src/share/classes/java/util/concurrent/Phaser.java
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@@ -33,10 +33,12 @@
* http://creativecommons.org/licenses/publicdomain
*/
package java.util.concurrent;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.LockSupport;
/**
* A reusable synchronization barrier, similar in functionality to
@@ -59,65 +61,67 @@
*
* <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code
* Phaser} may be repeatedly awaited. Method {@link
* #arriveAndAwaitAdvance} has effect analogous to {@link
* java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each
- * generation of a {@code Phaser} has an associated phase number. The
- * phase number starts at zero, and advances when all parties arrive
- * at the barrier, wrapping around to zero after reaching {@code
+ * generation of a phaser has an associated phase number. The phase
+ * number starts at zero, and advances when all parties arrive at the
+ * phaser, wrapping around to zero after reaching {@code
* Integer.MAX_VALUE}. The use of phase numbers enables independent
- * control of actions upon arrival at a barrier and upon awaiting
+ * control of actions upon arrival at a phaser and upon awaiting
* others, via two kinds of methods that may be invoked by any
* registered party:
*
* <ul>
*
* <li> <b>Arrival.</b> Methods {@link #arrive} and
- * {@link #arriveAndDeregister} record arrival at a
- * barrier. These methods do not block, but return an associated
- * <em>arrival phase number</em>; that is, the phase number of
- * the barrier to which the arrival applied. When the final
- * party for a given phase arrives, an optional barrier action
- * is performed and the phase advances. Barrier actions,
- * performed by the party triggering a phase advance, are
- * arranged by overriding method {@link #onAdvance(int, int)},
- * which also controls termination. Overriding this method is
- * similar to, but more flexible than, providing a barrier
- * action to a {@code CyclicBarrier}.
+ * {@link #arriveAndDeregister} record arrival. These methods
+ * do not block, but return an associated <em>arrival phase
+ * number</em>; that is, the phase number of the phaser to which
+ * the arrival applied. When the final party for a given phase
+ * arrives, an optional action is performed and the phase
+ * advances. These actions are performed by the party
+ * triggering a phase advance, and are arranged by overriding
+ * method {@link #onAdvance(int, int)}, which also controls
+ * termination. Overriding this method is similar to, but more
+ * flexible than, providing a barrier action to a {@code
+ * CyclicBarrier}.
*
* <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an
* argument indicating an arrival phase number, and returns when
- * the barrier advances to (or is already at) a different phase.
+ * the phaser advances to (or is already at) a different phase.
* Unlike similar constructions using {@code CyclicBarrier},
* method {@code awaitAdvance} continues to wait even if the
* waiting thread is interrupted. Interruptible and timeout
* versions are also available, but exceptions encountered while
* tasks wait interruptibly or with timeout do not change the
- * state of the barrier. If necessary, you can perform any
+ * state of the phaser. If necessary, you can perform any
* associated recovery within handlers of those exceptions,
* often after invoking {@code forceTermination}. Phasers may
* also be used by tasks executing in a {@link ForkJoinPool},
* which will ensure sufficient parallelism to execute tasks
* when others are blocked waiting for a phase to advance.
*
* </ul>
*
- * <p> <b>Termination.</b> A {@code Phaser} may enter a
- * <em>termination</em> 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.
+ * <p> <b>Termination.</b> A phaser may enter a <em>termination</em>
+ * state in which all synchronization methods immediately return
+ * without updating phaser state or waiting for advance, and
+ * indicating (via a negative phase value) that execution is complete.
+ * Termination is triggered when an invocation of {@code onAdvance}
+ * returns {@code true}. The default implementation returns {@code
+ * true} if a deregistration has caused the number of registered
+ * parties to become zero. As illustrated below, when phasers control
+ * actions with a fixed number of iterations, it is often convenient
+ * to override this method to cause termination when the current phase
+ * number reaches a threshold. Method {@link #forceTermination} is
+ * also available to abruptly release waiting threads and allow them
+ * to terminate.
*
- * <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., arranged
- * in tree structures) to reduce contention. Phasers with large
- * numbers of parties that would otherwise experience heavy
+ * <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (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.
*
@@ -134,13 +138,13 @@
* informal monitoring.
*
* <p><b>Sample usages:</b>
*
* <p>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:
*
* <pre> {@code
* void runTasks(List<Runnable> tasks) {
* final Phaser phaser = new Phaser(1); // "1" to register self
* // create and start threads
@@ -208,12 +212,12 @@
* }}</pre>
*
*
* <p>To create a set of tasks using a tree of phasers,
* you could use code of the following form, assuming a
- * Task class with a constructor accepting a phaser that
- * it registers for upon construction:
+ * Task class with a constructor accepting a {@code Phaser} that
+ * it registers with upon construction:
*
* <pre> {@code
* void build(Task[] actions, int lo, int hi, Phaser ph) {
* if (hi - lo > TASKS_PER_PHASER) {
* for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
@@ -228,16 +232,14 @@
* }
* // .. initially called, for n tasks via
* build(new Task[n], 0, n, new Phaser());}</pre>
*
* 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.
*
- * </pre>
- *
* <p><b>Implementation notes</b>: 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
* of participants.
@@ -251,67 +253,54 @@
* Vijay Saraswat for the idea, and to Vivek Sarkar for
* enhancements to extend functionality.
*/
/**
- * Barrier state representation. Conceptually, a barrier contains
- * four values:
+ * Primary state representation, holding four fields:
*
- * * parties -- the number of parties to wait (16 bits)
- * * unarrived -- the number of parties yet to hit barrier (16 bits)
- * * phase -- the generation of the barrier (31 bits)
- * * terminated -- set if barrier is terminated (1 bit)
+ * * unarrived -- the number of parties yet to hit barrier (bits 0-15)
+ * * parties -- the number of parties to wait (bits 16-31)
+ * * phase -- the generation of the barrier (bits 32-62)
+ * * terminated -- set if barrier is terminated (bit 63 / sign)
*
* However, to efficiently maintain atomicity, these values are
* packed into a single (atomic) long. Termination uses the sign
* bit of 32 bit representation of phase, so phase is set to -1 on
* termination. Good performance relies on keeping state decoding
* and encoding simple, and keeping race windows short.
- *
- * Note: there are some cheats in arrive() that rely on unarrived
- * count being lowest 16 bits.
*/
private volatile long state;
- private static final int ushortMask = 0xffff;
- private static final int phaseMask = 0x7fffffff;
+ private static final int MAX_PARTIES = 0xffff;
+ private static final int MAX_PHASE = 0x7fffffff;
+ private static final int PARTIES_SHIFT = 16;
+ private static final int PHASE_SHIFT = 32;
+ private static final int UNARRIVED_MASK = 0xffff; // to mask ints
+ private static final long PARTIES_MASK = 0xffff0000L; // to mask longs
+ private static final long ONE_ARRIVAL = 1L;
+ private static final long ONE_PARTY = 1L << PARTIES_SHIFT;
+ private static final long TERMINATION_BIT = 1L << 63;
+ // The following unpacking methods are usually manually inlined
+
private static int unarrivedOf(long s) {
- return (int) (s & ushortMask);
+ return (int)s & UNARRIVED_MASK;
}
private static int partiesOf(long s) {
- return ((int) s) >>> 16;
+ return (int)s >>> PARTIES_SHIFT;
}
private static int phaseOf(long s) {
- return (int) (s >>> 32);
+ return (int) (s >>> PHASE_SHIFT);
}
private static int arrivedOf(long s) {
return partiesOf(s) - unarrivedOf(s);
}
- private static long stateFor(int phase, int parties, int unarrived) {
- return ((((long) phase) << 32) | (((long) parties) << 16) |
- (long) unarrived);
- }
-
- private static long trippedStateFor(int phase, int parties) {
- long lp = (long) parties;
- return (((long) phase) << 32) | (lp << 16) | lp;
- }
-
/**
- * Returns message string for bad bounds exceptions.
- */
- private static String badBounds(int parties, int unarrived) {
- return ("Attempt to set " + unarrived +
- " unarrived of " + parties + " parties");
- }
-
- /**
* The parent of this phaser, or null if none
*/
private final Phaser parent;
/**
@@ -318,123 +307,232 @@
* The root of phaser tree. Equals this if not in a tree. Used to
* support faster state push-down.
*/
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<QNode> evenQ = new AtomicReference<QNode>();
- private final AtomicReference<QNode> oddQ = new AtomicReference<QNode>();
+ private final AtomicReference<QNode> evenQ;
+ private final AtomicReference<QNode> oddQ;
private AtomicReference<QNode> queueFor(int phase) {
return ((phase & 1) == 0) ? evenQ : oddQ;
}
/**
- * Returns current state, first resolving lagged propagation from
- * root if necessary.
+ * Returns message string for bounds exceptions on arrival.
*/
- private long getReconciledState() {
- return (parent == null) ? state : reconcileState();
+ private String badArrive(long s) {
+ return "Attempted arrival of unregistered party for " +
+ stateToString(s);
}
/**
- * Recursively resolves state.
+ * Returns message string for bounds exceptions on registration.
*/
- private long reconcileState() {
- Phaser p = parent;
+ 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) {
+ for (;;) {
long s = state;
- if (p != null) {
- while (unarrivedOf(s) == 0 && phaseOf(s) != phaseOf(root.state)) {
- long parentState = p.getReconciledState();
- int parentPhase = phaseOf(parentState);
- int phase = phaseOf(s = state);
- if (phase != parentPhase) {
- long next = trippedStateFor(parentPhase, partiesOf(s));
- if (casState(s, next)) {
+ 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);
- s = next;
}
+ else {
+ parent.doArrive((u == 0) ?
+ ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
+ if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase)
+ reconcileState();
+ else if (state == s)
+ UNSAFE.compareAndSwapLong(this, stateOffset, s,
+ next);
}
}
+ return phase;
}
+ }
+ }
+
+ /**
+ * Implementation of register, bulkRegister
+ *
+ * @param registrations number to add to both parties and
+ * unarrived fields. Must be greater than zero.
+ */
+ private int doRegister(int registrations) {
+ // 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;
+ }
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * Recursively resolves lagged phase propagation from root if necessary.
+ */
+ private long reconcileState() {
+ Phaser par = parent;
+ 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 (par != rt && (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;
+ }
+ }
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() {
- this(null);
+ this(null, 0);
}
/**
- * Creates a new phaser with the given numbers of registered
- * unarrived parties, initial phase number 0, and no parent.
+ * Creates a new phaser with the given number of registered
+ * 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
*/
public Phaser(int parties) {
this(null, parties);
}
/**
- * 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
*/
public Phaser(Phaser parent) {
- int phase = 0;
- this.parent = parent;
- if (parent != null) {
- this.root = parent.root;
- phase = parent.register();
+ this(parent, 0);
}
- else
- this.root = this;
- this.state = trippedStateFor(phase, 0);
- }
/**
- * Creates a new phaser with the given parent and numbers 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 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 > ushortMask)
+ if (parties >>> PARTIES_SHIFT != 0)
throw new IllegalArgumentException("Illegal number of parties");
- int phase = 0;
+ long s = ((long) parties) | (((long) parties) << PARTIES_SHIFT);
this.parent = parent;
if (parent != null) {
- this.root = parent.root;
- phase = parent.register();
+ Phaser r = parent.root;
+ this.root = r;
+ this.evenQ = r.evenQ;
+ this.oddQ = r.oddQ;
+ if (parties != 0)
+ s |= ((long)(parent.doRegister(1))) << PHASE_SHIFT;
}
- else
+ else {
this.root = this;
- this.state = trippedStateFor(phase, parties);
+ this.evenQ = new AtomicReference<QNode>();
+ this.oddQ = new AtomicReference<QNode>();
}
+ this.state = s;
+ }
/**
- * Adds a new unarrived party to this phaser.
+ * 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
* than the maximum supported number of parties
*/
@@ -442,15 +540,22 @@
return doRegister(1);
}
/**
* Adds the given number of new unarrived parties 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 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 parties required to trip barrier
+ * @param parties the number of additional parties required to
+ * advance to the next phase
* @return the arrival phase number to which this registration applied
* @throws IllegalStateException if attempting to register more
* than the maximum supported number of parties
+ * @throws IllegalArgumentException if {@code parties < 0}
*/
public int bulkRegister(int parties) {
if (parties < 0)
throw new IllegalArgumentException();
if (parties == 0)
@@ -457,220 +562,128 @@
return getPhase();
return doRegister(parties);
}
/**
- * Shared code for register, bulkRegister
- */
- private int doRegister(int registrations) {
- int phase;
- for (;;) {
- long s = getReconciledState();
- phase = phaseOf(s);
- int unarrived = unarrivedOf(s) + registrations;
- int parties = partiesOf(s) + registrations;
- if (phase < 0)
- break;
- if (parties > ushortMask || unarrived > ushortMask)
- throw new IllegalStateException(badBounds(parties, unarrived));
- if (phase == phaseOf(root.state) &&
- casState(s, stateFor(phase, parties, unarrived)))
- break;
- }
- return phase;
- }
-
- /**
- * 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 this phaser, without waiting for others to arrive.
*
+ * <p>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;
+ return doArrive(ONE_ARRIVAL);
}
- 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;
- }
/**
- * 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.
*
+ * <p>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();
+ return doArrive(ONE_ARRIVAL|ONE_PARTY);
}
- 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;
- }
/**
- * 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())}.
*
+ * <p>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
* of unarrived parties would become negative
*/
public int arriveAndAwaitAdvance() {
- return awaitAdvance(arrive());
+ return awaitAdvance(doArrive(ONE_ARRIVAL));
}
/**
- * Awaits the phase of the barrier to advance from the given phase
- * value, 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
+ * previous call to {@code arrive} or {@code arriveAndDeregister}.
* @return the next arrival phase number, or a negative value
* if terminated or argument is negative
*/
public int awaitAdvance(int phase) {
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
+ return rt.internalAwaitAdvance(phase, null);
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);
}
/**
- * 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
+ * previous call to {@code arrive} or {@code arriveAndDeregister}.
* @return the next arrival phase number, or a negative value
* if terminated or argument is negative
* @throws InterruptedException if thread interrupted while waiting
*/
public int awaitAdvanceInterruptibly(int phase)
throws InterruptedException {
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = rt.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ }
return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase);
- return interruptibleWait(phase);
}
/**
- * 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
@@ -679,83 +692,95 @@
* @throws TimeoutException if timed out while waiting
*/
public int awaitAdvanceInterruptibly(int phase,
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = rt.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else if (p == phase)
+ throw new TimeoutException();
+ }
return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase, timeout, unit);
- return timedWait(phase, unit.toNanos(timeout));
}
/**
- * Forces this barrier to enter termination state. Counts of
+ * Forces this phaser 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.
+ * is a member of a tiered set of phasers, then all of the phasers
+ * in the set are terminated. If this phaser is already
+ * terminated, this method has no effect. This method may be
+ * useful for coordinating recovery after one or more tasks
+ * encounter unexpected exceptions.
*/
public void forceTermination() {
- for (;;) {
- long s = getReconciledState();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s);
- if (phase < 0 ||
- casState(s, stateFor(-1, parties, unarrived))) {
- releaseWaiters(0);
+ // Only need to change root state
+ final Phaser root = this.root;
+ long s;
+ while ((s = root.state) >= 0) {
+ if (UNSAFE.compareAndSwapLong(root, stateOffset,
+ s, s | TERMINATION_BIT)) {
+ releaseWaiters(0); // signal all threads
releaseWaiters(1);
- if (parent != null)
- parent.forceTermination();
return;
}
}
}
/**
* 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
*/
public int getRegisteredParties() {
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.
*
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(state);
+ long s = state;
+ int u = unarrivedOf(s); // only reconcile if possibly needed
+ return (u != 0 || parent == null) ?
+ partiesOf(s) - u :
+ arrivedOf(reconcileState());
}
/**
* Returns the number of registered parties that have not yet
- * arrived at the current phase of this barrier.
+ * arrived at the current phase of this phaser.
*
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(state);
+ int u = unarrivedOf(state);
+ return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
}
/**
* Returns the parent of this phaser, or {@code null} if none.
*
@@ -774,263 +799,249 @@
public Phaser getRoot() {
return root;
}
/**
- * 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 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
+ * true}, then, rather than advance the phase number, this phaser
* will be set to a final termination state, and subsequent calls
* to {@link #isTerminated} will return true. Any (unchecked)
* Exception or Error thrown by an invocation of this method is
- * propagated to the party attempting to trip the barrier, in
+ * propagated to the party attempting to advance this phaser, in
* which case no advance occurs.
*
* <p>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.)
+ * 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.
*
- * <p>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.
+ * <p>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.
*
- * <p>You may override this method to perform an action with side
- * effects visible to participating tasks, but it is 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. Additionally,
- * method {@code onAdvance} may be invoked more than once per
- * transition if registrations are intermixed with arrivals.
+ * <p>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}:
*
- * @param phase the phase number on entering the barrier
+ * <pre> {@code
+ * Phaser phaser = new Phaser() {
+ * protected boolean onAdvance(int phase, int parties) { return false; }
+ * }}</pre>
+ *
+ * @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;
}
/**
* 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
* "arrived = "} followed by the number of arrived parties.
*
- * @return a string identifying this barrier, as well as its state
+ * @return a string identifying this phaser, as well as its state
*/
public String toString() {
- long s = getReconciledState();
+ return stateToString(reconcileState());
+ }
+
+ /**
+ * Implementation of toString and string-based error messages
+ */
+ private String stateToString(long s) {
return super.toString() +
"[phase = " + phaseOf(s) +
" parties = " + partiesOf(s) +
" arrived = " + arrivedOf(s) + "]";
}
- // methods for waiting
+ // Waiting mechanics
/**
- * Wait nodes for Treiber stack representing wait queue
+ * Removes and signals threads from queue for phase.
*/
- static final class QNode implements ForkJoinPool.ManagedBlocker {
- final Phaser phaser;
- final int phase;
- final long startTime;
- final long nanos;
- final boolean timed;
- final boolean interruptible;
- volatile boolean wasInterrupted = false;
- volatile Thread thread; // nulled to cancel wait
- QNode next;
- QNode(Phaser phaser, int phase, boolean interruptible,
- boolean timed, long startTime, long nanos) {
- this.phaser = phaser;
- this.phase = phase;
- this.timed = timed;
- this.interruptible = interruptible;
- this.startTime = startTime;
- this.nanos = nanos;
- thread = Thread.currentThread();
- }
- public boolean isReleasable() {
- return (thread == null ||
- phaser.getPhase() != phase ||
- (interruptible && wasInterrupted) ||
- (timed && (nanos - (System.nanoTime() - startTime)) <= 0));
- }
- public boolean block() {
- if (Thread.interrupted()) {
- wasInterrupted = true;
- if (interruptible)
- return true;
- }
- if (!timed)
- LockSupport.park(this);
- else {
- long waitTime = nanos - (System.nanoTime() - startTime);
- if (waitTime <= 0)
- return true;
- LockSupport.parkNanos(this, waitTime);
- }
- return isReleasable();
- }
- void signal() {
- Thread t = thread;
- if (t != null) {
- thread = null;
+ private void releaseWaiters(int phase) {
+ QNode q; // first element of queue
+ int p; // its phase
+ Thread t; // its thread
+ AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
+ while ((q = head.get()) != null &&
+ ((p = q.phase) == phase ||
+ (int)(root.state >>> PHASE_SHIFT) != p)) {
+ if (head.compareAndSet(q, q.next) &&
+ (t = q.thread) != null) {
+ q.thread = null;
LockSupport.unpark(t);
}
}
- boolean doWait() {
- if (thread != null) {
- try {
- ForkJoinPool.managedBlock(this);
- } catch (InterruptedException ie) {
}
- }
- return wasInterrupted;
- }
- }
+ /** The number of CPUs, for spin control */
+ private static final int NCPU = Runtime.getRuntime().availableProcessors();
/**
- * Removes and signals waiting threads from wait queue.
+ * The number of times to spin before blocking while waiting for
+ * advance, per arrival while waiting. On multiprocessors, fully
+ * blocking and waking up a large number of threads all at once is
+ * usually a very slow process, so we use rechargeable spins to
+ * 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 blocking. The value trades
+ * off good-citizenship vs big unnecessary slowdowns.
*/
- private void releaseWaiters(int phase) {
- AtomicReference<QNode> head = queueFor(phase);
- QNode q;
- while ((q = head.get()) != null) {
- if (head.compareAndSet(q, q.next))
- q.signal();
- }
- }
+ static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
/**
- * Tries to enqueue given node in the appropriate wait queue.
+ * Possibly blocks and waits for phase to advance unless aborted.
+ * Call only from root node.
*
- * @return true if successful
- */
- private boolean tryEnqueue(QNode node) {
- AtomicReference<QNode> head = queueFor(node.phase);
- return head.compareAndSet(node.next = head.get(), node);
- }
-
- /**
- * Enqueues node and waits unless aborted or signalled.
- *
+ * @param phase current phase
+ * @param node if non-null, the wait node to track interrupt and timeout;
+ * if null, denotes noninterruptible wait
* @return current phase
*/
- private int untimedWait(int phase) {
- QNode node = null;
- boolean queued = false;
- boolean interrupted = false;
+ private int internalAwaitAdvance(int phase, QNode node) {
+ releaseWaiters(phase-1); // ensure old queue clean
+ boolean queued = false; // true when node is enqueued
+ int lastUnarrived = 0; // to increase spins upon change
+ int spins = SPINS_PER_ARRIVAL;
+ long s;
int p;
- while ((p = getPhase()) == phase) {
- if (Thread.interrupted())
- interrupted = true;
- else if (node == null)
- node = new QNode(this, phase, false, false, 0, 0);
- else if (!queued)
- queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
+ while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) {
+ if (node == null) { // spinning in noninterruptible mode
+ int unarrived = (int)s & UNARRIVED_MASK;
+ if (unarrived != lastUnarrived &&
+ (lastUnarrived = unarrived) < NCPU)
+ spins += SPINS_PER_ARRIVAL;
+ boolean interrupted = Thread.interrupted();
+ if (interrupted || --spins < 0) { // need node to record intr
+ node = new QNode(this, phase, false, false, 0L);
+ node.wasInterrupted = interrupted;
}
- if (node != null)
- node.thread = null;
- releaseWaiters(phase);
- if (interrupted)
- Thread.currentThread().interrupt();
- return p;
}
+ else if (node.isReleasable()) // done or aborted
+ break;
+ else if (!queued) { // push onto queue
+ AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
+ QNode q = node.next = head.get();
+ if ((q == null || q.phase == phase) &&
+ (int)(state >>> PHASE_SHIFT) == phase) // avoid stale enq
+ queued = head.compareAndSet(q, node);
+ }
+ else {
+ try {
+ ForkJoinPool.managedBlock(node);
+ } catch (InterruptedException ie) {
+ node.wasInterrupted = true;
+ }
+ }
+ }
- /**
- * Interruptible version
- * @return current phase
- */
- private int interruptibleWait(int phase) throws InterruptedException {
- QNode node = null;
- boolean queued = false;
- boolean interrupted = false;
- int p;
- while ((p = getPhase()) == phase && !interrupted) {
- if (Thread.interrupted())
- interrupted = true;
- else if (node == null)
- node = new QNode(this, phase, true, false, 0, 0);
- else if (!queued)
- queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
+ if (node != null) {
+ if (node.thread != null)
+ node.thread = null; // avoid need for unpark()
+ if (node.wasInterrupted && !node.interruptible)
+ Thread.currentThread().interrupt();
+ if ((p = (int)(state >>> PHASE_SHIFT)) == phase)
+ return p; // recheck abort
}
- if (node != null)
- node.thread = null;
- if (p != phase || (p = getPhase()) != phase)
releaseWaiters(phase);
- if (interrupted)
- throw new InterruptedException();
return p;
}
/**
- * Timeout version.
- * @return current phase
+ * Wait nodes for Treiber stack representing wait queue
*/
- private int timedWait(int phase, long nanos)
- throws InterruptedException, TimeoutException {
- long startTime = System.nanoTime();
- QNode node = null;
- boolean queued = false;
- boolean interrupted = false;
- int p;
- while ((p = getPhase()) == phase && !interrupted) {
+ static final class QNode implements ForkJoinPool.ManagedBlocker {
+ final Phaser phaser;
+ final int phase;
+ final boolean interruptible;
+ final boolean timed;
+ boolean wasInterrupted;
+ long nanos;
+ long lastTime;
+ volatile Thread thread; // nulled to cancel wait
+ QNode next;
+
+ QNode(Phaser phaser, int phase, boolean interruptible,
+ boolean timed, long nanos) {
+ this.phaser = phaser;
+ this.phase = phase;
+ this.interruptible = interruptible;
+ this.nanos = nanos;
+ this.timed = timed;
+ this.lastTime = timed ? System.nanoTime() : 0L;
+ thread = Thread.currentThread();
+ }
+
+ public boolean isReleasable() {
+ if (thread == null)
+ return true;
+ if (phaser.getPhase() != phase) {
+ thread = null;
+ return true;
+ }
if (Thread.interrupted())
- interrupted = true;
- else if (nanos - (System.nanoTime() - startTime) <= 0)
- break;
- else if (node == null)
- node = new QNode(this, phase, true, true, startTime, nanos);
- else if (!queued)
- queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
+ wasInterrupted = true;
+ if (wasInterrupted && interruptible) {
+ thread = null;
+ return true;
}
- if (node != null)
- node.thread = null;
- if (p != phase || (p = getPhase()) != phase)
- releaseWaiters(phase);
- if (interrupted)
- throw new InterruptedException();
- if (p == phase)
- throw new TimeoutException();
- return p;
+ if (timed) {
+ if (nanos > 0L) {
+ long now = System.nanoTime();
+ nanos -= now - lastTime;
+ lastTime = now;
}
+ if (nanos <= 0L) {
+ thread = null;
+ return true;
+ }
+ }
+ return false;
+ }
+ public boolean block() {
+ if (isReleasable())
+ return true;
+ else if (!timed)
+ LockSupport.park(this);
+ else if (nanos > 0)
+ LockSupport.parkNanos(this, nanos);
+ return isReleasable();
+ }
+ }
+
// Unsafe mechanics
private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
private static final long stateOffset =
objectFieldOffset("state", Phaser.class);
- private final boolean casState(long cmp, long val) {
- return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
- }
-
private static long objectFieldOffset(String field, Class<?> klazz) {
try {
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
} catch (NoSuchFieldException e) {
// Convert Exception to corresponding Error