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 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: * *
Termination. A 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 {@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: + * 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
* // create and start threads
- * for (Runnable r : list) {
+ * for (Runnable task : tasks) {
* phaser.register();
* new Thread() {
* public void run() {
* phaser.arriveAndAwaitAdvance(); // await all creation
- * r.run();
+ * task.run();
* }
* }.start();
* }
@@ -116,60 +137,81 @@ import java.util.concurrent.locks.LockSu
* 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
* }}
*
+ * 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:
+ * Task class with a constructor accepting a {@code Phaser} that
+ * 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
* build(new Task[n], 0, n, new Phaser());}
*
* 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
+ * 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.
*
- *
- *
* Implementation notes: This implementation restricts the
* maximum number of parties to 65535. Attempts to register additional
- * parties result in IllegalStateExceptions. However, you can and
+ * parties result in {@code IllegalStateException}. However, you can and
* should create tiered phasers to accommodate arbitrarily large sets
* of participants.
*
@@ -184,63 +226,49 @@ public class Phaser {
*/
/**
- * Barrier state representation. Conceptually, a barrier contains
- * four values:
+ * Primary state representation, holding four fields:
*
- * * 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
*/
@@ -252,65 +280,167 @@ public class Phaser {
*/
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 the number of parties
- * required to trip the barrier in future phases. If this phaser
+ * 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 also arrives at and is deregistered
- * from its parent.
+ * 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
+ * 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 awaitAdvance
- * method. If instead you need to deregister upon arrival use
- * {@code arriveAndDeregister}.
+ * 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
*/
public int arriveAndAwaitAdvance() {
- return awaitAdvance(arrive());
+ return awaitAdvance(doArrive(ONE_ARRIVAL));
}
/**
- * Awaits the phase of the barrier to advance from the given phase
- * value, or returns immediately if current phase of the barrier
- * is not equal to the given phase value or this barrier is
- * terminated.
+ * 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 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 {@code arriveAndDeregister}.
+ * @return the next arrival phase number, or a negative value
+ * if terminated or argument is negative
*/
public int awaitAdvance(int phase) {
+ Phaser rt;
+ 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)((rt = root).state >>> PHASE_SHIFT)) == phase)
+ return rt.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 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 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 {@code arriveAndDeregister}.
+ * @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 rt;
+ 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)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = rt.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 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 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 rt;
+ 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)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = rt.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 phaser 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;
}
}
@@ -629,16 +708,18 @@ public class Phaser {
/**
* 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.
+ * 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 phaseOf(getReconciledState());
+ return (int)(root.state >>> PHASE_SHIFT);
}
/**
- * Returns the number of parties registered at this barrier.
+ * Returns the number of parties registered at this phaser.
*
* @return the number of parties
*/
@@ -647,23 +728,28 @@ 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 phaser.
*
* @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());
}
/**
* Returns the number of registered parties that have not yet
- * arrived at the current phase of this barrier.
+ * arrived at the current phase of this 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());
}
/**
@@ -686,41 +772,56 @@ public class Phaser {
}
/**
- * Returns {@code true} if this barrier has been terminated.
+ * Returns {@code true} if this phaser has been terminated.
*
- * @return {@code true} if this barrier has been terminated
+ * @return {@code true} if this phaser 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 {@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.
- *
- * The default version returns {@code 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 {@link #awaitAdvance} at each phase.
- * Otherwise, you cannot ensure lack of interference from other
- * parties during the the invocation of 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 advancing this phaser (when all other
+ * waiting parties are dormant). If this method returns {@code
+ * true}, then, rather than advance the phase number, this phaser
+ * 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 advance this phaser, 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 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 barrier should terminate
+ * @return {@code true} if this phaser should terminate
*/
protected boolean onAdvance(int phase, int registeredParties) {
- return registeredParties <= 0;
+ return registeredParties == 0;
}
/**
@@ -730,192 +831,178 @@ public class Phaser {
* followed by the number of registered parties, and {@code
* "arrived = "} followed by the number of arrived parties.
*
- * @return a string identifying this barrier, as well as its state
+ * @return a string identifying this phaser, 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
/**
- * Wait nodes for Treiber stack representing wait queue
+ * Removes and signals threads from queue for phase.
*/
- static final class QNode implements ForkJoinPool.ManagedBlocker {
- final Phaser phaser;
- final int phase;
- final long startTime;
- final long nanos;
- final boolean timed;
- final boolean interruptible;
- volatile boolean wasInterrupted = false;
- volatile Thread thread; // nulled to cancel wait
- QNode next;
- QNode(Phaser phaser, int phase, boolean interruptible,
- boolean timed, long startTime, long nanos) {
- this.phaser = phaser;
- this.phase = phase;
- this.timed = timed;
- this.interruptible = interruptible;
- this.startTime = startTime;
- this.nanos = nanos;
- thread = Thread.currentThread();
- }
- public boolean isReleasable() {
- return (thread == null ||
- phaser.getPhase() != phase ||
- (interruptible && wasInterrupted) ||
- (timed && (nanos - (System.nanoTime() - startTime)) <= 0));
- }
- public boolean block() {
- if (Thread.interrupted()) {
- wasInterrupted = true;
- if (interruptible)
- return true;
- }
- if (!timed)
- LockSupport.park(this);
- else {
- long waitTime = nanos - (System.nanoTime() - startTime);
- if (waitTime <= 0)
- return true;
- LockSupport.parkNanos(this, waitTime);
- }
- return isReleasable();
- }
- void signal() {
- Thread t = thread;
- if (t != null) {
- thread = null;
+ private void releaseWaiters(int phase) {
+ QNode q; // first element of queue
+ int p; // its phase
+ Thread t; // its thread
+ AtomicReference