| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.util.concurrent.atomic.AtomicReference; |
| import java.util.concurrent.locks.LockSupport; |
| |
| /** |
| * A reusable synchronization barrier, similar in functionality to |
| * {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and |
| * {@link java.util.concurrent.CountDownLatch CountDownLatch} |
| * but supporting more flexible usage. |
| * |
| * <p><b>Registration.</b> Unlike the case for other barriers, the |
| * number of parties <em>registered</em> to synchronize on a phaser |
| * may vary over time. Tasks may be registered at any time (using |
| * methods {@link #register}, {@link #bulkRegister}, or forms of |
| * constructors establishing initial numbers of parties), and |
| * optionally deregistered upon any arrival (using {@link |
| * #arriveAndDeregister}). As is the case with most basic |
| * synchronization constructs, registration and deregistration affect |
| * only internal counts; they do not establish any further internal |
| * bookkeeping, so tasks cannot query whether they are registered. |
| * (However, you can introduce such bookkeeping by subclassing this |
| * class.) |
| * |
| * <p><b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code |
| * Phaser} may be repeatedly awaited. Method {@link |
| * #arriveAndAwaitAdvance} has effect analogous to {@link |
| * java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each |
| * generation of a phaser has an associated phase number. The phase |
| * number starts at zero, and advances when all parties arrive at the |
| * phaser, wrapping around to zero after reaching {@code |
| * Integer.MAX_VALUE}. The use of phase numbers enables independent |
| * control of actions upon arrival at a phaser and upon awaiting |
| * others, via two kinds of methods that may be invoked by any |
| * registered party: |
| * |
| * <ul> |
| * |
| * <li><b>Arrival.</b> Methods {@link #arrive} and |
| * {@link #arriveAndDeregister} record arrival. These methods |
| * do not block, but return an associated <em>arrival phase |
| * number</em>; that is, the phase number of the phaser to which |
| * the arrival applied. When the final party for a given phase |
| * arrives, an optional action is performed and the phase |
| * advances. These actions are performed by the party |
| * triggering a phase advance, and are arranged by overriding |
| * method {@link #onAdvance(int, int)}, which also controls |
| * termination. Overriding this method is similar to, but more |
| * flexible than, providing a barrier action to a {@code |
| * CyclicBarrier}. |
| * |
| * <li><b>Waiting.</b> Method {@link #awaitAdvance} requires an |
| * argument indicating an arrival phase number, and returns when |
| * the phaser advances to (or is already at) a different phase. |
| * Unlike similar constructions using {@code CyclicBarrier}, |
| * method {@code awaitAdvance} continues to wait even if the |
| * waiting thread is interrupted. Interruptible and timeout |
| * versions are also available, but exceptions encountered while |
| * tasks wait interruptibly or with timeout do not change the |
| * state of the phaser. If necessary, you can perform any |
| * associated recovery within handlers of those exceptions, |
| * often after invoking {@code forceTermination}. Phasers may |
| * also be used by tasks executing in a {@link ForkJoinPool}. |
| * Progress is ensured if the pool's parallelismLevel can |
| * accommodate the maximum number of simultaneously blocked |
| * parties. |
| * |
| * </ul> |
| * |
| * <p><b>Termination.</b> A phaser may enter a <em>termination</em> |
| * state, that may be checked using method {@link #isTerminated}. Upon |
| * termination, all synchronization methods immediately return without |
| * waiting for advance, as indicated by a negative return value. |
| * Similarly, attempts to register upon termination have no effect. |
| * Termination is triggered when an invocation of {@code onAdvance} |
| * returns {@code true}. The default implementation returns {@code |
| * true} if a deregistration has caused the number of registered |
| * parties to become zero. As illustrated below, when phasers control |
| * actions with a fixed number of iterations, it is often convenient |
| * to override this method to cause termination when the current phase |
| * number reaches a threshold. Method {@link #forceTermination} is |
| * also available to abruptly release waiting threads and allow them |
| * to terminate. |
| * |
| * <p><b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., |
| * constructed in tree structures) to reduce contention. Phasers with |
| * large numbers of parties that would otherwise experience heavy |
| * synchronization contention costs may instead be set up so that |
| * groups of sub-phasers share a common parent. This may greatly |
| * increase throughput even though it incurs greater per-operation |
| * overhead. |
| * |
| * <p>In a tree of tiered phasers, registration and deregistration of |
| * child phasers with their parent are managed automatically. |
| * Whenever the number of registered parties of a child phaser becomes |
| * non-zero (as established in the {@link #Phaser(Phaser,int)} |
| * constructor, {@link #register}, or {@link #bulkRegister}), the |
| * child phaser is registered with its parent. Whenever the number of |
| * registered parties becomes zero as the result of an invocation of |
| * {@link #arriveAndDeregister}, the child phaser is deregistered |
| * from its parent. |
| * |
| * <p><b>Monitoring.</b> While synchronization methods may be invoked |
| * only by registered parties, the current state of a phaser may be |
| * monitored by any caller. At any given moment there are {@link |
| * #getRegisteredParties} parties in total, of which {@link |
| * #getArrivedParties} have arrived at the current phase ({@link |
| * #getPhase}). When the remaining ({@link #getUnarrivedParties}) |
| * parties arrive, the phase advances. The values returned by these |
| * methods may reflect transient states and so are not in general |
| * useful for synchronization control. Method {@link #toString} |
| * returns snapshots of these state queries in a form convenient for |
| * informal monitoring. |
| * |
| * <p><b>Sample usages:</b> |
| * |
| * <p>A {@code Phaser} may be used instead of a {@code CountDownLatch} |
| * to control a one-shot action serving a variable number of parties. |
| * The typical idiom is for the method setting this up to first |
| * register, then start the actions, then deregister, as in: |
| * |
| * <pre> {@code |
| * void runTasks(List<Runnable> tasks) { |
| * final Phaser phaser = new Phaser(1); // "1" to register self |
| * // create and start threads |
| * for (final Runnable task : tasks) { |
| * phaser.register(); |
| * new Thread() { |
| * public void run() { |
| * phaser.arriveAndAwaitAdvance(); // await all creation |
| * task.run(); |
| * } |
| * }.start(); |
| * } |
| * |
| * // allow threads to start and deregister self |
| * phaser.arriveAndDeregister(); |
| * }}</pre> |
| * |
| * <p>One way to cause a set of threads to repeatedly perform actions |
| * for a given number of iterations is to override {@code onAdvance}: |
| * |
| * <pre> {@code |
| * void startTasks(List<Runnable> tasks, final int iterations) { |
| * final Phaser phaser = new Phaser() { |
| * protected boolean onAdvance(int phase, int registeredParties) { |
| * return phase >= iterations || registeredParties == 0; |
| * } |
| * }; |
| * phaser.register(); |
| * for (final Runnable task : tasks) { |
| * phaser.register(); |
| * new Thread() { |
| * public void run() { |
| * do { |
| * task.run(); |
| * phaser.arriveAndAwaitAdvance(); |
| * } while (!phaser.isTerminated()); |
| * } |
| * }.start(); |
| * } |
| * phaser.arriveAndDeregister(); // deregister self, don't wait |
| * }}</pre> |
| * |
| * If the main task must later await termination, it |
| * may re-register and then execute a similar loop: |
| * <pre> {@code |
| * // ... |
| * phaser.register(); |
| * while (!phaser.isTerminated()) |
| * phaser.arriveAndAwaitAdvance();}</pre> |
| * |
| * <p>Related constructions may be used to await particular phase numbers |
| * in contexts where you are sure that the phase will never wrap around |
| * {@code Integer.MAX_VALUE}. For example: |
| * |
| * <pre> {@code |
| * void awaitPhase(Phaser phaser, int phase) { |
| * int p = phaser.register(); // assumes caller not already registered |
| * while (p < phase) { |
| * if (phaser.isTerminated()) |
| * // ... deal with unexpected termination |
| * else |
| * p = phaser.arriveAndAwaitAdvance(); |
| * } |
| * phaser.arriveAndDeregister(); |
| * }}</pre> |
| * |
| * |
| * <p>To create a set of {@code n} tasks using a tree of phasers, you |
| * could use code of the following form, assuming a Task class with a |
| * constructor accepting a {@code Phaser} that it registers with upon |
| * construction. After invocation of {@code build(new Task[n], 0, n, |
| * new Phaser())}, these tasks could then be started, for example by |
| * submitting to a pool: |
| * |
| * <pre> {@code |
| * void build(Task[] tasks, int lo, int hi, Phaser ph) { |
| * if (hi - lo > TASKS_PER_PHASER) { |
| * for (int i = lo; i < hi; i += TASKS_PER_PHASER) { |
| * int j = Math.min(i + TASKS_PER_PHASER, hi); |
| * build(tasks, i, j, new Phaser(ph)); |
| * } |
| * } else { |
| * for (int i = lo; i < hi; ++i) |
| * tasks[i] = new Task(ph); |
| * // assumes new Task(ph) performs ph.register() |
| * } |
| * }}</pre> |
| * |
| * The best value of {@code TASKS_PER_PHASER} depends mainly on |
| * expected synchronization rates. A value as low as four may |
| * be appropriate for extremely small per-phase task bodies (thus |
| * high rates), or up to hundreds for extremely large ones. |
| * |
| * <p><b>Implementation notes</b>: This implementation restricts the |
| * maximum number of parties to 65535. Attempts to register additional |
| * parties result in {@code IllegalStateException}. However, you can and |
| * should create tiered phasers to accommodate arbitrarily large sets |
| * of participants. |
| * |
| * @since 1.7 |
| * @author Doug Lea |
| */ |
| public class Phaser { |
| /* |
| * This class implements an extension of X10 "clocks". Thanks to |
| * Vijay Saraswat for the idea, and to Vivek Sarkar for |
| * enhancements to extend functionality. |
| */ |
| |
| /** |
| * Primary state representation, holding four bit-fields: |
| * |
| * unarrived -- the number of parties yet to hit barrier (bits 0-15) |
| * parties -- the number of parties to wait (bits 16-31) |
| * phase -- the generation of the barrier (bits 32-62) |
| * terminated -- set if barrier is terminated (bit 63 / sign) |
| * |
| * Except that a phaser with no registered parties is |
| * distinguished by the otherwise illegal state of having zero |
| * parties and one unarrived parties (encoded as EMPTY below). |
| * |
| * To efficiently maintain atomicity, these values are packed into |
| * a single (atomic) long. Good performance relies on keeping |
| * state decoding and encoding simple, and keeping race windows |
| * short. |
| * |
| * All state updates are performed via CAS except initial |
| * registration of a sub-phaser (i.e., one with a non-null |
| * parent). In this (relatively rare) case, we use built-in |
| * synchronization to lock while first registering with its |
| * parent. |
| * |
| * The phase of a subphaser is allowed to lag that of its |
| * ancestors until it is actually accessed -- see method |
| * reconcileState. |
| */ |
| private volatile long state; |
| |
| private static final int MAX_PARTIES = 0xffff; |
| private static final int MAX_PHASE = Integer.MAX_VALUE; |
| private static final int PARTIES_SHIFT = 16; |
| private static final int PHASE_SHIFT = 32; |
| private static final int UNARRIVED_MASK = 0xffff; // to mask ints |
| private static final long PARTIES_MASK = 0xffff0000L; // to mask longs |
| private static final long COUNTS_MASK = 0xffffffffL; |
| private static final long TERMINATION_BIT = 1L << 63; |
| |
| // some special values |
| private static final int ONE_ARRIVAL = 1; |
| private static final int ONE_PARTY = 1 << PARTIES_SHIFT; |
| private static final int ONE_DEREGISTER = ONE_ARRIVAL|ONE_PARTY; |
| private static final int EMPTY = 1; |
| |
| // The following unpacking methods are usually manually inlined |
| |
| private static int unarrivedOf(long s) { |
| int counts = (int)s; |
| return (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK); |
| } |
| |
| private static int partiesOf(long s) { |
| return (int)s >>> PARTIES_SHIFT; |
| } |
| |
| private static int phaseOf(long s) { |
| return (int)(s >>> PHASE_SHIFT); |
| } |
| |
| private static int arrivedOf(long s) { |
| int counts = (int)s; |
| return (counts == EMPTY) ? 0 : |
| (counts >>> PARTIES_SHIFT) - (counts & UNARRIVED_MASK); |
| } |
| |
| /** |
| * The parent of this phaser, or null if none. |
| */ |
| private final Phaser parent; |
| |
| /** |
| * The root of phaser tree. Equals this if not in a tree. |
| */ |
| private final Phaser root; |
| |
| /** |
| * Heads of Treiber stacks for waiting threads. To eliminate |
| * contention when releasing some threads while adding others, we |
| * use two of them, alternating across even and odd phases. |
| * Subphasers share queues with root to speed up releases. |
| */ |
| private final AtomicReference<QNode> evenQ; |
| private final AtomicReference<QNode> oddQ; |
| |
| private AtomicReference<QNode> queueFor(int phase) { |
| return ((phase & 1) == 0) ? evenQ : oddQ; |
| } |
| |
| /** |
| * Returns message string for bounds exceptions on arrival. |
| */ |
| private String badArrive(long s) { |
| return "Attempted arrival of unregistered party for " + |
| stateToString(s); |
| } |
| |
| /** |
| * Returns message string for bounds exceptions on registration. |
| */ |
| private String badRegister(long s) { |
| return "Attempt to register more than " + |
| MAX_PARTIES + " parties for " + stateToString(s); |
| } |
| |
| /** |
| * Main implementation for methods arrive and arriveAndDeregister. |
| * Manually tuned to speed up and minimize race windows for the |
| * common case of just decrementing unarrived field. |
| * |
| * @param adjust value to subtract from state; |
| * ONE_ARRIVAL for arrive, |
| * ONE_DEREGISTER for arriveAndDeregister |
| */ |
| private int doArrive(int adjust) { |
| final Phaser root = this.root; |
| for (;;) { |
| long s = (root == this) ? state : reconcileState(); |
| int phase = (int)(s >>> PHASE_SHIFT); |
| if (phase < 0) |
| return phase; |
| int counts = (int)s; |
| int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK); |
| if (unarrived <= 0) |
| throw new IllegalStateException(badArrive(s)); |
| if (U.compareAndSwapLong(this, STATE, s, s-=adjust)) { |
| if (unarrived == 1) { |
| long n = s & PARTIES_MASK; // base of next state |
| int nextUnarrived = (int)n >>> PARTIES_SHIFT; |
| if (root == this) { |
| if (onAdvance(phase, nextUnarrived)) |
| n |= TERMINATION_BIT; |
| else if (nextUnarrived == 0) |
| n |= EMPTY; |
| else |
| n |= nextUnarrived; |
| int nextPhase = (phase + 1) & MAX_PHASE; |
| n |= (long)nextPhase << PHASE_SHIFT; |
| U.compareAndSwapLong(this, STATE, s, n); |
| releaseWaiters(phase); |
| } |
| else if (nextUnarrived == 0) { // propagate deregistration |
| phase = parent.doArrive(ONE_DEREGISTER); |
| U.compareAndSwapLong(this, STATE, s, s | EMPTY); |
| } |
| else |
| phase = parent.doArrive(ONE_ARRIVAL); |
| } |
| return phase; |
| } |
| } |
| } |
| |
| /** |
| * Implementation of register, bulkRegister. |
| * |
| * @param registrations number to add to both parties and |
| * unarrived fields. Must be greater than zero. |
| */ |
| private int doRegister(int registrations) { |
| // adjustment to state |
| long adjust = ((long)registrations << PARTIES_SHIFT) | registrations; |
| final Phaser parent = this.parent; |
| int phase; |
| for (;;) { |
| long s = (parent == null) ? state : reconcileState(); |
| int counts = (int)s; |
| int parties = counts >>> PARTIES_SHIFT; |
| int unarrived = counts & UNARRIVED_MASK; |
| if (registrations > MAX_PARTIES - parties) |
| throw new IllegalStateException(badRegister(s)); |
| phase = (int)(s >>> PHASE_SHIFT); |
| if (phase < 0) |
| break; |
| if (counts != EMPTY) { // not 1st registration |
| if (parent == null || reconcileState() == s) { |
| if (unarrived == 0) // wait out advance |
| root.internalAwaitAdvance(phase, null); |
| else if (U.compareAndSwapLong(this, STATE, s, s + adjust)) |
| break; |
| } |
| } |
| else if (parent == null) { // 1st root registration |
| long next = ((long)phase << PHASE_SHIFT) | adjust; |
| if (U.compareAndSwapLong(this, STATE, s, next)) |
| break; |
| } |
| else { |
| synchronized (this) { // 1st sub registration |
| if (state == s) { // recheck under lock |
| phase = parent.doRegister(1); |
| if (phase < 0) |
| break; |
| // finish registration whenever parent registration |
| // succeeded, even when racing with termination, |
| // since these are part of the same "transaction". |
| while (!U.compareAndSwapLong |
| (this, STATE, s, |
| ((long)phase << PHASE_SHIFT) | adjust)) { |
| s = state; |
| phase = (int)(root.state >>> PHASE_SHIFT); |
| // assert (int)s == EMPTY; |
| } |
| break; |
| } |
| } |
| } |
| } |
| return phase; |
| } |
| |
| /** |
| * Resolves lagged phase propagation from root if necessary. |
| * Reconciliation normally occurs when root has advanced but |
| * subphasers have not yet done so, in which case they must finish |
| * their own advance by setting unarrived to parties (or if |
| * parties is zero, resetting to unregistered EMPTY state). |
| * |
| * @return reconciled state |
| */ |
| private long reconcileState() { |
| final Phaser root = this.root; |
| long s = state; |
| if (root != this) { |
| int phase, p; |
| // CAS to root phase with current parties, tripping unarrived |
| while ((phase = (int)(root.state >>> PHASE_SHIFT)) != |
| (int)(s >>> PHASE_SHIFT) && |
| !U.compareAndSwapLong |
| (this, STATE, s, |
| s = (((long)phase << PHASE_SHIFT) | |
| ((phase < 0) ? (s & COUNTS_MASK) : |
| (((p = (int)s >>> PARTIES_SHIFT) == 0) ? EMPTY : |
| ((s & PARTIES_MASK) | p)))))) |
| s = state; |
| } |
| return s; |
| } |
| |
| /** |
| * Creates a new phaser with no initially registered parties, no |
| * parent, and initial phase number 0. Any thread using this |
| * phaser will need to first register for it. |
| */ |
| public Phaser() { |
| this(null, 0); |
| } |
| |
| /** |
| * Creates a new phaser with the given number of registered |
| * unarrived parties, no parent, and initial phase number 0. |
| * |
| * @param parties the number of parties required to advance to the |
| * next phase |
| * @throws IllegalArgumentException if parties less than zero |
| * or greater than the maximum number of parties supported |
| */ |
| public Phaser(int parties) { |
| this(null, parties); |
| } |
| |
| /** |
| * Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}. |
| * |
| * @param parent the parent phaser |
| */ |
| public Phaser(Phaser parent) { |
| this(parent, 0); |
| } |
| |
| /** |
| * Creates a new phaser with the given parent and number of |
| * registered unarrived parties. When the given parent is non-null |
| * and the given number of parties is greater than zero, this |
| * child phaser is registered with its parent. |
| * |
| * @param parent the parent phaser |
| * @param parties the number of parties required to advance to the |
| * next phase |
| * @throws IllegalArgumentException if parties less than zero |
| * or greater than the maximum number of parties supported |
| */ |
| public Phaser(Phaser parent, int parties) { |
| if (parties >>> PARTIES_SHIFT != 0) |
| throw new IllegalArgumentException("Illegal number of parties"); |
| int phase = 0; |
| this.parent = parent; |
| if (parent != null) { |
| final Phaser root = parent.root; |
| this.root = root; |
| this.evenQ = root.evenQ; |
| this.oddQ = root.oddQ; |
| if (parties != 0) |
| phase = parent.doRegister(1); |
| } |
| else { |
| this.root = this; |
| this.evenQ = new AtomicReference<QNode>(); |
| this.oddQ = new AtomicReference<QNode>(); |
| } |
| this.state = (parties == 0) ? (long)EMPTY : |
| ((long)phase << PHASE_SHIFT) | |
| ((long)parties << PARTIES_SHIFT) | |
| ((long)parties); |
| } |
| |
| /** |
| * Adds a new unarrived party to this phaser. If an ongoing |
| * invocation of {@link #onAdvance} is in progress, this method |
| * may await its completion before returning. If this phaser has |
| * a parent, and this phaser previously had no registered parties, |
| * this child phaser is also registered with its parent. If |
| * this phaser is terminated, the attempt to register has |
| * no effect, and a negative value is returned. |
| * |
| * @return the arrival phase number to which this registration |
| * applied. If this value is negative, then this phaser has |
| * terminated, in which case registration has no effect. |
| * @throws IllegalStateException if attempting to register more |
| * than the maximum supported number of parties |
| */ |
| public int register() { |
| return doRegister(1); |
| } |
| |
| /** |
| * Adds the given number of new unarrived parties to this phaser. |
| * If an ongoing invocation of {@link #onAdvance} is in progress, |
| * this method may await its completion before returning. If this |
| * phaser has a parent, and the given number of parties is greater |
| * than zero, and this phaser previously had no registered |
| * parties, this child phaser is also registered with its parent. |
| * If this phaser is terminated, the attempt to register has no |
| * effect, and a negative value is returned. |
| * |
| * @param parties the number of additional parties required to |
| * advance to the next phase |
| * @return the arrival phase number to which this registration |
| * applied. If this value is negative, then this phaser has |
| * terminated, in which case registration has no effect. |
| * @throws IllegalStateException if attempting to register more |
| * than the maximum supported number of parties |
| * @throws IllegalArgumentException if {@code parties < 0} |
| */ |
| public int bulkRegister(int parties) { |
| if (parties < 0) |
| throw new IllegalArgumentException(); |
| if (parties == 0) |
| return getPhase(); |
| return doRegister(parties); |
| } |
| |
| /** |
| * Arrives at this phaser, without waiting for others to arrive. |
| * |
| * <p>It is a usage error for an unregistered party to invoke this |
| * method. However, this error may result in an {@code |
| * IllegalStateException} only upon some subsequent operation on |
| * this phaser, if ever. |
| * |
| * @return the arrival phase number, or a negative value if terminated |
| * @throws IllegalStateException if not terminated and the number |
| * of unarrived parties would become negative |
| */ |
| public int arrive() { |
| return doArrive(ONE_ARRIVAL); |
| } |
| |
| /** |
| * Arrives at this phaser and deregisters from it without waiting |
| * for others to arrive. Deregistration reduces the number of |
| * parties required to advance in future phases. If this phaser |
| * has a parent, and deregistration causes this phaser to have |
| * zero parties, this phaser is also deregistered from its parent. |
| * |
| * <p>It is a usage error for an unregistered party to invoke this |
| * method. However, this error may result in an {@code |
| * IllegalStateException} only upon some subsequent operation on |
| * this phaser, if ever. |
| * |
| * @return the arrival phase number, or a negative value if terminated |
| * @throws IllegalStateException if not terminated and the number |
| * of registered or unarrived parties would become negative |
| */ |
| public int arriveAndDeregister() { |
| return doArrive(ONE_DEREGISTER); |
| } |
| |
| /** |
| * Arrives at this phaser and awaits others. Equivalent in effect |
| * to {@code awaitAdvance(arrive())}. If you need to await with |
| * interruption or timeout, you can arrange this with an analogous |
| * construction using one of the other forms of the {@code |
| * awaitAdvance} method. If instead you need to deregister upon |
| * arrival, use {@code awaitAdvance(arriveAndDeregister())}. |
| * |
| * <p>It is a usage error for an unregistered party to invoke this |
| * method. However, this error may result in an {@code |
| * IllegalStateException} only upon some subsequent operation on |
| * this phaser, if ever. |
| * |
| * @return the arrival phase number, or the (negative) |
| * {@linkplain #getPhase() current phase} if terminated |
| * @throws IllegalStateException if not terminated and the number |
| * of unarrived parties would become negative |
| */ |
| public int arriveAndAwaitAdvance() { |
| // Specialization of doArrive+awaitAdvance eliminating some reads/paths |
| final Phaser root = this.root; |
| for (;;) { |
| long s = (root == this) ? state : reconcileState(); |
| int phase = (int)(s >>> PHASE_SHIFT); |
| if (phase < 0) |
| return phase; |
| int counts = (int)s; |
| int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK); |
| if (unarrived <= 0) |
| throw new IllegalStateException(badArrive(s)); |
| if (U.compareAndSwapLong(this, STATE, s, s -= ONE_ARRIVAL)) { |
| if (unarrived > 1) |
| return root.internalAwaitAdvance(phase, null); |
| if (root != this) |
| return parent.arriveAndAwaitAdvance(); |
| long n = s & PARTIES_MASK; // base of next state |
| int nextUnarrived = (int)n >>> PARTIES_SHIFT; |
| if (onAdvance(phase, nextUnarrived)) |
| n |= TERMINATION_BIT; |
| else if (nextUnarrived == 0) |
| n |= EMPTY; |
| else |
| n |= nextUnarrived; |
| int nextPhase = (phase + 1) & MAX_PHASE; |
| n |= (long)nextPhase << PHASE_SHIFT; |
| if (!U.compareAndSwapLong(this, STATE, s, n)) |
| return (int)(state >>> PHASE_SHIFT); // terminated |
| releaseWaiters(phase); |
| return nextPhase; |
| } |
| } |
| } |
| |
| /** |
| * Awaits the phase of this phaser to advance from the given phase |
| * value, returning immediately if the current phase is not equal |
| * to the given phase value or this phaser is terminated. |
| * |
| * @param phase an arrival phase number, or negative value if |
| * terminated; this argument is normally the value returned by a |
| * previous call to {@code arrive} or {@code arriveAndDeregister}. |
| * @return the next arrival phase number, or the argument if it is |
| * negative, or the (negative) {@linkplain #getPhase() current phase} |
| * if terminated |
| */ |
| public int awaitAdvance(int phase) { |
| final Phaser root = this.root; |
| long s = (root == this) ? state : reconcileState(); |
| int p = (int)(s >>> PHASE_SHIFT); |
| if (phase < 0) |
| return phase; |
| if (p == phase) |
| return root.internalAwaitAdvance(phase, null); |
| return p; |
| } |
| |
| /** |
| * Awaits the phase of this phaser to advance from the given phase |
| * value, throwing {@code InterruptedException} if interrupted |
| * while waiting, or returning immediately if the current phase is |
| * not equal to the given phase value or this phaser is |
| * terminated. |
| * |
| * @param phase an arrival phase number, or negative value if |
| * terminated; this argument is normally the value returned by a |
| * previous call to {@code arrive} or {@code arriveAndDeregister}. |
| * @return the next arrival phase number, or the argument if it is |
| * negative, or the (negative) {@linkplain #getPhase() current phase} |
| * if terminated |
| * @throws InterruptedException if thread interrupted while waiting |
| */ |
| public int awaitAdvanceInterruptibly(int phase) |
| throws InterruptedException { |
| final Phaser root = this.root; |
| long s = (root == this) ? state : reconcileState(); |
| int p = (int)(s >>> PHASE_SHIFT); |
| if (phase < 0) |
| return phase; |
| if (p == phase) { |
| QNode node = new QNode(this, phase, true, false, 0L); |
| p = root.internalAwaitAdvance(phase, node); |
| if (node.wasInterrupted) |
| throw new InterruptedException(); |
| } |
| return p; |
| } |
| |
| /** |
| * Awaits the phase of this phaser to advance from the given phase |
| * value or the given timeout to elapse, throwing {@code |
| * InterruptedException} if interrupted while waiting, or |
| * returning immediately if the current phase is not equal to the |
| * given phase value or this phaser is terminated. |
| * |
| * @param phase an arrival phase number, or negative value if |
| * terminated; this argument is normally the value returned by a |
| * previous call to {@code arrive} or {@code arriveAndDeregister}. |
| * @param timeout how long to wait before giving up, in units of |
| * {@code unit} |
| * @param unit a {@code TimeUnit} determining how to interpret the |
| * {@code timeout} parameter |
| * @return the next arrival phase number, or the argument if it is |
| * negative, or the (negative) {@linkplain #getPhase() current phase} |
| * if terminated |
| * @throws InterruptedException if thread interrupted while waiting |
| * @throws TimeoutException if timed out while waiting |
| */ |
| public int awaitAdvanceInterruptibly(int phase, |
| long timeout, TimeUnit unit) |
| throws InterruptedException, TimeoutException { |
| long nanos = unit.toNanos(timeout); |
| final Phaser root = this.root; |
| long s = (root == this) ? state : reconcileState(); |
| int p = (int)(s >>> PHASE_SHIFT); |
| if (phase < 0) |
| return phase; |
| if (p == phase) { |
| QNode node = new QNode(this, phase, true, true, nanos); |
| p = root.internalAwaitAdvance(phase, node); |
| if (node.wasInterrupted) |
| throw new InterruptedException(); |
| else if (p == phase) |
| throw new TimeoutException(); |
| } |
| return p; |
| } |
| |
| /** |
| * Forces this phaser to enter termination state. Counts of |
| * registered parties are unaffected. If this phaser is a member |
| * of a tiered set of phasers, then all of the phasers in the set |
| * are terminated. If this phaser is already terminated, this |
| * method has no effect. This method may be useful for |
| * coordinating recovery after one or more tasks encounter |
| * unexpected exceptions. |
| */ |
| public void forceTermination() { |
| // Only need to change root state |
| final Phaser root = this.root; |
| long s; |
| while ((s = root.state) >= 0) { |
| if (U.compareAndSwapLong(root, STATE, s, s | TERMINATION_BIT)) { |
| // signal all threads |
| releaseWaiters(0); // Waiters on evenQ |
| releaseWaiters(1); // Waiters on oddQ |
| return; |
| } |
| } |
| } |
| |
| /** |
| * Returns the current phase number. The maximum phase number is |
| * {@code Integer.MAX_VALUE}, after which it restarts at |
| * zero. Upon termination, the phase number is negative, |
| * in which case the prevailing phase prior to termination |
| * may be obtained via {@code getPhase() + Integer.MIN_VALUE}. |
| * |
| * @return the phase number, or a negative value if terminated |
| */ |
| public final int getPhase() { |
| return (int)(root.state >>> PHASE_SHIFT); |
| } |
| |
| /** |
| * Returns the number of parties registered at this phaser. |
| * |
| * @return the number of parties |
| */ |
| public int getRegisteredParties() { |
| return partiesOf(state); |
| } |
| |
| /** |
| * Returns the number of registered parties that have arrived at |
| * the current phase of this phaser. If this phaser has terminated, |
| * the returned value is meaningless and arbitrary. |
| * |
| * @return the number of arrived parties |
| */ |
| public int getArrivedParties() { |
| return arrivedOf(reconcileState()); |
| } |
| |
| /** |
| * Returns the number of registered parties that have not yet |
| * arrived at the current phase of this phaser. If this phaser has |
| * terminated, the returned value is meaningless and arbitrary. |
| * |
| * @return the number of unarrived parties |
| */ |
| public int getUnarrivedParties() { |
| return unarrivedOf(reconcileState()); |
| } |
| |
| /** |
| * Returns the parent of this phaser, or {@code null} if none. |
| * |
| * @return the parent of this phaser, or {@code null} if none |
| */ |
| public Phaser getParent() { |
| return parent; |
| } |
| |
| /** |
| * Returns the root ancestor of this phaser, which is the same as |
| * this phaser if it has no parent. |
| * |
| * @return the root ancestor of this phaser |
| */ |
| public Phaser getRoot() { |
| return root; |
| } |
| |
| /** |
| * Returns {@code true} if this phaser has been terminated. |
| * |
| * @return {@code true} if this phaser has been terminated |
| */ |
| public boolean isTerminated() { |
| return root.state < 0L; |
| } |
| |
| /** |
| * Overridable method to perform an action upon impending phase |
| * advance, and to control termination. This method is invoked |
| * upon arrival of the party advancing this phaser (when all other |
| * waiting parties are dormant). If this method returns {@code |
| * true}, this phaser will be set to a final termination state |
| * upon advance, and subsequent calls to {@link #isTerminated} |
| * will return true. Any (unchecked) Exception or Error thrown by |
| * an invocation of this method is propagated to the party |
| * attempting to advance this phaser, in which case no advance |
| * occurs. |
| * |
| * <p>The arguments to this method provide the state of the phaser |
| * prevailing for the current transition. The effects of invoking |
| * arrival, registration, and waiting methods on this phaser from |
| * within {@code onAdvance} are unspecified and should not be |
| * relied on. |
| * |
| * <p>If this phaser is a member of a tiered set of phasers, then |
| * {@code onAdvance} is invoked only for its root phaser on each |
| * advance. |
| * |
| * <p>To support the most common use cases, the default |
| * implementation of this method returns {@code true} when the |
| * number of registered parties has become zero as the result of a |
| * party invoking {@code arriveAndDeregister}. You can disable |
| * this behavior, thus enabling continuation upon future |
| * registrations, by overriding this method to always return |
| * {@code false}: |
| * |
| * <pre> {@code |
| * Phaser phaser = new Phaser() { |
| * protected boolean onAdvance(int phase, int parties) { return false; } |
| * }}</pre> |
| * |
| * @param phase the current phase number on entry to this method, |
| * before this phaser is advanced |
| * @param registeredParties the current number of registered parties |
| * @return {@code true} if this phaser should terminate |
| */ |
| protected boolean onAdvance(int phase, int registeredParties) { |
| return registeredParties == 0; |
| } |
| |
| /** |
| * Returns a string identifying this phaser, as well as its |
| * state. The state, in brackets, includes the String {@code |
| * "phase = "} followed by the phase number, {@code "parties = "} |
| * followed by the number of registered parties, and {@code |
| * "arrived = "} followed by the number of arrived parties. |
| * |
| * @return a string identifying this phaser, as well as its state |
| */ |
| public String toString() { |
| return stateToString(reconcileState()); |
| } |
| |
| /** |
| * Implementation of toString and string-based error messages. |
| */ |
| private String stateToString(long s) { |
| return super.toString() + |
| "[phase = " + phaseOf(s) + |
| " parties = " + partiesOf(s) + |
| " arrived = " + arrivedOf(s) + "]"; |
| } |
| |
| // Waiting mechanics |
| |
| /** |
| * Removes and signals threads from queue for phase. |
| */ |
| private void releaseWaiters(int phase) { |
| QNode q; // first element of queue |
| Thread t; // its thread |
| AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; |
| while ((q = head.get()) != null && |
| q.phase != (int)(root.state >>> PHASE_SHIFT)) { |
| if (head.compareAndSet(q, q.next) && |
| (t = q.thread) != null) { |
| q.thread = null; |
| LockSupport.unpark(t); |
| } |
| } |
| } |
| |
| /** |
| * Variant of releaseWaiters that additionally tries to remove any |
| * nodes no longer waiting for advance due to timeout or |
| * interrupt. Currently, nodes are removed only if they are at |
| * head of queue, which suffices to reduce memory footprint in |
| * most usages. |
| * |
| * @return current phase on exit |
| */ |
| private int abortWait(int phase) { |
| AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; |
| for (;;) { |
| Thread t; |
| QNode q = head.get(); |
| int p = (int)(root.state >>> PHASE_SHIFT); |
| if (q == null || ((t = q.thread) != null && q.phase == p)) |
| return p; |
| if (head.compareAndSet(q, q.next) && t != null) { |
| q.thread = null; |
| LockSupport.unpark(t); |
| } |
| } |
| } |
| |
| /** The number of CPUs, for spin control */ |
| private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
| |
| /** |
| * The number of times to spin before blocking while waiting for |
| * advance, per arrival while waiting. On multiprocessors, fully |
| * blocking and waking up a large number of threads all at once is |
| * usually a very slow process, so we use rechargeable spins to |
| * avoid it when threads regularly arrive: When a thread in |
| * internalAwaitAdvance notices another arrival before blocking, |
| * and there appear to be enough CPUs available, it spins |
| * SPINS_PER_ARRIVAL more times before blocking. The value trades |
| * off good-citizenship vs big unnecessary slowdowns. |
| */ |
| static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8; |
| |
| /** |
| * Possibly blocks and waits for phase to advance unless aborted. |
| * Call only on root phaser. |
| * |
| * @param phase current phase |
| * @param node if non-null, the wait node to track interrupt and timeout; |
| * if null, denotes noninterruptible wait |
| * @return current phase |
| */ |
| private int internalAwaitAdvance(int phase, QNode node) { |
| // assert root == this; |
| releaseWaiters(phase-1); // ensure old queue clean |
| boolean queued = false; // true when node is enqueued |
| int lastUnarrived = 0; // to increase spins upon change |
| int spins = SPINS_PER_ARRIVAL; |
| long s; |
| int p; |
| while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) { |
| if (node == null) { // spinning in noninterruptible mode |
| int unarrived = (int)s & UNARRIVED_MASK; |
| if (unarrived != lastUnarrived && |
| (lastUnarrived = unarrived) < NCPU) |
| spins += SPINS_PER_ARRIVAL; |
| boolean interrupted = Thread.interrupted(); |
| if (interrupted || --spins < 0) { // need node to record intr |
| node = new QNode(this, phase, false, false, 0L); |
| node.wasInterrupted = interrupted; |
| } |
| } |
| else if (node.isReleasable()) // done or aborted |
| break; |
| else if (!queued) { // push onto queue |
| AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ; |
| QNode q = node.next = head.get(); |
| if ((q == null || q.phase == phase) && |
| (int)(state >>> PHASE_SHIFT) == phase) // avoid stale enq |
| queued = head.compareAndSet(q, node); |
| } |
| else { |
| try { |
| ForkJoinPool.managedBlock(node); |
| } catch (InterruptedException cantHappen) { |
| node.wasInterrupted = true; |
| } |
| } |
| } |
| |
| if (node != null) { |
| if (node.thread != null) |
| node.thread = null; // avoid need for unpark() |
| if (node.wasInterrupted && !node.interruptible) |
| Thread.currentThread().interrupt(); |
| if (p == phase && (p = (int)(state >>> PHASE_SHIFT)) == phase) |
| return abortWait(phase); // possibly clean up on abort |
| } |
| releaseWaiters(phase); |
| return p; |
| } |
| |
| /** |
| * Wait nodes for Treiber stack representing wait queue. |
| */ |
| static final class QNode implements ForkJoinPool.ManagedBlocker { |
| final Phaser phaser; |
| final int phase; |
| final boolean interruptible; |
| final boolean timed; |
| boolean wasInterrupted; |
| long nanos; |
| final long deadline; |
| volatile Thread thread; // nulled to cancel wait |
| QNode next; |
| |
| QNode(Phaser phaser, int phase, boolean interruptible, |
| boolean timed, long nanos) { |
| this.phaser = phaser; |
| this.phase = phase; |
| this.interruptible = interruptible; |
| this.nanos = nanos; |
| this.timed = timed; |
| this.deadline = timed ? System.nanoTime() + nanos : 0L; |
| thread = Thread.currentThread(); |
| } |
| |
| public boolean isReleasable() { |
| if (thread == null) |
| return true; |
| if (phaser.getPhase() != phase) { |
| thread = null; |
| return true; |
| } |
| if (Thread.interrupted()) |
| wasInterrupted = true; |
| if (wasInterrupted && interruptible) { |
| thread = null; |
| return true; |
| } |
| if (timed && |
| (nanos <= 0L || (nanos = deadline - System.nanoTime()) <= 0L)) { |
| thread = null; |
| return true; |
| } |
| return false; |
| } |
| |
| public boolean block() { |
| while (!isReleasable()) { |
| if (timed) |
| LockSupport.parkNanos(this, nanos); |
| else |
| LockSupport.park(this); |
| } |
| return true; |
| } |
| } |
| |
| // Unsafe mechanics |
| |
| private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe(); |
| private static final long STATE; |
| static { |
| try { |
| STATE = U.objectFieldOffset |
| (Phaser.class.getDeclaredField("state")); |
| } catch (ReflectiveOperationException e) { |
| throw new Error(e); |
| } |
| |
| // Reduce the risk of rare disastrous classloading in first call to |
| // LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773 |
| Class<?> ensureLoaded = LockSupport.class; |
| } |
| } |
