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 @@ -76,11 +76,13 @@ 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 @@ -95,7 +97,7 @@ import java.util.concurrent.locks.LockSu * 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
@@ -240,15 +242,15 @@ public class Phaser {
*/
private volatile long state;
- 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;
- private static final long PARTIES_MASK = 0xffff0000L; // for masking long
- 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
@@ -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.
@@ -304,12 +322,14 @@ public class Phaser {
private int doArrive(long adj) {
for (;;) {
long s = state;
+ int unarrived = (int)s & UNARRIVED_MASK;
int phase = (int)(s >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- int unarrived = (int)s & UNARRIVED_MASK;
- if (unarrived == 0)
- checkBadArrive(s);
+ 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
@@ -320,7 +340,7 @@ public class Phaser {
final Phaser parent = this.parent;
if (parent == null) {
if (onAdvance(phase, u))
- next |= TERMINATION_PHASE; // obliterate phase
+ next |= TERMINATION_BIT;
UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
releaseWaiters(phase);
}
@@ -340,17 +360,6 @@ public class Phaser {
}
/**
- * Rechecks state and throws bounds exceptions on arrival -- called
- * only if unarrived is apparently zero.
- */
- private void checkBadArrive(long s) {
- if (reconcileState() == s)
- throw new IllegalStateException
- ("Attempted arrival of unregistered party for " +
- stateToString(s));
- }
-
- /**
* Implementation of register, bulkRegister
*
* @param registrations number to add to both parties and
@@ -366,24 +375,34 @@ public class Phaser {
int phase = (int)(s >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- else if (parties != 0 && ((int)s & UNARRIVED_MASK) == 0)
- internalAwaitAdvance(phase, null); // wait for onAdvance
else if (registrations > MAX_PARTIES - parties)
throw new IllegalStateException(badRegister(s));
- else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
- return phase;
+ 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;
+ }
+ }
+ }
+ }
}
}
/**
- * Returns message string for out of bounds exceptions on registration.
- */
- private String badRegister(long s) {
- return "Attempt to register more than " +
- MAX_PARTIES + " parties for " + stateToString(s);
- }
-
- /**
* Recursively resolves lagged phase propagation from root if necessary.
*/
private long reconcileState() {
@@ -400,10 +419,7 @@ public class Phaser {
long u = s & PARTIES_MASK; // reset unarrived to parties
long next = ((((long) rPhase) << PHASE_SHIFT) | u |
(u >>> PARTIES_SHIFT));
- if (state == s &&
- UNSAFE.compareAndSwapLong(this, stateOffset,
- s, s = next))
- break;
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
}
s = state;
}
@@ -412,16 +428,16 @@ public class Phaser {
}
/**
- * 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
@@ -435,30 +451,25 @@ public class 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. If the number of
- * parties is zero, the parent phaser will not proceed until this
- * child phaser registers parties and advances, or this child
- * phaser deregisters with its parent, or the parent is otherwise
- * terminated. This child Phaser will be deregistered from its
- * parent automatically upon any invocation of the child's {@link
- * #arriveAndDeregister} method that results in the child's number
- * of registered parties becoming zero. (Although rarely
- * appropriate, this child may also explicity deregister from its
- * parent using {@code getParent().arriveAndDeregister()}.) After
- * deregistration, the child cannot re-register. (Instead, you can
- * create a new child 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
@@ -466,29 +477,30 @@ public class Phaser {
public Phaser(Phaser parent, int parties) {
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.doRegister(1);
+ 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
@@ -499,9 +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
@@ -518,10 +533,12 @@ public class Phaser {
}
/**
- * 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
@@ -533,12 +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
@@ -554,8 +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
@@ -578,11 +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;
- long s = (parent == null) ? state : reconcileState();
- int p = (int)(s >>> PHASE_SHIFT);
- return (p != phase) ? p : internalAwaitAdvance(phase, null);
+ if (p == phase &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase)
+ return r.internalAwaitAdvance(phase, null);
+ return p;
}
/**
@@ -601,13 +629,14 @@ public class Phaser {
*/
public int awaitAdvanceInterruptibly(int phase)
throws InterruptedException {
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = (parent == null) ? state : reconcileState();
- int p = (int)(s >>> PHASE_SHIFT);
- if (p == phase) {
+ if (p == phase &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
QNode node = new QNode(this, phase, true, false, 0L);
- p = internalAwaitAdvance(phase, node);
+ p = r.internalAwaitAdvance(phase, node);
if (node.wasInterrupted)
throw new InterruptedException();
}
@@ -637,14 +666,15 @@ public class Phaser {
public int awaitAdvanceInterruptibly(int phase,
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
+ Phaser r;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = (parent == null) ? state : reconcileState();
- int p = (int)(s >>> PHASE_SHIFT);
- if (p == phase) {
- long nanos = unit.toNanos(timeout);
+ if (p == phase &&
+ (p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
QNode node = new QNode(this, phase, true, true, nanos);
- p = internalAwaitAdvance(phase, node);
+ p = r.internalAwaitAdvance(phase, node);
if (node.wasInterrupted)
throw new InterruptedException();
else if (p == phase)
@@ -655,9 +685,9 @@ public class Phaser {
/**
* 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
+ * 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.
@@ -668,7 +698,7 @@ public class Phaser {
long s;
while ((s = root.state) >= 0) {
if (UNSAFE.compareAndSwapLong(root, stateOffset,
- s, s | TERMINATION_PHASE)) {
+ s, s | TERMINATION_BIT)) {
releaseWaiters(0); // signal all threads
releaseWaiters(1);
return;
@@ -703,7 +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());
}
/**
@@ -713,23 +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;
@@ -756,7 +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
@@ -766,10 +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
@@ -780,7 +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
@@ -839,6 +882,7 @@ public class Phaser {
/**
* Possibly blocks and waits for phase to advance unless aborted.
+ * Call only from root node.
*
* @param phase current phase
* @param node if non-null, the wait node to track interrupt and timeout;
@@ -846,14 +890,12 @@ public class Phaser {
* @return current phase
*/
private int internalAwaitAdvance(int phase, QNode node) {
- Phaser current = this; // to eventually wait at root if tiered
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) {
- Phaser par;
+ while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) {
int unarrived = (int)s & UNARRIVED_MASK;
if (unarrived != lastUnarrived) {
if (lastUnarrived == -1) // ensure old queue clean
@@ -861,11 +903,6 @@ public class Phaser {
if ((lastUnarrived = unarrived) < NCPU)
spins += SPINS_PER_ARRIVAL;
}
- else if (unarrived == 0 && (par = current.parent) != null) {
- current = par; // if all arrived, use parent
- par = par.parent;
- lastUnarrived = -1;
- }
else if (spins > 0) {
if (--spins == (SPINS_PER_ARRIVAL >>> 1))
Thread.yield(); // yield midway through spin
@@ -873,17 +910,15 @@ public class Phaser {
else if (node == null) // must be noninterruptible
node = new QNode(this, phase, false, false, 0L);
else if (node.isReleasable()) {
- if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
- break;
- else
- return phase; // aborted
+ 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)(root.state >>> PHASE_SHIFT)) != phase)
+ if ((p = (int)(state >>> PHASE_SHIFT)) != phase)
break; // recheck to avoid stale enqueue
else
queued = head.compareAndSet(q, node);
@@ -897,9 +932,15 @@ public class Phaser {
}
}
}
- releaseWaiters(phase);
- if (node != null)
- node.onRelease();
+
+ if (node != null) {
+ if (node.thread != null)
+ node.thread = null; // disable unpark() in node.signal
+ if (!node.interruptible && node.wasInterrupted)
+ Thread.currentThread().interrupt();
+ }
+ if (p != phase)
+ releaseWaiters(phase);
return p;
}
@@ -972,14 +1013,6 @@ public class Phaser {
LockSupport.unpark(t);
}
}
-
- void onRelease() { // actions upon return from internalAwaitAdvance
- if (!interruptible && wasInterrupted)
- Thread.currentThread().interrupt();
- if (thread != null)
- thread = null;
- }
-
}
// Unsafe mechanics