Registration. Unlike the case for other barriers, the - * number of parties registered to synchronize on a phaser + * 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 @@ -76,26 +76,28 @@ import java.util.concurrent.locks.LockSu * *
Termination. A {@code Phaser} may enter a * termination state in which all synchronization methods - * immediately return without updating phaser state or waiting for + * 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 + * 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. * *
Monitoring. While synchronization methods may be invoked - * only by registered parties, the current state of a phaser may be + * 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 @@ -181,9 +183,9 @@ import java.util.concurrent.locks.LockSu * }} * * - *
To create a set of tasks using a tree of phasers, + *
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 + * Task class with a constructor accepting a Phaser that * it registers with upon construction: * *
{@code
@@ -210,7 +212,7 @@ import java.util.concurrent.locks.LockSu
* 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
- * should create tiered phasers to accommodate arbitrarily large sets
+ * should create tiered Phasers to accommodate arbitrarily large sets
* of participants.
*
* @since 1.7
@@ -240,24 +242,24 @@ public class Phaser {
*/
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 = 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 & UNARRIVED_MASK);
+ return (int)s & 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) {
@@ -293,6 +295,22 @@ 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.
@@ -302,127 +320,124 @@ public class Phaser {
* 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;
- 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();
- }
+ for (;;) {
+ long s = state;
+ int unarrived = (int)s & UNARRIVED_MASK;
+ int phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0)
+ return phase;
+ else if (unarrived == 0) {
+ if (reconcileState() == s) // recheck
+ throw new IllegalStateException(badArrive(s));
+ }
+ else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
+ if (unarrived == 1) {
+ long p = s & PARTIES_MASK; // unshifted parties field
+ long lu = p >>> PARTIES_SHIFT;
+ int u = (int)lu;
+ int nextPhase = (phase + 1) & MAX_PHASE;
+ long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
+ final Phaser parent = this.parent;
+ if (parent == null) {
+ if (onAdvance(phase, u))
+ next |= TERMINATION_BIT;
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
+ releaseWaiters(phase);
+ }
+ else {
+ parent.doArrive((u == 0) ?
+ ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
+ if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase ||
+ ((int)(state >>> PHASE_SHIFT) != nextPhase &&
+ !UNSAFE.compareAndSwapLong(this, stateOffset,
+ s, next)))
+ reconcileState();
}
- break;
}
+ 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;
- 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))
- break;
+ // adjustment to state
+ long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
+ final Phaser parent = this.parent;
+ for (;;) {
+ long s = (parent == null) ? state : reconcileState();
+ int parties = (int)s >>> PARTIES_SHIFT;
+ int phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0)
+ return phase;
+ else if (registrations > MAX_PARTIES - parties)
+ throw new IllegalStateException(badRegister(s));
+ else if ((parties == 0 && parent == null) || // first reg of root
+ ((int)s & UNARRIVED_MASK) != 0) { // not advancing
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
+ return phase;
+ }
+ else if (parties != 0) // wait for onAdvance
+ root.internalAwaitAdvance(phase, null);
+ else { // 1st registration of child
+ synchronized(this) { // register parent first
+ if (reconcileState() == s) { // recheck under lock
+ parent.doRegister(1); // OK if throws IllegalState
+ for (;;) { // simpler form of outer loop
+ s = reconcileState();
+ phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0 ||
+ UNSAFE.compareAndSwapLong(this, stateOffset,
+ s, s + adj))
+ return phase;
+ }
+ }
+ }
+ }
}
- 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.
+ * Recursively resolves lagged phase propagation from root if necessary.
*/
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;
+ long s = state;
+ if (par != null) {
+ Phaser rt = root;
+ int phase, rPhase;
+ while ((phase = (int)(s >>> PHASE_SHIFT)) >= 0 &&
+ (rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
+ if ((int)(par.state >>> PHASE_SHIFT) != rPhase)
+ par.reconcileState();
+ else if (rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) {
+ long u = s & PARTIES_MASK; // reset unarrived to parties
+ long next = ((((long) rPhase) << PHASE_SHIFT) | u |
+ (u >>> PARTIES_SHIFT));
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
}
+ s = state;
}
- if (state == s)
- releaseWaiters(phase); // help release others
}
return s;
}
/**
- * Creates a new phaser without any initially registered parties,
+ * Creates a new Phaser without any initially registered parties,
* initial phase number 0, and no parent. Any thread using this
- * phaser will need to first register for it.
+ * Phaser will need to first register for it.
*/
public Phaser() {
this(null, 0);
}
/**
- * Creates a new phaser with the given number of registered
+ * Creates a new Phaser with the given number of registered
* unarrived parties, initial phase number 0, and no parent.
*
* @param parties the number of parties required to trip barrier
@@ -434,54 +449,58 @@ 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
+ * @param parent the parent Phaser
*/
public Phaser(Phaser parent) {
this(parent, 0);
}
/**
- * 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.
+ * Creates a new Phaser with the given parent and number of
+ * registered unarrived parties. Registration and deregistration
+ * of this child Phaser with its parent are managed automatically.
+ * If the given parent is non-null, whenever this child Phaser has
+ * any registered parties (as established in this constructor,
+ * {@link #register}, or {@link #bulkRegister}), this child Phaser
+ * is registered with its parent. Whenever the number of
+ * registered parties becomes zero as the result of an invocation
+ * of {@link #arriveAndDeregister}, this child Phaser is
+ * deregistered from its parent.
*
- * @param parent the parent phaser
+ * @param parent the parent Phaser
* @param parties the number of parties required to trip barrier
* @throws IllegalArgumentException if parties less than zero
* or greater than the maximum number of parties supported
*/
public 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;
+ long s = ((long) parties) | (((long) parties) << PARTIES_SHIFT);
this.parent = parent;
if (parent != null) {
Phaser r = parent.root;
this.root = r;
this.evenQ = r.evenQ;
this.oddQ = r.oddQ;
- phase = parent.register();
+ if (parties != 0)
+ s |= ((long)(parent.doRegister(1))) << PHASE_SHIFT;
}
else {
this.root = this;
this.evenQ = new AtomicReference();
this.oddQ = new AtomicReference();
- phase = 0;
}
- long p = (long)parties;
- this.state = (((long) phase) << PHASE_SHIFT) | p | (p << PARTIES_SHIFT);
+ this.state = s;
}
/**
- * Adds a new unarrived party to this phaser.
- * If an ongoing invocation of {@link #onAdvance} is in progress,
- * this method may wait until its completion before registering.
+ * Adds a new unarrived party to this Phaser. If an ongoing
+ * invocation of {@link #onAdvance} is in progress, this method
+ * may await its completion before returning. If this Phaser has
+ * a parent, and this Phaser previously had no registered parties,
+ * this Phaser is also registered with its parent.
*
* @return the arrival phase number to which this registration applied
* @throws IllegalStateException if attempting to register more
@@ -492,9 +511,12 @@ public class Phaser {
}
/**
- * Adds the given number of new unarrived parties to this phaser.
+ * Adds the given number of new unarrived parties to this Phaser.
* If an ongoing invocation of {@link #onAdvance} is in progress,
- * this method may wait until its completion before registering.
+ * this method may await its completion before returning. If this
+ * Phaser has a parent, and the given number of parities is
+ * greater than zero, and this Phaser previously had no registered
+ * parties, this Phaser is also registered with its parent.
*
* @param parties the number of additional parties required to trip barrier
* @return the arrival phase number to which this registration applied
@@ -505,18 +527,18 @@ public class Phaser {
public int bulkRegister(int parties) {
if (parties < 0)
throw new IllegalArgumentException();
- if (parties > MAX_COUNT)
- throw new IllegalStateException(badRegister());
if (parties == 0)
return getPhase();
return doRegister(parties);
}
/**
- * Arrives at the barrier, but does not wait for others. (You can
- * in turn wait for others via {@link #awaitAdvance}). It is an
- * unenforced usage error for an unregistered party to invoke this
- * method.
+ * Arrives at the barrier, without waiting for others to arrive.
+ *
+ * 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
@@ -528,12 +550,16 @@ 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
- * 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.
+ * for others to arrive. Deregistration reduces the number of
+ * parties required to trip the barrier in future phases. If this
+ * Phaser has a parent, and deregistration causes this Phaser to
+ * have zero parties, this Phaser is also deregistered from its
+ * parent.
+ *
+ *
It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this Phaser, if ever.
*
* @return the arrival phase number, or a negative value if terminated
* @throws IllegalStateException if not terminated and the number
@@ -549,8 +575,12 @@ public class Phaser {
* 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())}.
+ *
+ *
It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this Phaser, if ever.
*
* @return the arrival phase number, or a negative number if terminated
* @throws IllegalStateException if not terminated and the number
@@ -573,12 +603,14 @@ public class Phaser {
* if terminated or argument is negative
*/
public int awaitAdvance(int phase) {
+ Phaser r;
+ int p = (int)(state >>> 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 &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase)
+ return r.internalAwaitAdvance(phase, null);
+ return p;
}
/**
@@ -597,17 +629,18 @@ public class Phaser {
*/
public int awaitAdvanceInterruptibly(int phase)
throws InterruptedException {
+ Phaser r;
+ int p = (int)(state >>> 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 &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = r.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ }
+ return p;
}
/**
@@ -634,36 +667,43 @@ public class Phaser {
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
long nanos = unit.toNanos(timeout);
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- 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 &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = r.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else if (p == phase)
+ throw new TimeoutException();
+ }
+ return p;
}
/**
- * Forces this barrier to enter termination state. Counts of
- * arrived and registered parties are unaffected. If this phaser
- * has a parent, it too is terminated. This method may be useful
- * for coordinating recovery after one or more tasks encounter
- * unexpected exceptions.
+ * Forces this barrier to enter termination state. Counts of
+ * arrived and registered parties are unaffected. If this Phaser
+ * is a member of a tiered set of Phasers, then all of the Phasers
+ * in the set are terminated. If this Phaser is already
+ * terminated, this method has no effect. This method may be
+ * useful for coordinating recovery after one or more tasks
+ * encounter unexpected exceptions.
*/
public void forceTermination() {
- 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)) {
+ releaseWaiters(0); // signal all threads
+ releaseWaiters(1);
+ return;
+ }
+ }
}
/**
@@ -674,7 +714,7 @@ public class Phaser {
* @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);
}
/**
@@ -683,7 +723,7 @@ public class Phaser {
* @return the number of parties
*/
public int getRegisteredParties() {
- return partiesOf(parent == null? state : reconcileState());
+ return partiesOf(state);
}
/**
@@ -693,7 +733,11 @@ public class Phaser {
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(parent == null? state : reconcileState());
+ long s = state;
+ int u = unarrivedOf(s); // only reconcile if possibly needed
+ return (u != 0 || parent == null) ?
+ partiesOf(s) - u :
+ arrivedOf(reconcileState());
}
/**
@@ -703,23 +747,24 @@ public class Phaser {
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(parent == null? state : reconcileState());
+ int u = unarrivedOf(state);
+ return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
}
/**
- * Returns the parent of this phaser, or {@code null} if none.
+ * Returns the parent of this Phaser, or {@code null} if none.
*
- * @return the parent of this phaser, or {@code null} if none
+ * @return the parent of this Phaser, or {@code null} if none
*/
public Phaser getParent() {
return parent;
}
/**
- * Returns the root ancestor of this phaser, which is the same as
- * this phaser if it has no parent.
+ * Returns the root ancestor of this Phaser, which is the same as
+ * this Phaser if it has no parent.
*
- * @return the root ancestor of this phaser
+ * @return the root ancestor of this Phaser
*/
public Phaser getRoot() {
return root;
@@ -731,7 +776,7 @@ public class Phaser {
* @return {@code true} if this barrier has been terminated
*/
public boolean isTerminated() {
- return (parent == null? state : reconcileState()) < 0;
+ return root.state < 0L;
}
/**
@@ -746,7 +791,7 @@ public class Phaser {
* propagated to the party attempting to trip the barrier, in
* which case no advance occurs.
*
- *
The arguments to this method provide the state of the phaser
+ *
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
@@ -756,10 +801,18 @@ public class Phaser {
* {@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
+ * Phaser phaser = new Phaser() {
+ * protected boolean onAdvance(int phase, int parties) { return false; }
+ * }}
*
* @param phase the phase number on entering the barrier
* @param registeredParties the current number of registered parties
@@ -770,7 +823,7 @@ public class Phaser {
}
/**
- * Returns a string identifying this phaser, as well as its
+ * Returns a string identifying this Phaser, as well as its
* state. The state, in brackets, includes the String {@code
* "phase = "} followed by the phase number, {@code "parties = "}
* followed by the number of registered parties, and {@code
@@ -779,15 +832,23 @@ public class Phaser {
* @return a string identifying this barrier, 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 head = queueFor(phase);
@@ -801,20 +862,6 @@ public class Phaser {
}
}
- /**
- * Tries to enqueue given node in the appropriate wait queue.
- *
- * @return true if successful
- */
- private boolean tryEnqueue(int phase, QNode node) {
- releaseWaiters(phase-1); // ensure old queue clean
- AtomicReference head = queueFor(phase);
- QNode q = head.get();
- return ((q == null || q.phase == phase) &&
- (int)(root.state >>> PHASE_SHIFT) == phase &&
- head.compareAndSet(node.next = q, node));
- }
-
/** The number of CPUs, for spin control */
private static final int NCPU = Runtime.getRuntime().availableProcessors();
@@ -826,46 +873,57 @@ public class Phaser {
* avoid it when threads regularly arrive: When a thread in
* internalAwaitAdvance notices another arrival before blocking,
* and there appear to be enough CPUs available, it spins
- * SPINS_PER_ARRIVAL more times before continuing to try to
- * block. The value trades off good-citizenship vs big unnecessary
- * slowdowns.
+ * SPINS_PER_ARRIVAL more times before blocking. Plus, even on
+ * uniprocessors, there is at least one intervening Thread.yield
+ * before blocking. The value trades off good-citizenship vs big
+ * unnecessary slowdowns.
*/
- static final int SPINS_PER_ARRIVAL = NCPU < 2? 1 : 1 << 8;
+ static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
/**
* Possibly blocks and waits for phase to advance unless aborted.
+ * Call only from root node.
*
* @param phase current phase
- * @param node if nonnull, the wait node to track interrupt and timeout;
+ * @param node if non-null, the wait node to track interrupt and timeout;
* if null, denotes noninterruptible wait
* @return current phase
*/
private int internalAwaitAdvance(int phase, QNode node) {
- Phaser current = this; // to eventually wait at root if tiered
- Phaser par = parent;
- boolean queued = false;
- int spins = SPINS_PER_ARRIVAL;
+ boolean queued = false; // true when node is enqueued
int lastUnarrived = -1; // to increase spins upon change
+ int spins = SPINS_PER_ARRIVAL;
long s;
int p;
- while ((p = (int)((s = current.state) >>> PHASE_SHIFT)) == phase) {
- int unarrived = (int)(s & UNARRIVED_MASK);
+ while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) {
+ int unarrived = (int)s & UNARRIVED_MASK;
if (unarrived != lastUnarrived) {
+ if (lastUnarrived == -1) // ensure old queue clean
+ releaseWaiters(phase-1);
if ((lastUnarrived = unarrived) < NCPU)
spins += SPINS_PER_ARRIVAL;
}
- else if (unarrived == 0 && par != null) {
- current = par; // if all arrived, use parent
- par = par.parent;
- }
- else if (spins > 0)
- --spins;
- else if (node == null)
+ else if (spins > 0) {
+ if (--spins == (SPINS_PER_ARRIVAL >>> 1))
+ Thread.yield(); // yield midway through spin
+ }
+ else if (node == null) // must be noninterruptible
node = new QNode(this, phase, false, false, 0L);
- else if (node.isReleasable())
- break;
- else if (!queued)
- queued = tryEnqueue(phase, node);
+ else if (node.isReleasable()) {
+ p = (int)(state >>> PHASE_SHIFT);
+ break; // aborted
+ }
+ else if (!queued) { // push onto queue
+ AtomicReference head = queueFor(phase);
+ QNode q = head.get();
+ if (q == null || q.phase == phase) {
+ node.next = q;
+ if ((p = (int)(state >>> PHASE_SHIFT)) != phase)
+ break; // recheck to avoid stale enqueue
+ else
+ queued = head.compareAndSet(q, node);
+ }
+ }
else {
try {
ForkJoinPool.managedBlock(node);
@@ -874,14 +932,13 @@ public class Phaser {
}
}
}
+
if (node != null) {
if (node.thread != null)
- node.thread = null;
+ node.thread = null; // disable unpark() in node.signal
if (!node.interruptible && node.wasInterrupted)
Thread.currentThread().interrupt();
}
- if (p == phase)
- p = (int)(reconcileState() >>> PHASE_SHIFT);
if (p != phase)
releaseWaiters(phase);
return p;