long next = ((long)phase << PHASE_SHIFT) | adj; | ||
| 443 | if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) | ||
| 444 | break; | ||
| 445 | } | ||
| 446 | else { | ||
| 447 | synchronized (this) { // 1st sub registration | ||
| 448 | if (state == s) { // recheck under lock | ||
| 449 | parent.doRegister(1); | ||
| 450 | do { // force current phase | ||
| 451 | phase = (int)(root.state >>> PHASE_SHIFT); | ||
| 452 | // assert phase < 0 || (int)state == EMPTY; | ||
| 453 | } while (!UNSAFE.compareAndSwapLong | ||
| 454 | (this, stateOffset, state, | ||
| 455 | ((long)phase << PHASE_SHIFT) | adj)); | ||
| 456 | break; | ||
| 457 | } | ||
| 458 | } | ||
| 459 | } | ||
| 460 | } | ||
| 461 | return phase; | ||
| 462 | } | ||
| 463 | |||
| 464 | /** | ||
| 465 | * Resolves lagged phase propagation from root if necessary. | ||
| 466 | * Reconciliation normally occurs when root has advanced but | ||
| 467 | * subphasers have not yet done so, in which case they must finish | ||
| 468 | * their own advance by setting unarrived to parties (or if | ||
| 469 | * parties is zero, resetting to unregistered EMPTY state). | ||
| 470 | * However, this method may also be called when "floating" | ||
| 471 | * subphasers with possibly some unarrived parties are merely | ||
| 472 | * catching up to current phase, in which case counts are | ||
| 473 | * unaffected. | ||
| 474 | * | ||
| 475 | * @return reconciled state | ||
| 476 | */ | ||
| 477 | private long reconcileState() { | ||
| 478 | final Phaser root = this.root; | ||
| 479 | long s = state; | ||
| 480 | if (root != this) { | ||
| 481 | int phase, u, p; | ||
| 482 | // CAS root phase with current parties; possibly trip unarrived | ||
| 483 | while ((phase = (int)(root.state >>> PHASE_SHIFT)) != | ||
| 484 | (int)(s >>> PHASE_SHIFT) && | ||
| 485 | !UNSAFE.compareAndSwapLong | ||
| 486 | (this, stateOffset, s, | ||
| 487 | s = (((long)phase << PHASE_SHIFT) | | ||
| 488 | (s & PARTIES_MASK) | | ||
| 489 | ((p = (int)s >>> PARTIES_SHIFT) == 0 ? EMPTY : | ||
| 490 | (u = (int)s & UNARRIVED_MASK) == 0 ? p : u)))) | ||
| 491 | s = state; | ||
| 492 | } | ||
| 493 | return s; | ||
| 494 | } | ||
| 495 | |||
| 496 | /** | ||
| 497 | * Creates a new phaser with no initially registered parties, no | ||
| 498 | * parent, and initial phase number 0. Any thread using this | ||
| 499 | * phaser will need to first register for it. | ||
| 500 | */ | ||
| 501 | public Phaser() { | ||
| 502 | this(null, 0); | ||
| 503 | } | ||
| 504 | |||
| 505 | /** | ||
| 506 | * Creates a new phaser with the given number of registered | ||
| 507 | * unarrived parties, no parent, and initial phase number 0. | ||
| 508 | * | ||
| 509 | * @param parties the number of parties required to advance to the | ||
| 510 | * next phase | ||
| 511 | * @throws IllegalArgumentException if parties less than zero | ||
| 512 | * or greater than the maximum number of parties supported | ||
| 513 | */ | ||
| 514 | public Phaser(int parties) { | ||
| 515 | this(null, parties); | ||
| 516 | } | ||
| 517 | |||
| 518 | /** | ||
| 519 | * Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}. | ||
| 520 | * | ||
| 521 | * @param parent the parent phaser | ||
| 522 | */ | ||
| 523 | public Phaser(Phaser parent) { | ||
| 524 | this(parent, 0); | ||
| 525 | } | ||
| 526 | |||
| 527 | /** | ||
| 528 | * Creates a new phaser with the given parent and number of | ||
| 529 | * registered unarrived parties. When the given parent is non-null | ||
| 530 | * and the given number of parties is greater than zero, this | ||
| 531 | * child phaser is registered with its parent. | ||
| 532 | * | ||
| 533 | * @param parent the parent phaser | ||
| 534 | * @param parties the number of parties required to advance to the | ||
| 535 | * next phase | ||
| 536 | * @throws IllegalArgumentException if parties less than zero | ||
| 537 | * or greater than the maximum number of parties supported | ||
| 538 | */ | ||
| 539 | public Phaser(Phaser parent, int parties) { | ||
| 540 | if (parties >>> PARTIES_SHIFT != 0) | ||
| 541 | throw new IllegalArgumentException("Illegal number of parties"); | ||
| 542 | int phase = 0; | ||
| 543 | this.parent = parent; | ||
| 544 | if (parent != null) { | ||
| 545 | final Phaser root = parent.root; | ||
| 546 | this.root = root; | ||
| 547 | this.evenQ = root.evenQ; | ||
| 548 | this.oddQ = root.oddQ; | ||
| 549 | if (parties != 0) | ||
| 550 | phase = parent.doRegister(1); | ||
| 551 | } | ||
| 552 | else { | ||
| 553 | this.root = this; | ||
| 554 | this.evenQ = new AtomicReference<QNode>(); | ||
| 555 | this.oddQ = new AtomicReference<QNode>(); | ||
| 556 | } | ||
| 557 | this.state = (parties == 0) ? (long)EMPTY : | ||
| 558 | ((long)phase << PHASE_SHIFT) | | ||
| 559 | ((long)parties << PARTIES_SHIFT) | | ||
| 560 | ((long)parties); | ||
| 561 | } | ||
| 562 | |||
| 563 | /** | ||
| 564 | * Adds a new unarrived party to this phaser. If an ongoing | ||
| 565 | * invocation of {@link #onAdvance} is in progress, this method | ||
| 566 | * may await its completion before returning. If this phaser has | ||
| 567 | * a parent, and this phaser previously had no registered parties, | ||
| 568 | * this child phaser is also registered with its parent. If | ||
| 569 | * this phaser is terminated, the attempt to register has | ||
| 570 | * no effect, and a negative value is returned. | ||
| 571 | * | ||
| 572 | * @return the arrival phase number to which this registration | ||
| 573 | * applied. If this value is negative, then this phaser has | ||
| 574 | * terminated, in which case registration has no effect. | ||
| 575 | * @throws IllegalStateException if attempting to register more | ||
| 576 | * than the maximum supported number of parties | ||
| 577 | */ | ||
| 578 | public int register() { | ||
| 579 | return doRegister(1); | ||
| 580 | } | ||
| 581 | |||
| 582 | /** | ||
| 583 | * Adds the given number of new unarrived parties to this phaser. | ||
| 584 | * If an ongoing invocation of {@link #onAdvance} is in progress, | ||
| 585 | * this method may await its completion before returning. If this | ||
| 586 | * phaser has a parent, and the given number of parties is greater | ||
| 587 | * than zero, and this phaser previously had no registered | ||
| 588 | * parties, this child phaser is also registered with its parent. | ||
| 589 | * If this phaser is terminated, the attempt to register has no | ||
| 590 | * effect, and a negative value is returned. | ||
| 591 | * | ||
| 592 | * @param parties the number of additional parties required to | ||
| 593 | * advance to the next phase | ||
| 594 | * @return the arrival phase number to which this registration | ||
| 595 | * applied. If this value is negative, then this phaser has | ||
| 596 | * terminated, in which case registration has no effect. | ||
| 597 | * @throws IllegalStateException if attempting to register more | ||
| 598 | * than the maximum supported number of parties | ||
| 599 | * @throws IllegalArgumentException if {@code parties < 0} | ||
| 600 | */ | ||
| 601 | public int bulkRegister(int parties) { | ||
| 602 | if (parties < 0) | ||
| 603 | throw new IllegalArgumentException(); | ||
| 604 | if (parties == 0) | ||
| 605 | return getPhase(); | ||
| 606 | return doRegister(parties); | ||
| 607 | } | ||
| 608 | |||
| 609 | /** | ||
| 610 | * Arrives at this phaser, without waiting for others to arrive. | ||
| 611 | * | ||
| 612 | * <p>It is a usage error for an unregistered party to invoke this | ||
| 613 | * method. However, this error may result in an {@code | ||
| 614 | * IllegalStateException} only upon some subsequent operation on | ||
| 615 | * this phaser, if ever. | ||
| 616 | * | ||
| 617 | * @return the arrival phase number, or a negative value if terminated | ||
| 618 | * @throws IllegalStateException if not terminated and the number | ||
| 619 | * of unarrived parties would become negative | ||
| 620 | */ | ||
| 621 | public int arrive() { | ||
| 622 | return doArrive(false); | ||
| 623 | } | ||
| 624 | |||
| 625 | /** | ||
| 626 | * Arrives at this phaser and deregisters from it without waiting | ||
| 627 | * for others to arrive. Deregistration reduces the number of | ||
| 628 | * parties required to advance in future phases. If this phaser | ||
| 629 | * has a parent, and deregistration causes this phaser to have | ||
| 630 | * zero parties, this phaser is also deregistered from its parent. | ||
| 631 | * | ||
| 632 | * <p>It is a usage error for an unregistered party to invoke this | ||
| 633 | * method. However, this error may result in an {@code | ||
| 634 | * IllegalStateException} only upon some subsequent operation on | ||
| 635 | * this phaser, if ever. | ||
| 636 | * | ||
| 637 | * @return the arrival phase number, or a negative value if terminated | ||
| 638 | * @throws IllegalStateException if not terminated and the number | ||
| 639 | * of registered or unarrived parties would become negative | ||
| 640 | */ | ||
| 641 | public int arriveAndDeregister() { | ||
| 642 | return doArrive(true); | ||
| 643 | } | ||
| 644 | |||
| 645 | /** | ||
| 646 | * Arrives at this phaser and awaits others. Equivalent in effect | ||
| 647 | * to {@code awaitAdvance(arrive())}. If you need to await with | ||
| 648 | * interruption or timeout, you can arrange this with an analogous | ||
| 649 | * construction using one of the other forms of the {@code | ||
| 650 | * awaitAdvance} method. If instead you need to deregister upon | ||
| 651 | * arrival, use {@code awaitAdvance(arriveAndDeregister())}. | ||
| 652 | * | ||
| 653 | * <p>It is a usage error for an unregistered party to invoke this | ||
| 654 | * method. However, this error may result in an {@code | ||
| 655 | * IllegalStateException} only upon some subsequent operation on | ||
| 656 | * this phaser, if ever. | ||
| 657 | * | ||
| 658 | * @return the arrival phase number, or the (negative) | ||
| 659 | * {@linkplain #getPhase() current phase} if terminated | ||
| 660 | * @throws IllegalStateException if not terminated and the number | ||
| 661 | * of unarrived parties would become negative | ||
| 662 | */ | ||
| 663 | public int arriveAndAwaitAdvance() { | ||
| 664 | // Specialization of doArrive+awaitAdvance eliminating some reads/paths | ||
| 665 | final Phaser root = this.root; | ||
| 666 | for (;;) { | ||
| 667 | long s = (root == this) ? state : reconcileState(); | ||
| 668 | int phase = (int)(s >>> PHASE_SHIFT); | ||
| 669 | int counts = (int)s; | ||
| 670 | int unarrived = (counts & UNARRIVED_MASK) - 1; | ||
| 671 | if (phase < 0) | ||
| 672 | return phase; | ||
| 673 | else if (counts == EMPTY || unarrived < 0) { | ||
| 674 | if (reconcileState() == s) | ||
| 675 | throw new IllegalStateException(badArrive(s)); | ||
| 676 | } | ||
| 677 | else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, | ||
| 678 | s -= ONE_ARRIVAL)) { | ||
| 679 | if (unarrived != 0) | ||
| 680 | return root.internalAwaitAdvance(phase, null); | ||
| 681 | if (root != this) | ||
| 682 | return parent.arriveAndAwaitAdvance(); | ||
| 683 | long n = s & PARTIES_MASK; // base of next state | ||
| 684 | int nextUnarrived = (int)n >>> PARTIES_SHIFT; | ||
| 685 | if (onAdvance(phase, nextUnarrived)) | ||
| 686 | n |= TERMINATION_BIT; | ||
| 687 | else if (nextUnarrived == 0) | ||
| 688 | n |= EMPTY; | ||
| 689 | else | ||
| 690 | n |= nextUnarrived; | ||
| 691 | int nextPhase = (phase + 1) & MAX_PHASE; | ||
| 692 | n |= (long)nextPhase << PHASE_SHIFT; | ||
| 693 | if (!UNSAFE.compareAndSwapLong(this, stateOffset, s, n)) | ||
| 694 | return (int)(state >>> PHASE_SHIFT); // terminated | ||
| 695 | releaseWaiters(phase); | ||
| 696 | return nextPhase; | ||
| 697 | } | ||
| 698 | } | ||
| 699 | } | ||
| 700 | |||
| 701 | /** | ||
| 702 | * Awaits the phase of this phaser to advance from the given phase | ||
| 703 | * value, returning immediately if the current phase is not equal | ||
| 704 | * to the given phase value or this phaser is terminated. | ||
| 705 | * | ||
| 706 | * @param phase an arrival phase number, or negative value if | ||
| 707 | * terminated; this argument is normally the value returned by a | ||
| 708 | * previous call to {@code arrive} or {@code arriveAndDeregister}. | ||
| 709 | * @return the next arrival phase number, or the argument if it is | ||
| 710 | * negative, or the (negative) {@linkplain #getPhase() current phase} | ||
| 711 | * if terminated | ||
| 712 | */ | ||
| 713 | public int awaitAdvance(int phase) { | ||
| 714 | final Phaser root = this.root; | ||
| 715 | long s = (root == this) ? state : reconcileState(); | ||
| 716 | int p = (int)(s >>> PHASE_SHIFT); | ||
| 717 | if (phase < 0) | ||
| 718 | return phase; | ||
| 719 | if (p == phase) | ||
| 720 | return root.internalAwaitAdvance(phase, null); | ||
| 721 | return p; | ||
| 722 | } | ||
| 723 | |||
| 724 | /** | ||
| 725 | * Awaits the phase of this phaser to advance from the given phase | ||
| 726 | * value, throwing {@code InterruptedException} if interrupted | ||
| 727 | * while waiting, or returning immediately if the current phase is | ||
| 728 | * not equal to the given phase value or this phaser is | ||
| 729 | * terminated. | ||
| 730 | * | ||
| 731 | * @param phase an arrival phase number, or negative value if | ||
| 732 | * terminated; this argument is normally the value returned by a | ||
| 733 | * previous call to {@code arrive} or {@code arriveAndDeregister}. | ||
| 734 | * @return the next arrival phase number, or the argument if it is | ||
| 735 | * negative, or the (negative) {@linkplain #getPhase() current phase} | ||
| 736 | * if terminated | ||
| 737 | * @throws InterruptedException if thread interrupted while waiting | ||
| 738 | */ | ||
| 739 | public int awaitAdvanceInterruptibly(int phase) | ||
| 740 | throws InterruptedException { | ||
| 741 | final Phaser root = this.root; | ||
| 742 | long s = (root == this) ? state : reconcileState(); | ||
| 743 | int p = (int)(s >>> PHASE_SHIFT); | ||
| 744 | if (phase < 0) | ||
| 745 | return phase; | ||
| 746 | if (p == phase) { | ||
| 747 | QNode node = new QNode(this, phase, true, false, 0L); | ||
| 748 | p = root.internalAwaitAdvance(phase, node); | ||
| 749 | if (node.wasInterrupted) | ||
| 750 | throw new InterruptedException(); | ||
| 751 | } | ||
| 752 | return p; | ||
| 753 | } | ||
| 754 | |||
| 755 | /** | ||
| 756 | * Awaits the phase of this phaser to advance from the given phase | ||
| 757 | * value or the given timeout to elapse, throwing {@code | ||
| 758 | * InterruptedException} if interrupted while waiting, or | ||
| 759 | * returning immediately if the current phase is not equal to the | ||
| 760 | * given phase value or this phaser is terminated. | ||
| 761 | * | ||
| 762 | * @param phase an arrival phase number, or negative value if | ||
| 763 | * terminated; this argument is normally the value returned by a | ||
| 764 | * previous call to {@code arrive} or {@code arriveAndDeregister}. | ||
| 765 | * @param timeout how long to wait before giving up, in units of | ||
| 766 | * {@code unit} | ||
| 767 | * @param unit a {@code TimeUnit} determining how to interpret the | ||
| 768 | * {@code timeout} parameter | ||
| 769 | * @return the next arrival phase number, or the argument if it is | ||
| 770 | * negative, or the (negative) {@linkplain #getPhase() current phase} | ||
| 771 | * if terminated | ||
| 772 | * @throws InterruptedException if thread interrupted while waiting | ||
| 773 | * @throws TimeoutException if timed out while waiting | ||
| 774 | */ | ||
| 775 | public int awaitAdvanceInterruptibly(int phase, | ||
| 776 | long timeout, TimeUnit unit) | ||
| 777 | throws InterruptedException, TimeoutException { | ||
| 778 | long nanos = unit.toNanos(timeout); | ||
| 779 | final Phaser root = this.root; | ||
| 780 | long s = (root == this) ? state : reconcileState(); | ||
| 781 | int p = (int)(s >>> PHASE_SHIFT); | ||
| 782 | if (phase < 0) | ||
| 783 | return phase; | ||
| 784 | if (p == phase) { | ||
| 785 | QNode node = new QNode(this, phase, true, true, nanos); | ||
| 786 | p = root.internalAwaitAdvance(phase, node); | ||
| 787 | if (node.wasInterrupted) | ||
| 788 | throw new InterruptedException(); | ||
| 789 | else if (p == phase) | ||
| 790 | throw new TimeoutException(); | ||
| 791 | } | ||
| 792 | return p; | ||
| 793 | } | ||
| 794 | |||
| 795 | /** | ||
| 796 | * Forces this phaser to enter termination state. Counts of | ||
| 797 | * registered parties are unaffected. If this phaser is a member | ||
| 798 | * of a tiered set of phasers, then all of the phasers in the set | ||
| 799 | * are terminated. If this phaser is already terminated, this | ||
| 800 | * method has no effect. This method may be useful for | ||
| 801 | * coordinating recovery after one or more tasks encounter | ||
| 802 | * unexpected exceptions. | ||
| 803 | */ | ||
| 804 | public void forceTermination() { | ||
| 805 | // Only need to change root state | ||
| 806 | final Phaser root = this.root; | ||
| 807 | long s; | ||
| 808 | while ((s = root.state) >= 0) { | ||
| 809 | if (UNSAFE.compareAndSwapLong(root, stateOffset, | ||
| 810 | s, s | TERMINATION_BIT)) { | ||
| 811 | // signal all threads | ||
| 812 | releaseWaiters(0); | ||
| 813 | releaseWaiters(1); | ||
| 814 | return; | ||
| 815 | } | ||
| 816 | } | ||
| 817 | } | ||
| 818 | |||
| 819 | /** | ||
| 820 | * Returns the current phase number. The maximum phase number is | ||
| 821 | * {@code Integer.MAX_VALUE}, after which it restarts at | ||
| 822 | * zero. Upon termination, the phase number is negative, | ||
| 823 | * in which case the prevailing phase prior to termination | ||
| 824 | * may be obtained via {@code getPhase() + Integer.MIN_VALUE}. | ||
| 825 | * | ||
| 826 | * @return the phase number, or a negative value if terminated | ||
| 827 | */ | ||
| 828 | public final int getPhase() { | ||
| 829 | return (int)(root.state >>> PHASE_SHIFT); | ||
| 830 | } | ||
| 831 | |||
| 832 | /** | ||
| 833 | * Returns the number of parties registered at this phaser. | ||
| 834 | * | ||
| 835 | * @return the number of parties | ||
| 836 | */ | ||
| 837 | public int getRegisteredParties() { | ||
| 838 | return partiesOf(state); | ||
| 839 | } | ||
| 840 | |||
| 841 | /** | ||
| 842 | * Returns the number of registered parties that have arrived at | ||
| 843 | * the current phase of this phaser. If this phaser has terminated, | ||
| 844 | * the returned value is meaningless and arbitrary. | ||
| 845 | * | ||
| 846 | * @return the number of arrived parties | ||
| 847 | */ | ||
| 848 | public int getArrivedParties() { | ||
| 849 | return arrivedOf(reconcileState()); | ||
| 850 | } | ||
| 851 | |||
| 852 | /** | ||
| 853 | * Returns the number of registered parties that have not yet | ||
| 854 | * arrived at the current phase of this phaser. If this phaser has | ||
| 855 | * terminated, the returned value is meaningless and arbitrary. | ||
| 856 | * | ||
| 857 | * @return the number of unarrived parties | ||
| 858 | */ | ||
| 859 | public int getUnarrivedParties() { | ||
| 860 | return unarrivedOf(reconcileState()); | ||
| 861 | } | ||
| 862 | |||
| 863 | /** | ||
| 864 | * Returns the parent of this phaser, or {@code null} if none. | ||
| 865 | * | ||
| 866 | * @return the parent of this phaser, or {@code null} if none | ||
| 867 | */ | ||
| 868 | public Phaser getParent() { | ||
| 869 | return parent; | ||
| 870 | } | ||
| 871 | |||
| 872 | /** | ||
| 873 | * Returns the root ancestor of this phaser, which is the same as | ||
| 874 | * this phaser if it has no parent. | ||
| 875 | * | ||
| 876 | * @return the root ancestor of this phaser | ||
| 877 | */ | ||
| 878 | public Phaser getRoot() { | ||
| 879 | return root; | ||
| 880 | } | ||
| 881 | |||
| 882 | /** | ||
| 883 | * Returns {@code true} if this phaser has been terminated. | ||
| 884 | * | ||
| 885 | * @return {@code true} if this phaser has been terminated | ||
| 886 | */ | ||
| 887 | public boolean isTerminated() { | ||
| 888 | return root.state < 0L; | ||
| 889 | } | ||
| 890 | |||
| 891 | /** | ||
| 892 | * Overridable method to perform an action upon impending phase | ||
| 893 | * advance, and to control termination. This method is invoked | ||
| 894 | * upon arrival of the party advancing this phaser (when all other | ||
| 895 | * waiting parties are dormant). If this method returns {@code | ||
| 896 | * true}, this phaser will be set to a final termination state | ||
| 897 | * upon advance, and subsequent calls to {@link #isTerminated} | ||
| 898 | * will return true. Any (unchecked) Exception or Error thrown by | ||
| 899 | * an invocation of this method is propagated to the party | ||
| 900 | * attempting to advance this phaser, in which case no advance | ||
| 901 | * occurs. | ||
| 902 | * | ||
| 903 | * <p>The arguments to this method provide the state of the phaser | ||
| 904 | * prevailing for the current transition. The effects of invoking | ||
| 905 | * arrival, registration, and waiting methods on this phaser from | ||
| 906 | * within {@code onAdvance} are unspecified and should not be | ||
| 907 | * relied on. | ||
| 908 | * | ||
| 909 | * <p>If this phaser is a member of a tiered set of phasers, then | ||
| 910 | * {@code onAdvance} is invoked only for its root phaser on each | ||
| 911 | * advance. | ||
| 912 | * | ||
| 913 | * <p>To support the most common use cases, the default | ||
| 914 | * implementation of this method returns {@code true} when the | ||
| 915 | * number of registered parties has become zero as the result of a | ||
| 916 | * party invoking {@code arriveAndDeregister}. You can disable | ||
| 917 | * this behavior, thus enabling continuation upon future | ||
| 918 | * registrations, by overriding this method to always return | ||
| 919 | * {@code false}: | ||
| 920 | * | ||
| 921 | * <pre> {@code | ||
| 922 | * Phaser phaser = new Phaser() { | ||
| 923 | * protected boolean onAdvance(int phase, int parties) { return false; } | ||
| 924 | * }}</pre> | ||
| 925 | * | ||
| 926 | * @param phase the current phase number on entry to this method, | ||
| 927 | * before this phaser is advanced | ||
| 928 | * @param registeredParties the current number of registered parties | ||
| 929 | * @return {@code true} if this phaser should terminate | ||
| 930 | */ | ||
| 931 | protected boolean onAdvance(int phase, int registeredParties) { | ||
| 932 | return registeredParties == 0; | ||
| 933 | } | ||
| 934 | |||
| 935 | /** | ||
| 936 | * Returns a string identifying this phaser, as well as its | ||
| 937 | * state. The state, in brackets, includes the String {@code | ||
| 938 | * "phase = "} followed by the phase number, {@code "parties = "} | ||
| 939 | * followed by the number of registered parties, and {@code | ||
| 940 | * "arrived = "} followed by the number of arrived parties. | ||
| 941 | * | ||
| 942 | * @return a string identifying this phaser, as well as its state | ||
| 943 | */ | ||
| 944 | public String toString() { | ||
| 945 | return stateToString(reconcileState()); | ||
| 946 | } | ||
| 947 | |||
| 948 | /** | ||
| 949 | * Implementation of toString and string-based error messages | ||
| 950 | */ | ||
| 951 | private String stateToString(long s) { | ||
| 952 | return super.toString() + | ||
| 953 | "[phase = " + phaseOf(s) + | ||
| 954 | " parties = " + partiesOf(s) + | ||
| 955 | " arrived = " + arrivedOf(s) + "]"; | ||
| 956 | } | ||
| 957 | |||
| 958 | // Waiting mechanics | ||
| 959 | |||
| 960 | /** | ||
| 961 | * Removes and signals threads from queue for phase. | ||
| 962 | */ | ||
| 963 | private void releaseWaiters(int phase) { | ||
| 964 | QNode q; // first element of queue | ||
| 965 | Thread t; // its thread | ||
| 966 | AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; | ||
| 967 | while ((q = head.get()) != null && | ||
| 968 | q.phase != (int)(root.state >>> PHASE_SHIFT)) { | ||
| 969 | if (head.compareAndSet(q, q.next) && | ||
| 970 | (t = q.thread) != null) { | ||
| 971 | q.thread = null; | ||
| 972 | LockSupport.unpark(t); | ||
| 973 | } | ||
| 974 | } | ||
| 975 | } | ||
| 976 | |||
| 977 | /** | ||
| 978 | * Variant of releaseWaiters that additionally tries to remove any | ||
| 979 | * nodes no longer waiting for advance due to timeout or | ||
| 980 | * interrupt. Currently, nodes are removed only if they are at | ||
| 981 | * head of queue, which suffices to reduce memory footprint in | ||
| 982 | * most usages. | ||
| 983 | * | ||
| 984 | * @return current phase on exit | ||
| 985 | */ | ||
| 986 | private int abortWait(int phase) { | ||
| 987 | AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; | ||
| 988 | for (;;) { | ||
| 989 | Thread t; | ||
| 990 | QNode q = head.get(); | ||
| 991 | int p = (int)(root.state >>> PHASE_SHIFT); | ||
| 992 | if (q == null || ((t = q.thread) != null && q.phase == p)) | ||
| 993 | return p; | ||
| 994 | if (head.compareAndSet(q, q.next) && t != null) { | ||
| 995 | q.thread = null; | ||
| 996 | LockSupport.unpark(t); | ||
| 997 | } | ||
| 998 | } | ||
| 999 | } | ||
| 1000 | |||
| 1001 | /** The number of CPUs, for spin control */ | ||
| 1002 | private static final int NCPU = Runtime.getRuntime().availableProcessors(); | ||
| 1003 | |||
| 1004 | /** | ||
| 1005 | * The number of times to spin before blocking while waiting for | ||
| 1006 | * advance, per arrival while waiting. On multiprocessors, fully | ||
| 1007 | * blocking and waking up a large number of threads all at once is | ||
| 1008 | * usually a very slow process, so we use rechargeable spins to | ||
| 1009 | * avoid it when threads regularly arrive: When a thread in | ||
| 1010 | * internalAwaitAdvance notices another arrival before blocking, | ||
| 1011 | * and there appear to be enough CPUs available, it spins | ||
| 1012 | * SPINS_PER_ARRIVAL more times before blocking. The value trades | ||
| 1013 | * off good-citizenship vs big unnecessary slowdowns. | ||
| 1014 | */ | ||
| 1015 | static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8; | ||
| 1016 | |||
| 1017 | /** | ||
| 1018 | * Possibly blocks and waits for phase to advance unless aborted. | ||
| 1019 | * Call only from root node. | ||
| 1020 | * | ||
| 1021 | * @param phase current phase | ||
| 1022 | * @param node if non-null, the wait node to track interrupt and timeout; | ||
| 1023 | * if null, denotes noninterruptible wait | ||
| 1024 | * @return current phase | ||
| 1025 | */ | ||
| 1026 | private int internalAwaitAdvance(int phase, QNode node) { | ||
| 1027 | releaseWaiters(phase-1); // ensure old queue clean | ||
| 1028 | boolean queued = false; // true when node is enqueued | ||
| 1029 | int lastUnarrived = 0; // to increase spins upon change | ||
| 1030 | int spins = SPINS_PER_ARRIVAL; | ||
| 1031 | long s; | ||
| 1032 | int p; | ||
| 1033 | while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) { | ||
| 1034 | if (node == null) { // spinning in noninterruptible mode | ||
| 1035 | int unarrived = (int)s & UNARRIVED_MASK; | ||
| 1036 | if (unarrived != lastUnarrived && | ||
| 1037 | (lastUnarrived = unarrived) < NCPU) | ||
| 1038 | spins += SPINS_PER_ARRIVAL; | ||
| 1039 | boolean interrupted = Thread.interrupted(); | ||
| 1040 | if (interrupted || --spins < 0) { // need node to record intr | ||
| 1041 | node = new QNode(this, phase, false, false, 0L); | ||
| 1042 | node.wasInterrupted = interrupted; | ||
| 1043 | } | ||
| 1044 | } | ||
| 1045 | else if (node.isReleasable()) // done or aborted | ||
| 1046 | break; | ||
| 1047 | else if (!queued) { // push onto queue | ||
| 1048 | AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; | ||
| 1049 | QNode q = node.next = head.get(); | ||
| 1050 | if ((q == null || q.phase == phase) && | ||
| 1051 | (int)(state >>> PHASE_SHIFT) == phase) // avoid stale enq | ||
| 1052 | queued = head.compareAndSet(q, node); | ||
| 1053 | } | ||
| 1054 | else { | ||
| 1055 | try { | ||
| 1056 | ForkJoinPool.managedBlock(node); | ||
| 1057 | } catch (InterruptedException ie) { | ||
| 1058 | node.wasInterrupted = true; | ||
| 1059 | } | ||
| 1060 | } | ||
| 1061 | } | ||
| 1062 | |||
| 1063 | if (node != null) { | ||
| 1064 | if (node.thread != null) | ||
| 1065 | node.thread = null; // avoid need for unpark() | ||
| 1066 | if (node.wasInterrupted && !node.interruptible) | ||
| 1067 | Thread.currentThread().interrupt(); | ||
| 1068 | if (p == phase && (p = (int)(state >>> PHASE_SHIFT)) == phase) | ||
| 1069 | return abortWait(phase); // possibly clean up on abort | ||
| 1070 | } | ||
| 1071 | releaseWaiters(phase); | ||
| 1072 | return p; | ||
| 1073 | } | ||
| 1074 | |||
| 1075 | /** | ||
| 1076 | * Wait nodes for Treiber stack representing wait queue | ||
| 1077 | */ | ||
| 1078 | static final class QNode implements ForkJoinPool.ManagedBlocker { | ||
| 1079 | final Phaser phaser; | ||
| 1080 | final int phase; | ||
| 1081 | final boolean interruptible; | ||
| 1082 | final boolean timed; | ||
| 1083 | boolean wasInterrupted; | ||
| 1084 | long nanos; | ||
| 1085 | long lastTime; | ||
| 1086 | volatile Thread thread; // nulled to cancel wait | ||
| 1087 | QNode next; | ||
| 1088 | |||
| 1089 | QNode(Phaser phaser, int phase, boolean interruptible, | ||
| 1090 | boolean timed, long nanos) { | ||
| 1091 | this.phaser = phaser; | ||
| 1092 | this.phase = phase; | ||
| 1093 | this.interruptible = interruptible; | ||
| 1094 | this.nanos = nanos; | ||
| 1095 | this.timed = timed; | ||
| 1096 | this.lastTime = timed ? System.nanoTime() : 0L; | ||
| 1097 | thread = Thread.currentThread(); | ||
| 1098 | } | ||
| 1099 | |||
| 1100 | public boolean isReleasable() { | ||
| 1101 | if (thread == null) | ||
| 1102 | return true; | ||
| 1103 | if (phaser.getPhase() != phase) { | ||
| 1104 | thread = null; | ||
| 1105 | return true; | ||
| 1106 | } | ||
| 1107 | if (Thread.interrupted()) | ||
| 1108 | wasInterrupted = true; | ||
| 1109 | if (wasInterrupted && interruptible) { | ||
| 1110 | thread = null; | ||
| 1111 | return true; | ||
| 1112 | } | ||
| 1113 | if (timed) { | ||
| 1114 | if (nanos > 0L) { | ||
| 1115 | long now = System.nanoTime(); | ||
| 1116 | nanos -= now - lastTime; | ||
| 1117 | lastTime = now; | ||
| 1118 | } | ||
| 1119 | if (nanos <= 0L) { | ||
| 1120 | thread = null; | ||
| 1121 | return true; | ||
| 1122 | } | ||
| 1123 | } | ||
| 1124 | return false; | ||
| 1125 | } | ||
| 1126 | |||
| 1127 | public boolean block() { | ||
| 1128 | if (isReleasable()) | ||
| 1129 | return true; | ||
| 1130 | else if (!timed) | ||
| 1131 | LockSupport.park(this); | ||
| 1132 | else if (nanos > 0) | ||
| 1133 | LockSupport.parkNanos(this, nanos); | ||
| 1134 | return isReleasable(); | ||
| 1135 | } | ||
| 1136 | } | ||
| 1137 | |||
| 1138 | // Unsafe mechanics | ||
| 1139 | |||
| 1140 | private static final sun.misc.Unsafe UNSAFE; | ||
| 1141 | private static final long stateOffset; | ||
| 1142 | static { | ||
| 1143 | try { | ||
| 1144 | UNSAFE = sun.misc.Unsafe.getUnsafe(); | ||
| 1145 | Class k = Phaser.class; | ||
| 1146 | stateOffset = UNSAFE.objectFieldOffset | ||
| 1147 | (k.getDeclaredField("state")); | ||
| 1148 | } catch (Exception e) { | ||
| 1149 | throw new Error(e); | ||
| 1150 | } | ||
| 1151 | } | ||
| 1152 | } | ||