--- jsr166/src/jsr166y/Phaser.java 2008/07/25 18:10:41 1.2 +++ jsr166/src/jsr166y/Phaser.java 2010/11/28 15:49:49 1.60 @@ -5,691 +5,1058 @@ */ package jsr166y; -import jsr166y.forkjoin.*; -import java.util.concurrent.*; -import java.util.concurrent.atomic.*; + +import java.util.concurrent.TimeUnit; +import java.util.concurrent.TimeoutException; +import java.util.concurrent.atomic.AtomicReference; import java.util.concurrent.locks.LockSupport; /** - * A reusable synchronization barrier, similar in functionality to a - * {@link java.util.concurrent.CyclicBarrier}, but supporting more - * flexible usage. + * 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. * - *
Registration. Unlike the case for other barriers, the + * number of parties registered 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.) * - *
Synchronization. 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 {@code Phaser} has an associated phase number. The + * phase number starts at zero, and advances when all parties arrive + * at the barrier, wrapping around to zero after reaching {@code + * Integer.MAX_VALUE}. The use of phase numbers enables independent + * control of actions upon arrival at a barrier and upon awaiting + * others, via two kinds of methods that may be invoked by any + * registered party: * *
Termination. A {@code Phaser} may enter a + * termination state in which all synchronization methods + * immediately return without updating Phaser state or waiting for + * advance, and indicating (via a negative phase value) that execution + * is complete. 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. * - *
Tiering. Phasers may be tiered (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. * - *
Monitoring. 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. * - *
Sample usage: + *
Sample usages: * - *
[todo: non-FJ example] + *
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: * - *
A Phaser may be used to support a style of programming in - * which a task waits for others to complete, without otherwise - * needing to keep track of which tasks it is waiting for. This is - * similar to the "sync" construct in Cilk and "clocks" in X10. - * Special constructions based on such barriers are available using - * the LinkedAsyncAction and CyclicAction classes, - * but they can be useful in other contexts as well. For a simple - * (but not very useful) example, here is a variant of Fibonacci: - * - *
- * class BarrierFibonacci extends RecursiveAction { - * int argument, result; - * final Phaser parentBarrier; - * BarrierFibonacci(int n, Phaser parentBarrier) { - * this.argument = n; - * this.parentBarrier = parentBarrier; - * parentBarrier.register(); + *+ * + * The best value of {@code TASKS_PER_PHASER} depends mainly on + * expected barrier synchronization rates. A value as low as four may + * be appropriate for extremely small per-barrier task bodies (thus + * high rates), or up to hundreds for extremely large ones. * *{@code + * void runTasks(List+ * + *tasks) { + * final Phaser phaser = new Phaser(1); // "1" to register self + * // create and start threads + * for (Runnable task : tasks) { + * phaser.register(); + * new Thread() { + * public void run() { + * phaser.arriveAndAwaitAdvance(); // await all creation + * task.run(); + * } + * }.start(); * } - * protected void compute() { - * int n = argument; - * if (n <= 1) - * result = n; - * else { - * Phaser childBarrier = new Phaser(1); - * BarrierFibonacci f1 = new BarrierFibonacci(n - 1, childBarrier); - * BarrierFibonacci f2 = new BarrierFibonacci(n - 2, childBarrier); - * f1.fork(); - * f2.fork(); - * childBarrier.arriveAndAwait(); - * result = f1.result + f2.result; + * + * // allow threads to start and deregister self + * phaser.arriveAndDeregister(); + * }} One way to cause a set of threads to repeatedly perform actions + * for a given number of iterations is to override {@code onAdvance}: + * + *
{@code + * void startTasks(List+ * + * If the main task must later await termination, it + * may re-register and then execute a similar loop: + *tasks, final int iterations) { + * final Phaser phaser = new Phaser() { + * protected boolean onAdvance(int phase, int registeredParties) { + * return phase >= iterations || registeredParties == 0; * } - * parentBarrier.arriveAndDeregister(); + * }; + * 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 + * }} {@code + * // ... + * phaser.register(); + * while (!phaser.isTerminated()) + * phaser.arriveAndAwaitAdvance();}+ * + *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: + * + *
{@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(); + * }}+ * + * + *To create a set of tasks using a tree of Phasers, + * you could use code of the following form, assuming a + * Task class with a constructor accepting a Phaser that + * it registers with upon construction: + * + *
{@code + * void build(Task[] actions, 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(actions, i, j, new Phaser(ph)); + * } + * } else { + * for (int i = lo; i < hi; ++i) + * actions[i] = new Task(ph); + * // assumes new Task(ph) performs ph.register() * } * } - *+ * // .. initially called, for n tasks via + * build(new Task[n], 0, n, new Phaser());}
Implementation notes: This implementation restricts the
- * maximum number of parties to 65535. Attempts to register
- * additional parties result in IllegalStateExceptions.
+ * 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 of applying it to ForkJoinTasks,
- * and to Vivek Sarkar for enhancements to extend functionality.
+ * Vijay Saraswat for the idea, and to Vivek Sarkar for
+ * enhancements to extend functionality.
*/
/**
* Barrier state representation. Conceptually, a barrier contains
* four values:
- *
- * * parties -- the number of parties to wait (16 bits)
- * * unarrived -- the number of parties yet to hit barrier (16 bits)
- * * phase -- the generation of the barrier (31 bits)
- * * terminated -- set if barrier is terminated (1 bit)
+ *
+ * * 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)
*
* However, to efficiently maintain atomicity, these values are
- * packed into a single AtomicLong. Termination uses the sign bit
- * of 32 bit representation of phase, so phase is set to -1 on
- * termination.
- */
- private final AtomicLong state;
+ * packed into a single (atomic) long. Termination uses the sign
+ * bit of 32 bit representation of phase, so phase is set to -1 on
+ * termination. Good performance relies on keeping state decoding
+ * and encoding simple, and keeping race windows short.
+ */
+ private volatile long state;
+
+ private static final int MAX_PARTIES = 0xffff;
+ private static final int MAX_PHASE = 0x7fffffff;
+ 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 ONE_ARRIVAL = 1L;
+ private static final long ONE_PARTY = 1L << PARTIES_SHIFT;
+ private static final long TERMINATION_BIT = 1L << 63;
- /**
- * Head of Treiber stack for waiting nonFJ threads.
- */
- private final AtomicReference 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 the barrier and deregisters from it without waiting
+ * for others to arrive. Deregistration reduces the number of
+ * parties required to trip the barrier 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.
+ *
+ * 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_ARRIVAL|ONE_PARTY);
+ }
+
+ /**
+ * Arrives at the barrier 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())}.
+ *
+ * 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 number if terminated
+ * @throws IllegalStateException if not terminated and the number
+ * of unarrived parties would become negative
+ */
+ public int arriveAndAwaitAdvance() {
+ return awaitAdvance(arrive());
+ }
+
+ /**
+ * Awaits the phase of the barrier to advance from the given phase
+ * value, returning immediately if the current phase of the
+ * barrier is not equal to the given phase value or this barrier
+ * 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 its variants
+ * @return the next arrival phase number, or a negative value
+ * if terminated or argument is negative
*/
public int awaitAdvance(int phase) {
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- Thread current = Thread.currentThread();
- if (current instanceof ForkJoinWorkerThread)
- return helpingWait(phase);
- if (untimedWait(current, phase, false))
- current.interrupt();
- return phaseOf(state.get());
+ if (p == phase &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase)
+ return r.internalAwaitAdvance(phase, null);
+ return p;
}
/**
- * Awaits the phase of the barrier to advance from the given
- * value, or returns immediately if this barrier is terminated, or
- * throws InterruptedException if interrupted while waiting.
- * @param phase the phase on entry to this method
- * @return the phase on exit from this method
+ * Awaits the phase of the barrier to advance from the given phase
+ * value, throwing {@code InterruptedException} if interrupted
+ * while waiting, or returning immediately if the current phase of
+ * the barrier is not equal to the given phase value or this
+ * barrier 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 its variants
+ * @return the next arrival phase number, or a negative value
+ * if terminated or argument is negative
* @throws InterruptedException if thread interrupted while waiting
*/
- public int awaitAdvanceInterruptibly(int phase) throws InterruptedException {
+ public int awaitAdvanceInterruptibly(int phase)
+ throws InterruptedException {
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- Thread current = Thread.currentThread();
- if (current instanceof ForkJoinWorkerThread)
- return helpingWait(phase);
- else if (Thread.interrupted() || untimedWait(current, phase, true))
- throw new InterruptedException();
- else
- return phaseOf(state.get());
+ if (p == phase &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = r.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ }
+ return p;
}
/**
- * Awaits the phase of the barrier to advance from the given value
- * or the given timeout elapses, or returns immediately if this
- * barrier is terminated.
- * @param phase the phase on entry to this method
- * @return the phase on exit from this method
+ * Awaits the phase of the barrier 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 of the barrier is
+ * not equal to the given phase value or this barrier 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 its variants
+ * @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 a negative value
+ * if terminated or argument is negative
* @throws InterruptedException if thread interrupted while waiting
* @throws TimeoutException if timed out while waiting
*/
- public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
+ public int awaitAdvanceInterruptibly(int phase,
+ long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long nanos = unit.toNanos(timeout);
- Thread current = Thread.currentThread();
- if (current instanceof ForkJoinWorkerThread)
- return timedHelpingWait(phase, nanos);
- timedWait(current, phase, nanos);
- return phaseOf(state.get());
+ if (p == phase &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = r.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else if (p == phase)
+ throw new TimeoutException();
+ }
+ return p;
}
/**
- * Forces this barrier to enter termination state. Counts of
- * arrived and registered parties are unaffected. This method may
- * be useful for coordinating recovery after one or more tasks
+ * Forces this barrier to enter termination state. Counts of
+ * arrived and 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() {
- final AtomicLong state = this.state;
- for (;;) {
- long s = state.get();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s);
- if (phase < 0 ||
- state.compareAndSet(s, stateFor(-1, parties, unarrived))) {
- if (head.get() != null)
- releaseWaiters(-1);
+ // Only need to change root state
+ final Phaser root = this.root;
+ long s;
+ while ((s = root.state) >= 0) {
+ if (UNSAFE.compareAndSwapLong(root, stateOffset,
+ s, s | TERMINATION_BIT)) {
+ releaseWaiters(0); // signal all threads
+ releaseWaiters(1);
return;
}
}
}
/**
- * Resets the barrier with the given numbers of registered unarrived
- * parties and phase number 0. This method allows repeated reuse
- * of this barrier, but only if it is somehow known not to be in
- * use for other purposes.
- * @param parties the number of parties required to trip barrier.
- * @throws IllegalArgumentException if parties less than zero
- * or greater than the maximum number of parties supported.
- */
- public void reset(int parties) {
- if (parties < 0 || parties > ushortMask)
- throw new IllegalArgumentException("Illegal number of parties");
- state.set(stateFor(0, parties, parties));
- if (head.get() != null)
- releaseWaiters(0);
- }
-
- /**
* Returns the current phase number. The maximum phase number is
- * Integer.MAX_VALUE, after which it restarts at
+ * {@code Integer.MAX_VALUE}, after which it restarts at
* zero. Upon termination, the phase number is negative.
+ *
* @return the phase number, or a negative value if terminated
*/
- public int getPhase() {
- return phaseOf(state.get());
+ public final int getPhase() {
+ return (int)(root.state >>> PHASE_SHIFT);
}
/**
* Returns the number of parties registered at this barrier.
+ *
* @return the number of parties
*/
public int getRegisteredParties() {
- return partiesOf(state.get());
+ return partiesOf(state);
}
/**
- * Returns the number of parties that have arrived at the current
- * phase of this barrier.
+ * Returns the number of registered parties that have arrived at
+ * the current phase of this barrier.
+ *
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(state.get());
+ long s = state;
+ int u = unarrivedOf(s); // only reconcile if possibly needed
+ return (u != 0 || parent == null) ?
+ partiesOf(s) - u :
+ arrivedOf(reconcileState());
}
/**
* Returns the number of registered parties that have not yet
* arrived at the current phase of this barrier.
+ *
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(state.get());
+ int u = unarrivedOf(state);
+ return (u != 0 || parent == null) ? u : 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 true if this barrier has been terminated.
- * @return true if this barrier has been terminated
+ * Returns {@code true} if this barrier has been terminated.
+ *
+ * @return {@code true} if this barrier has been terminated
*/
public boolean isTerminated() {
- return phaseOf(state.get()) < 0;
+ return root.state < 0L;
}
/**
- * Overridable method to perform an action upon phase advance, and
- * to control termination. This method is invoked whenever the
- * barrier is tripped (and thus all other waiting parties are
- * dormant). If it returns true, then, rather than advance the
- * phase number, this barrier will be set to a final termination
- * state, and subsequent calls to isTerminated will
- * return true.
- *
- * The default version returns true when the number of
- * registered parties is zero. Normally, overrides that arrange
- * termination for other reasons should also preserve this
- * property.
+ * Overridable method to perform an action upon impending phase
+ * advance, and to control termination. This method is invoked
+ * upon arrival of the party tripping the barrier (when all other
+ * waiting parties are dormant). If this method returns {@code
+ * true}, then, rather than advance the phase number, this barrier
+ * will be set to a final termination state, 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 trip the barrier, in
+ * which case no advance occurs.
+ *
+ * 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.
+ *
+ * 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.
+ *
+ * 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}:
+ *
+ * {@code
+ * Phaser phaser = new Phaser() {
+ * protected boolean onAdvance(int phase, int parties) { return false; }
+ * }}
*
* @param phase the phase number on entering the barrier
- * @param registeredParties the current number of registered
- * parties.
- * @return true if this barrier should terminate
+ * @param registeredParties the current number of registered parties
+ * @return {@code true} if this barrier should terminate
*/
protected boolean onAdvance(int phase, int registeredParties) {
return registeredParties <= 0;
}
/**
- * Returns a string identifying this barrier, as well as its
+ * 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 ="}
+ * "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
+ * "arrived = "} followed by the number of arrived parties.
*
* @return a string identifying this barrier, as well as its state
*/
public String toString() {
- long s = state.get();
- return super.toString() + "[phase = " + phaseOf(s) + " parties = " + partiesOf(s) + " arrived = " + arrivedOf(s) + "]";
+ return stateToString(reconcileState());
}
- // methods for tripping and waiting
-
/**
- * Advance the current phase (or terminate)
+ * Implementation of toString and string-based error messages
*/
- private void trip(int phase, int parties) {
- int next = onAdvance(phase, parties)? -1 : ((phase + 1) & phaseMask);
- state.set(stateFor(next, parties, parties));
- if (head.get() != null)
- releaseWaiters(next);
+ private String stateToString(long s) {
+ return super.toString() +
+ "[phase = " + phaseOf(s) +
+ " parties = " + partiesOf(s) +
+ " arrived = " + arrivedOf(s) + "]";
}
- private int helpingWait(int phase) {
- final AtomicLong state = this.state;
+ // Waiting mechanics
+
+ /**
+ * Removes and signals threads from queue for phase.
+ */
+ private void releaseWaiters(int phase) {
+ AtomicReference