--- jsr166/src/jsr166y/Phaser.java 2009/07/23 23:07:57 1.18 +++ jsr166/src/jsr166y/Phaser.java 2010/11/28 15:49:49 1.60 @@ -6,158 +6,199 @@ package jsr166y; -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; -import sun.misc.Unsafe; -import java.lang.reflect.*; /** - * A reusable synchronization barrier, similar in functionality to a + * 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 usages: * - *
A 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 {@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: * *
{@code - * void runTasks(List* *list) { + * void runTasks(List tasks) { * final Phaser phaser = new Phaser(1); // "1" to register self - * for (Runnable r : list) { + * // create and start threads + * for (Runnable task : tasks) { * phaser.register(); * new Thread() { * public void run() { * phaser.arriveAndAwaitAdvance(); // await all creation - * r.run(); - * phaser.arriveAndDeregister(); // signal completion + * task.run(); * } * }.start(); * } * - * doSomethingOnBehalfOfWorkers(); - * phaser.arrive(); // allow threads to start - * int p = phaser.arriveAndDeregister(); // deregister self ... - * p = phaser.awaitAdvance(p); // ... and await arrival - * otherActions(); // do other things while tasks execute - * phaser.awaitAdvance(p); // await final completion + * // 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* - *list, final int iterations) { + * void startTasks(List tasks, final int iterations) { * final Phaser phaser = new Phaser() { - * public boolean onAdvance(int phase, int registeredParties) { + * protected boolean onAdvance(int phase, int registeredParties) { * return phase >= iterations || registeredParties == 0; * } * }; * phaser.register(); - * for (Runnable r : list) { + * for (final Runnable task : tasks) { * phaser.register(); * new Thread() { * public void run() { * do { - * r.run(); + * task.run(); * phaser.arriveAndAwaitAdvance(); - * } while(!phaser.isTerminated(); + * } while (!phaser.isTerminated()); * } * }.start(); * } * phaser.arriveAndDeregister(); // deregister self, don't wait * }}
To create a set of tasks using a tree of Phasers, + * If the main task must later await termination, it + * may re-register and then execute a similar loop: + *
{@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 for upon construction: + * it registers with upon construction: + * *
{@code - * void build(Task[] actions, int lo, int hi, Phaser b) { - * int step = (hi - lo) / TASKS_PER_PHASER; - * if (step > 1) { - * int i = lo; - * while (i < hi) { - * int r = Math.min(i + step, hi); - * build(actions, i, r, new Phaser(b)); - * i = r; + * 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(b); - * // assumes new Task(b) performs b.register() + * actions[i] = new Task(ph); + * // assumes new Task(ph) performs ph.register() * } * } * // .. initially called, for n tasks via @@ -168,12 +209,10 @@ import java.lang.reflect.*; * be appropriate for extremely small per-barrier task bodies (thus * high rates), or up to hundreds for extremely large ones. * - *- * *
Implementation notes: This implementation restricts the
* maximum number of parties to 65535. Attempts to register additional
- * parties result in IllegalStateExceptions. However, you can and
- * should create tiered phasers to accommodate arbitrarily large sets
+ * parties result in {@code IllegalStateException}. However, you can and
+ * should create tiered Phasers to accommodate arbitrarily large sets
* of participants.
*
* @since 1.7
@@ -190,111 +229,199 @@ public class Phaser {
* 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 (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.
- *
- * Note: there are some cheats in arrive() that rely on unarrived
- * count being lowest 16 bits.
*/
private volatile long state;
- private static final int ushortBits = 16;
- private static final int ushortMask = 0xffff;
- private static final int phaseMask = 0x7fffffff;
+ 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;
+
+ // The following unpacking methods are usually manually inlined
private static int unarrivedOf(long s) {
- return (int) (s & ushortMask);
+ return (int)s & UNARRIVED_MASK;
}
private static int partiesOf(long s) {
- return ((int) s) >>> 16;
+ return (int)s >>> PARTIES_SHIFT;
}
private static int phaseOf(long s) {
- return (int) (s >>> 32);
+ return (int) (s >>> PHASE_SHIFT);
}
private static int arrivedOf(long s) {
return partiesOf(s) - unarrivedOf(s);
}
- private static long stateFor(int phase, int parties, int unarrived) {
- return ((((long) phase) << 32) | (((long) parties) << 16) |
- (long) unarrived);
- }
-
- private static long trippedStateFor(int phase, int parties) {
- long lp = (long) parties;
- return (((long) phase) << 32) | (lp << 16) | lp;
- }
-
- /**
- * Returns message string for bad bounds exceptions.
- */
- private static String badBounds(int parties, int unarrived) {
- return ("Attempt to set " + unarrived +
- " unarrived of " + parties + " parties");
- }
-
/**
* 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. Used to
+ * The root of phaser tree. Equals this if not in a tree. Used to
* support faster state push-down.
*/
private final Phaser root;
- // Wait queues
-
/**
* Heads of Treiber stacks for waiting threads. To eliminate
- * contention while releasing some threads while adding others, we
+ * 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 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() {
- int phase;
- for (;;) {
- long s = state;
- phase = phaseOf(s);
- if (phase < 0)
- break;
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s) - 1;
- if (unarrived > 0) { // Not the last arrival
- if (casState(s, s - 1)) // s-1 adds one arrival
- break;
- }
- else if (unarrived == 0) { // the last arrival
- Phaser par = parent;
- if (par == null) { // directly trip
- if (casState
- (s,
- trippedStateFor(onAdvance(phase, parties) ? -1 :
- ((phase + 1) & phaseMask), parties))) {
- releaseWaiters(phase);
- break;
- }
- }
- else { // cascade to parent
- if (casState(s, s - 1)) { // zeroes unarrived
- par.arrive();
- reconcileState();
- break;
- }
- }
- }
- else if (phase != phaseOf(root.state)) // or if unreconciled
- reconcileState();
- else
- throw new IllegalStateException(badBounds(parties, unarrived));
- }
- return phase;
+ return doArrive(ONE_ARRIVAL);
}
/**
- * Arrives at the barrier, and deregisters from it, without
- * waiting for others. Deregistration reduces 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.
+ * 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.
*
- * @return the current barrier phase number upon entry to
- * this method, or a negative value if terminated
+ * 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() {
- // similar code to arrive, but too different to merge
- Phaser par = parent;
- int phase;
- for (;;) {
- long s = state;
- phase = phaseOf(s);
- if (phase < 0)
- break;
- int parties = partiesOf(s) - 1;
- int unarrived = unarrivedOf(s) - 1;
- if (parties >= 0) {
- if (unarrived > 0 || (unarrived == 0 && par != null)) {
- if (casState
- (s,
- stateFor(phase, parties, unarrived))) {
- if (unarrived == 0) {
- par.arriveAndDeregister();
- reconcileState();
- }
- break;
- }
- continue;
- }
- if (unarrived == 0) {
- if (casState
- (s,
- trippedStateFor(onAdvance(phase, parties) ? -1 :
- ((phase + 1) & phaseMask), parties))) {
- releaseWaiters(phase);
- break;
- }
- continue;
- }
- if (par != null && phase != phaseOf(root.state)) {
- reconcileState();
- continue;
- }
- }
- throw new IllegalStateException(badBounds(parties, unarrived));
- }
- return phase;
+ return doArrive(ONE_ARRIVAL|ONE_PARTY);
}
/**
* Arrives at the barrier and awaits others. Equivalent in effect
- * to {@code awaitAdvance(arrive())}. If you instead need to
- * await with interruption of timeout, and/or deregister upon
- * arrival, you can arrange them using analogous constructions.
+ * 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 phase on entry to this method
+ * @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
*/
@@ -534,92 +591,116 @@ public class Phaser {
}
/**
- * Awaits the phase of the barrier to advance from the given
- * value, or returns immediately if argument is negative or 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, 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;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
- return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvance(phase);
- // Fall here even if parent waited, to reconcile and help release
- return untimedWait(phase);
+ 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 argument is negative or this
- * barrier is terminated, or throws InterruptedException if
- * interrupted while waiting.
+ * 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 the phase on entry to this method
- * @return the phase on exit from this method
+ * @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 {
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
- return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase);
- return interruptibleWait(phase);
+ 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
- * argument is negative or 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)
throws InterruptedException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
- return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase, timeout, unit);
- return timedWait(phase, unit.toNanos(timeout));
+ 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. If this phaser
- * has a parent, it too is terminated. This method may be useful
- * for coordinating recovery after one or more tasks encounter
- * unexpected exceptions.
+ * 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() {
- for (;;) {
- long s = getReconciledState();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s);
- if (phase < 0 ||
- casState(s, stateFor(-1, parties, unarrived))) {
- releaseWaiters(0);
+ // 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);
- if (parent != null)
- parent.forceTermination();
return;
}
}
@@ -633,17 +714,7 @@ public class Phaser {
* @return the phase number, or a negative value if terminated
*/
public final int getPhase() {
- return phaseOf(getReconciledState());
- }
-
- /**
- * Returns {@code true} if the current phase number equals the given phase.
- *
- * @param phase the phase
- * @return {@code true} if the current phase number equals the given phase
- */
- public final boolean hasPhase(int phase) {
- return phaseOf(getReconciledState()) == phase;
+ return (int)(root.state >>> PHASE_SHIFT);
}
/**
@@ -656,13 +727,17 @@ public class Phaser {
}
/**
- * 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);
+ long s = state;
+ int u = unarrivedOf(s); // only reconcile if possibly needed
+ return (u != 0 || parent == null) ?
+ partiesOf(s) - u :
+ arrivedOf(reconcileState());
}
/**
@@ -672,23 +747,24 @@ public class Phaser {
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(state);
+ int u = unarrivedOf(state);
+ return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
}
/**
- * Returns the parent of this phaser, or null if none.
+ * Returns the parent of this Phaser, or {@code null} if none.
*
- * @return the parent of this phaser, or 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.
+ * 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
+ * @return the root ancestor of this Phaser
*/
public Phaser getRoot() {
return root;
@@ -700,33 +776,43 @@ public class Phaser {
* @return {@code true} if this barrier has been terminated
*/
public boolean isTerminated() {
- return getPhase() < 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 {@code 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.
- *
- * You may override this method to perform an action with side
- * effects visible to participating tasks, but it is in general
- * only sensible to do so in designs where all parties register
- * before any arrive, and all {@code awaitAdvance} at each phase.
- * Otherwise, you cannot ensure lack of interference. In
- * particular, this method may be invoked more than once per
- * transition if other parties successfully register while the
- * invocation of this method is in progress, thus postponing the
- * transition until those parties also arrive, re-triggering this
- * method.
+ * 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
@@ -737,7 +823,7 @@ public class Phaser {
}
/**
- * Returns a string identifying this phaser, 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 = "}
* followed by the number of registered parties, and {@code
@@ -746,14 +832,117 @@ public class Phaser {
* @return a string identifying this barrier, as well as its state
*/
public String toString() {
- long s = getReconciledState();
+ 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) + "]";
}
- // methods for waiting
+ // Waiting mechanics
+
+ /**
+ * Removes and signals threads from queue for phase.
+ */
+ private void releaseWaiters(int phase) {
+ AtomicReference