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 - * 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 + *
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., + * 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
@@ -117,7 +130,7 @@ import java.util.concurrent.locks.LockSu
* void runTasks(List 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:
+ * 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:
*
* Implementation notes: This implementation restricts the
@@ -224,48 +237,68 @@ public class Phaser {
*/
/**
- * Barrier state representation. Conceptually, a barrier contains
- * four values:
+ * Primary state representation, holding four bit-fields:
*
- * * unarrived -- the number of parties yet to hit barrier (bits 0-15)
- * * parties -- the number of parties to wait (bits 16-31)
- * * phase -- the generation of the barrier (bits 32-62)
- * * terminated -- set if barrier is terminated (bit 63 / sign)
- *
- * 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.
+ * unarrived -- the number of parties yet to hit barrier (bits 0-15)
+ * parties -- the number of parties to wait (bits 16-31)
+ * phase -- the generation of the barrier (bits 32-62)
+ * terminated -- set if barrier is terminated (bit 63 / sign)
+ *
+ * Except that a phaser with no registered parties is
+ * distinguished by the otherwise illegal state of having zero
+ * parties and one unarrived parties (encoded as EMPTY below).
+ *
+ * To efficiently maintain atomicity, these values are packed into
+ * a single (atomic) long. Good performance relies on keeping
+ * state decoding and encoding simple, and keeping race windows
+ * short.
+ *
+ * All state updates are performed via CAS except initial
+ * registration of a sub-phaser (i.e., one with a non-null
+ * parent). In this (relatively rare) case, we use built-in
+ * synchronization to lock while first registering with its
+ * parent.
+ *
+ * The phase of a subphaser is allowed to lag that of its
+ * ancestors until it is actually accessed -- see method
+ * reconcileState.
*/
private volatile long state;
- private static final int MAX_COUNT = 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 long UNARRIVED_MASK = 0xffffL;
- private static final long PARTIES_MASK = 0xffff0000L;
- private static final long ONE_ARRIVAL = 1L;
- private static final long ONE_PARTY = 1L << PARTIES_SHIFT;
- private static final long TERMINATION_PHASE = -1L << PHASE_SHIFT;
+ private static final int MAX_PARTIES = 0xffff;
+ private static final int MAX_PHASE = Integer.MAX_VALUE;
+ private static final int PARTIES_SHIFT = 16;
+ private static final int PHASE_SHIFT = 32;
+ private static final int UNARRIVED_MASK = 0xffff; // to mask ints
+ private static final long PARTIES_MASK = 0xffff0000L; // to mask longs
+ private static final long COUNTS_MASK = 0xffffffffL;
+ private static final long TERMINATION_BIT = 1L << 63;
+
+ // some special values
+ private static final int ONE_ARRIVAL = 1;
+ private static final int ONE_PARTY = 1 << PARTIES_SHIFT;
+ private static final int ONE_DEREGISTER = ONE_ARRIVAL|ONE_PARTY;
+ private static final int EMPTY = 1;
// The following unpacking methods are usually manually inlined
private static int unarrivedOf(long s) {
- return (int) (s & UNARRIVED_MASK);
+ int counts = (int)s;
+ return (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
}
private static int partiesOf(long s) {
- return ((int) (s & PARTIES_MASK)) >>> PARTIES_SHIFT;
+ return (int)s >>> PARTIES_SHIFT;
}
private static int phaseOf(long s) {
- return (int) (s >>> PHASE_SHIFT);
+ return (int)(s >>> PHASE_SHIFT);
}
private static int arrivedOf(long s) {
- return partiesOf(s) - unarrivedOf(s);
+ int counts = (int)s;
+ return (counts == EMPTY) ? 0 :
+ (counts >>> PARTIES_SHIFT) - (counts & UNARRIVED_MASK);
}
/**
@@ -274,8 +307,7 @@ 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;
@@ -293,128 +325,160 @@ public class Phaser {
}
/**
+ * Returns message string for bounds exceptions on arrival.
+ */
+ private String badArrive(long s) {
+ return "Attempted arrival of unregistered party for " +
+ stateToString(s);
+ }
+
+ /**
+ * Returns message string for bounds exceptions on registration.
+ */
+ private String badRegister(long s) {
+ return "Attempt to register more than " +
+ MAX_PARTIES + " parties for " + stateToString(s);
+ }
+
+ /**
* Main implementation for methods arrive and arriveAndDeregister.
* Manually tuned to speed up and minimize race windows for the
* common case of just decrementing unarrived field.
*
- * @param adj - adjustment to apply to state -- either
- * ONE_ARRIVAL (for arrive) or
- * ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
- */
- private int doArrive(long adj) {
- long s;
- int phase, unarrived;
- while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0) {
- if ((unarrived = (int)(s & UNARRIVED_MASK)) != 0) {
- if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s -= adj)) {
- if (unarrived == 1) {
- Phaser par;
- long p = s & PARTIES_MASK; // unshifted parties field
- long lu = p >>> PARTIES_SHIFT;
- int u = (int)lu;
+ * @param adjust value to subtract from state;
+ * ONE_ARRIVAL for arrive,
+ * ONE_DEREGISTER for arriveAndDeregister
+ */
+ private int doArrive(int adjust) {
+ final Phaser root = this.root;
+ for (;;) {
+ long s = (root == this) ? state : reconcileState();
+ int phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0)
+ return phase;
+ int counts = (int)s;
+ int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
+ if (unarrived <= 0)
+ throw new IllegalStateException(badArrive(s));
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adjust)) {
+ if (unarrived == 1) {
+ long n = s & PARTIES_MASK; // base of next state
+ int nextUnarrived = (int)n >>> PARTIES_SHIFT;
+ if (root == this) {
+ if (onAdvance(phase, nextUnarrived))
+ n |= TERMINATION_BIT;
+ else if (nextUnarrived == 0)
+ n |= EMPTY;
+ else
+ n |= nextUnarrived;
int nextPhase = (phase + 1) & MAX_PHASE;
- long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
- if ((par = parent) == null) {
- UNSAFE.compareAndSwapLong
- (this, stateOffset, s, onAdvance(phase, u)?
- next | TERMINATION_PHASE : next);
- releaseWaiters(phase);
- }
- else {
- par.doArrive(u == 0?
- ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
- if ((int)(par.state >>> PHASE_SHIFT) != nextPhase ||
- ((int)(state >>> PHASE_SHIFT) != nextPhase &&
- !UNSAFE.compareAndSwapLong(this, stateOffset,
- s, next)))
- reconcileState();
- }
+ n |= (long)nextPhase << PHASE_SHIFT;
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
+ releaseWaiters(phase);
}
- break;
+ else if (nextUnarrived == 0) { // propagate deregistration
+ phase = parent.doArrive(ONE_DEREGISTER);
+ UNSAFE.compareAndSwapLong(this, stateOffset,
+ s, s | EMPTY);
+ }
+ else
+ phase = parent.doArrive(ONE_ARRIVAL);
}
+ return phase;
}
- else if (state == s && reconcileState() == s) // recheck
- throw new IllegalStateException(badArrive());
}
- return phase;
- }
-
- /**
- * Returns message string for bounds exceptions on arrival.
- * Declared out of-line from doArrive to reduce string op bulk.
- */
- private String badArrive() {
- return ("Attempted arrival of unregistered party for " +
- this.toString());
}
/**
* Implementation of register, bulkRegister
*
- * @param registrations number to add to both parties and unarrived fields
+ * @param registrations number to add to both parties and
+ * unarrived fields. Must be greater than zero.
*/
private int doRegister(int registrations) {
- long adj = (long)registrations; // adjustment to state
- adj |= adj << PARTIES_SHIFT;
- Phaser par = parent;
- long s;
+ // adjustment to state
+ long adjust = ((long)registrations << PARTIES_SHIFT) | registrations;
+ final Phaser parent = this.parent;
int phase;
- while ((phase = (int)((s = (par == null? state : reconcileState()))
- >>> PHASE_SHIFT)) >= 0) {
- int parties = ((int)(s & PARTIES_MASK)) >>> PARTIES_SHIFT;
- if (parties != 0 && (s & UNARRIVED_MASK) == 0)
- internalAwaitAdvance(phase, null); // wait for onAdvance
- else if (parties + registrations > MAX_COUNT)
- throw new IllegalStateException(badRegister());
- else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
+ for (;;) {
+ long s = (parent == null) ? state : reconcileState();
+ int counts = (int)s;
+ int parties = counts >>> PARTIES_SHIFT;
+ int unarrived = counts & UNARRIVED_MASK;
+ if (registrations > MAX_PARTIES - parties)
+ throw new IllegalStateException(badRegister(s));
+ phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0)
break;
+ if (counts != EMPTY) { // not 1st registration
+ if (parent == null || reconcileState() == s) {
+ if (unarrived == 0) // wait out advance
+ root.internalAwaitAdvance(phase, null);
+ else if (UNSAFE.compareAndSwapLong(this, stateOffset,
+ s, s + adjust))
+ break;
+ }
+ }
+ else if (parent == null) { // 1st root registration
+ long next = ((long)phase << PHASE_SHIFT) | adjust;
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
+ break;
+ }
+ else {
+ synchronized (this) { // 1st sub registration
+ if (state == s) { // recheck under lock
+ phase = parent.doRegister(1);
+ if (phase < 0)
+ break;
+ // finish registration whenever parent registration
+ // succeeded, even when racing with termination,
+ // since these are part of the same "transaction".
+ while (!UNSAFE.compareAndSwapLong
+ (this, stateOffset, s,
+ ((long)phase << PHASE_SHIFT) | adjust)) {
+ s = state;
+ phase = (int)(root.state >>> PHASE_SHIFT);
+ // assert (int)s == EMPTY;
+ }
+ break;
+ }
+ }
+ }
}
return phase;
}
/**
- * Returns message string for bounds exceptions on registration
- */
- private String badRegister() {
- return ("Attempt to register more than " + MAX_COUNT + " parties for "+
- this.toString());
- }
-
- /**
- * Recursively resolves lagged phase propagation from root if
- * necessary.
+ * Resolves lagged phase propagation from root if necessary.
+ * Reconciliation normally occurs when root has advanced but
+ * subphasers have not yet done so, in which case they must finish
+ * their own advance by setting unarrived to parties (or if
+ * parties is zero, resetting to unregistered EMPTY state).
+ *
+ * @return reconciled state
*/
private long reconcileState() {
- Phaser par = parent;
- if (par == null)
- return state;
- Phaser rt = root;
- long s;
- int phase, rPhase;
- while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0 &&
- (rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
- if (rPhase < 0 || (s & UNARRIVED_MASK) == 0) {
- long ps = par.parent == null? par.state : par.reconcileState();
- int pPhase = (int)(ps >>> PHASE_SHIFT);
- if (pPhase < 0 || pPhase == ((phase + 1) & MAX_PHASE)) {
- if (state != s)
- continue;
- long p = s & PARTIES_MASK;
- long next = ((((long) pPhase) << PHASE_SHIFT) |
- (p >>> PARTIES_SHIFT) | p);
- if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
- return next;
- }
- }
- if (state == s)
- releaseWaiters(phase); // help release others
+ final Phaser root = this.root;
+ long s = state;
+ if (root != this) {
+ int phase, p;
+ // CAS to root phase with current parties, tripping unarrived
+ while ((phase = (int)(root.state >>> PHASE_SHIFT)) !=
+ (int)(s >>> PHASE_SHIFT) &&
+ !UNSAFE.compareAndSwapLong
+ (this, stateOffset, s,
+ s = (((long)phase << PHASE_SHIFT) |
+ ((phase < 0) ? (s & COUNTS_MASK) :
+ (((p = (int)s >>> PARTIES_SHIFT) == 0) ? EMPTY :
+ ((s & PARTIES_MASK) | p))))))
+ s = state;
}
return s;
}
/**
- * Creates a new phaser without any initially registered parties,
- * initial phase number 0, and no parent. Any thread using this
+ * Creates a new phaser with no initially registered parties, no
+ * parent, and initial phase number 0. Any thread using this
* phaser will need to first register for it.
*/
public Phaser() {
@@ -423,9 +487,10 @@ public class Phaser {
/**
* Creates a new phaser with the given number of registered
- * unarrived parties, initial phase number 0, and no parent.
+ * unarrived parties, no parent, and initial phase number 0.
*
- * @param parties the number of parties required to trip barrier
+ * @param parties the number of parties required to advance to the
+ * next phase
* @throws IllegalArgumentException if parties less than zero
* or greater than the maximum number of parties supported
*/
@@ -434,10 +499,7 @@ public class Phaser {
}
/**
- * Creates a new phaser with the given parent, without any
- * initially registered parties. If parent is non-null this phaser
- * is registered with the parent and its initial phase number is
- * the same as that of parent phaser.
+ * Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
*
* @param parent the parent phaser
*/
@@ -447,43 +509,52 @@ public class Phaser {
/**
* Creates a new phaser with the given parent and number of
- * registered unarrived parties. If parent is non-null, this phaser
- * is registered with the parent and its initial phase number is
- * the same as that of parent phaser.
+ * registered unarrived parties. When the given parent is non-null
+ * and the given number of parties is greater than zero, this
+ * child phaser is registered with its parent.
*
* @param parent the parent phaser
- * @param parties the number of parties required to trip barrier
+ * @param parties the number of parties required to advance to the
+ * next phase
* @throws IllegalArgumentException if parties less than zero
* or greater than the maximum number of parties supported
*/
public Phaser(Phaser parent, int parties) {
- if (parties < 0 || parties > MAX_COUNT)
+ if (parties >>> PARTIES_SHIFT != 0)
throw new IllegalArgumentException("Illegal number of parties");
- int phase;
+ int phase = 0;
this.parent = parent;
if (parent != null) {
- Phaser r = parent.root;
- this.root = r;
- this.evenQ = r.evenQ;
- this.oddQ = r.oddQ;
- phase = parent.register();
+ final Phaser root = parent.root;
+ this.root = root;
+ this.evenQ = root.evenQ;
+ this.oddQ = root.oddQ;
+ if (parties != 0)
+ phase = parent.doRegister(1);
}
else {
this.root = this;
this.evenQ = new AtomicReference 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
@@ -527,106 +606,150 @@ public class Phaser {
}
/**
- * 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() {
- return doArrive(ONE_ARRIVAL|ONE_PARTY);
+ return doArrive(ONE_DEREGISTER);
}
/**
- * 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 {@code
* awaitAdvance} method. If instead you need to deregister upon
- * arrival, use {@link #arriveAndDeregister}. It is an unenforced
- * usage error for an unregistered party to invoke this method.
+ * arrival, use {@code awaitAdvance(arriveAndDeregister())}.
*
- * @return the arrival phase number, or a negative number 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 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);
+ if (phase < 0)
+ return phase;
+ int counts = (int)s;
+ int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
+ if (unarrived <= 0)
+ throw new IllegalStateException(badArrive(s));
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s,
+ s -= ONE_ARRIVAL)) {
+ if (unarrived > 1)
+ return root.internalAwaitAdvance(phase, null);
+ if (root != this)
+ return parent.arriveAndAwaitAdvance();
+ long n = s & PARTIES_MASK; // base of next state
+ int nextUnarrived = (int)n >>> PARTIES_SHIFT;
+ if (onAdvance(phase, nextUnarrived))
+ n |= TERMINATION_BIT;
+ else if (nextUnarrived == 0)
+ n |= EMPTY;
+ else
+ n |= nextUnarrived;
+ int nextPhase = (phase + 1) & MAX_PHASE;
+ n |= (long)nextPhase << PHASE_SHIFT;
+ if (!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.
+ * 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;
+ long s = (root == this) ? state : reconcileState();
+ int p = (int)(s >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
- if (p != phase)
- return p;
- return internalAwaitAdvance(phase, null);
+ 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.
+ * 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;
+ long s = (root == this) ? state : reconcileState();
+ int p = (int)(s >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
- if (p != phase)
- return p;
- QNode node = new QNode(this, phase, true, false, 0L);
- p = internalAwaitAdvance(phase, node);
- if (node.wasInterrupted)
- throw new InterruptedException();
- else
- return p;
+ 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.
+ * 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
*/
@@ -634,76 +757,88 @@ public class Phaser {
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
long nanos = unit.toNanos(timeout);
+ final Phaser root = this.root;
+ long s = (root == this) ? state : reconcileState();
+ int p = (int)(s >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
- if (p != phase)
- return p;
- QNode node = new QNode(this, phase, true, true, nanos);
- p = internalAwaitAdvance(phase, node);
- if (node.wasInterrupted)
- throw new InterruptedException();
- else if (p == phase)
- throw new TimeoutException();
- else
- return p;
+ 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() {
- Phaser r = root; // force at root then reconcile
+ // Only need to change root state
+ final Phaser root = this.root;
long s;
- while ((s = r.state) >= 0)
- UNSAFE.compareAndSwapLong(r, stateOffset, s, s | TERMINATION_PHASE);
- reconcileState();
- releaseWaiters(0); // signal all threads
- releaseWaiters(1);
+ while ((s = root.state) >= 0) {
+ if (UNSAFE.compareAndSwapLong(root, stateOffset,
+ s, s | TERMINATION_BIT)) {
+ // signal all threads
+ releaseWaiters(0); // Waiters on evenQ
+ releaseWaiters(1); // Waiters on oddQ
+ return;
+ }
+ }
}
/**
* Returns the current phase number. The maximum phase number is
* {@code Integer.MAX_VALUE}, after which it restarts at
- * zero. Upon termination, the phase number is negative.
+ * zero. Upon termination, the phase number is negative,
+ * in which case the prevailing phase prior to termination
+ * may be obtained via {@code getPhase() + Integer.MIN_VALUE}.
*
* @return the phase number, or a negative value if terminated
*/
public final int getPhase() {
- return (int)((parent == null? state : reconcileState()) >>> PHASE_SHIFT);
+ 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
*/
public int getRegisteredParties() {
- return partiesOf(parent == null? state : reconcileState());
+ return partiesOf(state);
}
/**
* Returns the number of registered parties that have arrived at
- * the current phase of this barrier.
+ * the current phase of this phaser. If this phaser has terminated,
+ * the returned value is meaningless and arbitrary.
*
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(parent == null? state : reconcileState());
+ 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. If this phaser has
+ * terminated, the returned value is meaningless and arbitrary.
*
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(parent == null? state : reconcileState());
+ return unarrivedOf(reconcileState());
}
/**
@@ -726,47 +861,56 @@ 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 (parent == null? state : reconcileState()) < 0;
+ return root.state < 0L;
}
/**
* Overridable method to perform an action upon impending phase
* advance, and to control termination. This method is invoked
- * upon arrival of the party tripping the barrier (when all other
+ * 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 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.
+ * 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. The effects of invoking
- * arrival, registration, and waiting methods on this Phaser from
+ * 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
+ * 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.
*
- * 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.
+ * 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
- * void build(Task[] actions, int lo, int hi, Phaser ph) {
+ * 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(actions, i, j, new Phaser(ph));
+ * build(tasks, i, j, new Phaser(ph));
* }
* } else {
* for (int i = lo; i < hi; ++i)
- * actions[i] = new Task(ph);
+ * 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.
*
* {@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;
}
/**
@@ -776,43 +920,63 @@ 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 = reconcileState();
+ return stateToString(reconcileState());
+ }
+
+ /**
+ * Implementation of toString and string-based error messages
+ */
+ private String stateToString(long s) {
return super.toString() +
"[phase = " + phaseOf(s) +
" parties = " + partiesOf(s) +
" arrived = " + arrivedOf(s) + "]";
}
+ // Waiting mechanics
+
/**
- * Removes and signals threads from queue for phase
+ * Removes and signals threads from queue for phase.
*/
private void releaseWaiters(int phase) {
- AtomicReference