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}. As illustrated below, when + *
Termination. A phaser may enter a termination + * 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. * - *
Tiering. Phasers may be tiered (i.e., arranged - * in tree structures) to reduce contention. Phasers with large - * numbers of parties that would otherwise experience heavy + *
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. * + *
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. + * *
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 @@ -109,9 +122,9 @@ import java.util.concurrent.locks.LockSu *
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 tasks) {
@@ -142,14 +155,14 @@ import java.util.concurrent.locks.LockSu
* }
* };
* phaser.register();
- * for (Runnable task : tasks) {
+ * for (final Runnable task : tasks) {
* phaser.register();
* new Thread() {
* public void run() {
* do {
* task.run();
* phaser.arriveAndAwaitAdvance();
- * } while(!phaser.isTerminated();
+ * } while (!phaser.isTerminated());
* }
* }.start();
* }
@@ -158,61 +171,55 @@ import java.util.concurrent.locks.LockSu
*
* If the main task must later await termination, it
* may re-register and then execute a similar loop:
- * {@code
+ * {@code
* // ...
* phaser.register();
* while (!phaser.isTerminated())
- * phaser.arriveAndAwaitAdvance();
- * }
+ * phaser.arriveAndAwaitAdvance();}
*
- * Related constructions may be used to await particular phase numbers
+ * 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();
+ * {@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:
+ *
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:
+ *
*
{@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[] 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)
- * actions[i] = new Task(b);
- * // assumes new Task(b) performs b.register()
+ * tasks[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 {@code IllegalStateException}. However, you can and
@@ -230,60 +237,68 @@ 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)
- *
- * 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.
+ * Primary state representation, holding four fields:
*
- * Note: there are some cheats in arrive() that rely on unarrived
- * count being lowest 16 bits.
+ * * 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 with 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. Method reconcileState
+ * is usually attempted only only when the number of unarrived
+ * parties appears to be zero, which indicates a potential lag in
+ * updating phase after the root advanced.
*/
private volatile long state;
- 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 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 EMPTY = 1;
+
+ // The following unpacking methods are usually manually inlined
private static int unarrivedOf(long s) {
- return (int) (s & ushortMask);
+ int counts = (int)s;
+ return (counts == EMPTY) ? 0 : counts & 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");
+ int counts = (int)s;
+ return (counts == EMPTY) ? 0 :
+ (counts >>> PARTIES_SHIFT) - (counts & UNARRIVED_MASK);
}
/**
@@ -292,70 +307,177 @@ public class Phaser {
private final Phaser parent;
/**
- * The root of phaser tree. Equals this if not in a tree. Used to
- * support faster state push-down.
+ * The root of phaser tree. Equals this if not in a tree.
*/
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(false);
}
/**
- * 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. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * 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() {
- // 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(true);
}
/**
- * 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}. It is an unenforced usage error
- * for an unregistered party to invoke this method.
+ * 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
+ * @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() {
- return awaitAdvance(arrive());
+ // 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);
+ int counts = (int)s;
+ int unarrived = (counts & UNARRIVED_MASK) - 1;
+ if (phase < 0)
+ return phase;
+ else if (counts == EMPTY || unarrived < 0) {
+ if (reconcileState() == s)
+ throw new IllegalStateException(badArrive(s));
+ }
+ else if (UNSAFE.compareAndSwapLong(this, stateOffset, s,
+ s -= ONE_ARRIVAL)) {
+ if (unarrived != 0)
+ 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 (!UNSAFE.compareAndSwapLong(this, stateOffset, s, n))
+ return (int)(state >>> PHASE_SHIFT); // terminated
+ releaseWaiters(phase);
+ return nextPhase;
+ }
+ }
}
/**
- * 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. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * 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 its variants
- * @return the next arrival phase number, or a negative value
- * if terminated or argument is negative
+ * 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;
+ int p = (int)((root == this? state : reconcileState()) >>> 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)
+ return root.internalAwaitAdvance(phase, null);
+ return p;
}
/**
- * Awaits the phase of the barrier to advance from the given phase
+ * 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 of
- * the barrier is not equal to the given phase value or this
- * barrier is terminated. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * 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 its variants
- * @return the next arrival phase number, or a negative value
- * if terminated or argument is negative
+ * 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;
+ int p = (int)((root == this? state : reconcileState()) >>> 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) {
+ 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 the barrier to advance from the given phase
+ * 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 of the barrier is
- * not equal to the given phase value or this barrier is
- * terminated. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * 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 its variants
+ * 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
+ * @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;
+ int p = (int)((root == this? state : reconcileState()) >>> 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) {
+ 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 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
+ * 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() {
- 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))) {
+ // Only need to change root state
+ final Phaser root = this.root;
+ long s;
+ while ((s = root.state) >= 0) {
+ long next = (s & ~((long)UNARRIVED_MASK)) | TERMINATION_BIT;
+ if (UNSAFE.compareAndSwapLong(root, stateOffset, s, next)) {
+ // signal all threads
releaseWaiters(0);
releaseWaiters(1);
- if (parent != null)
- parent.forceTermination();
return;
}
}
@@ -696,16 +786,18 @@ 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
*/
@@ -715,22 +807,22 @@ public class Phaser {
/**
* Returns the number of registered parties that have arrived at
- * the current phase of this barrier.
+ * the current phase of this phaser.
*
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(state);
+ return 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);
+ return unarrivedOf(reconcileState());
}
/**
@@ -753,50 +845,56 @@ 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 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.
+ * 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.
*
* The arguments to this method provide the state of the phaser
- * prevailing for the current transition. (When called from within
- * an implementation of {@code onAdvance} the values returned by
- * methods such as {@code getPhase} may or may not reliably
- * indicate the state to which this transition applies.)
- *
- * 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 invocation of this method.
+ * 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;
}
/**
@@ -806,192 +904,200 @@ 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
+ Thread t; // its thread
+ AtomicReference