Registration. Unlike the case for other barriers, the + * 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 + * optionally deregistered upon any arrival (using {@link * #arriveAndDeregister}). As is the case with most basic * synchronization constructs, registration and deregistration affect * only internal counts; they do not establish any further internal - * bookkeeping, so tasks cannot query whether they are - * registered. (However, you can introduce such bookkeeping by - * subclassing this class.) - * - *
Synchronization. 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 + * Integer.MAX_VALUE}. The use of phase numbers enables independent + * control of actions upon arrival at a barrier and upon awaiting + * others, via two kinds of methods that may be invoked by any + * registered party: * *
Termination. A {@code Phaser} may enter a + * termination state in which all synchronization methods + * immediately return without updating phaser state or waiting for + * advance, and indicating (via a negative phase value) that execution + * is complete. Termination is triggered when an invocation of {@code + * onAdvance} returns {@code true}. As illustrated below, when + * phasers control actions with a fixed number of iterations, it is * often convenient to override this method to cause termination when * the current phase number reaches a threshold. Method {@link * #forceTermination} is also available to abruptly release waiting * threads and allow them to terminate. * - *
Tiering. Phasers may be tiered (i.e., arranged + * in tree structures) to reduce contention. Phasers with large * numbers of parties that would otherwise experience heavy - * synchronization contention costs may instead be arranged in trees. - * This will typically greatly increase throughput even though it - * incurs somewhat greater per-operation overhead. - * - *
Monitoring. While synchronization methods may be invoked + * only by registered parties, the current state of a phaser may be + * monitored by any caller. At any given moment there are {@link + * #getRegisteredParties} parties in total, of which {@link * #getArrivedParties} have arrived at the current phase ({@link - * #getPhase}). When the remaining {@link #getUnarrivedParties}) - * arrive, the phase advances. Method {@link #toString} returns - * snapshots of these state queries in a form convenient for + * #getPhase}). When the remaining ({@link #getUnarrivedParties}) + * parties arrive, the phase advances. The values returned by these + * methods may reflect transient states and so are not in general + * useful for synchronization control. Method {@link #toString} + * returns snapshots of these state queries in a form convenient for * informal monitoring. * - *
Sample usages: * *
A {@code Phaser} may be used instead of a {@code CountDownLatch} - * to control a one-shot action serving a variable number of - * parties. The typical idiom is for the method setting this up to - * first register, then start the actions, then deregister, as in: + * to control a one-shot action serving a variable number of parties. + * The typical idiom is for the method setting this up to first + * register, then start the actions, then deregister, as in: * *
{@code
* void runTasks(List tasks) {
@@ -131,43 +136,66 @@ import java.util.concurrent.locks.LockSu
* {@code
* void startTasks(List tasks, final int iterations) {
* final Phaser phaser = new Phaser() {
- * public boolean onAdvance(int phase, int registeredParties) {
+ * protected boolean onAdvance(int phase, int registeredParties) {
* return phase >= iterations || registeredParties == 0;
* }
* };
* phaser.register();
- * for (Runnable task : tasks) {
+ * for (final Runnable task : tasks) {
* phaser.register();
* new Thread() {
* public void run() {
* do {
* task.run();
* phaser.arriveAndAwaitAdvance();
- * } while(!phaser.isTerminated();
+ * } while (!phaser.isTerminated());
* }
* }.start();
* }
* phaser.arriveAndDeregister(); // deregister self, don't wait
* }}
*
+ * If the main task must later await termination, it
+ * may re-register and then execute a similar loop:
+ * {@code
+ * // ...
+ * phaser.register();
+ * while (!phaser.isTerminated())
+ * phaser.arriveAndAwaitAdvance();}
+ *
+ * Related constructions may be used to await particular phase numbers
+ * in contexts where you are sure that the phase will never wrap around
+ * {@code Integer.MAX_VALUE}. For example:
+ *
+ *
{@code
+ * void awaitPhase(Phaser phaser, int phase) {
+ * int p = phaser.register(); // assumes caller not already registered
+ * while (p < phase) {
+ * if (phaser.isTerminated())
+ * // ... deal with unexpected termination
+ * else
+ * p = phaser.arriveAndAwaitAdvance();
+ * }
+ * phaser.arriveAndDeregister();
+ * }}
+ *
+ *
* 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:
+ * it registers with upon construction:
+ *
*
{@code
- * void build(Task[] actions, int lo, int hi, Phaser b) {
- * int step = (hi - lo) / TASKS_PER_PHASER;
- * if (step > 1) {
- * int i = lo;
- * while (i < hi) {
- * int r = Math.min(i + step, hi);
- * build(actions, i, r, new Phaser(b));
- * i = r;
+ * void build(Task[] actions, int lo, int hi, Phaser ph) {
+ * if (hi - lo > TASKS_PER_PHASER) {
+ * for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
+ * int j = Math.min(i + TASKS_PER_PHASER, hi);
+ * build(actions, i, j, new Phaser(ph));
* }
* } else {
* for (int i = lo; i < hi; ++i)
- * actions[i] = new Task(b);
- * // assumes new Task(b) performs b.register()
+ * actions[i] = new Task(ph);
+ * // assumes new Task(ph) performs ph.register()
* }
* }
* // .. initially called, for n tasks via
@@ -178,8 +206,6 @@ import java.util.concurrent.locks.LockSu
* be appropriate for extremely small per-barrier task bodies (thus
* high rates), or up to hundreds for extremely large ones.
*
- *
- *
* Implementation notes: This implementation restricts the
* maximum number of parties to 65535. Attempts to register additional
* parties result in {@code IllegalStateException}. However, you can and
@@ -216,7 +242,6 @@ public class Phaser {
*/
private volatile long state;
- private static final int ushortBits = 16;
private static final int ushortMask = 0xffff;
private static final int phaseMask = 0x7fffffff;
@@ -269,11 +294,12 @@ public class Phaser {
/**
* 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 evenQ = new AtomicReference();
- private final AtomicReference oddQ = new AtomicReference();
+ private final AtomicReference evenQ;
+ private final AtomicReference oddQ;
private AtomicReference queueFor(int phase) {
return ((phase & 1) == 0) ? evenQ : oddQ;
@@ -291,20 +317,20 @@ public class Phaser {
* Recursively resolves state.
*/
private long reconcileState() {
- Phaser p = parent;
+ Phaser par = parent;
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) {
+ if (par != null) {
+ int phase, rootPhase;
+ while ((phase = phaseOf(s)) >= 0 &&
+ (rootPhase = phaseOf(root.state)) != phase &&
+ (rootPhase < 0 || unarrivedOf(s) == 0)) {
+ int parentPhase = phaseOf(par.getReconciledState());
+ if (parentPhase != phase) {
long next = trippedStateFor(parentPhase, partiesOf(s));
- if (casState(s, next)) {
- releaseWaiters(phase);
- s = next;
- }
+ if (state == s)
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
}
+ s = state;
}
}
return s;
@@ -316,11 +342,11 @@ public class Phaser {
* 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
+ * 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
@@ -340,19 +366,11 @@ public class Phaser {
* @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();
- }
- else
- this.root = this;
- this.state = trippedStateFor(phase, 0);
+ this(parent, 0);
}
/**
- * Creates a new phaser with the given parent and numbers of
+ * 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.
@@ -365,19 +383,28 @@ public class Phaser {
public Phaser(Phaser parent, int parties) {
if (parties < 0 || parties > ushortMask)
throw new IllegalArgumentException("Illegal number of parties");
- int phase = 0;
+ int phase;
this.parent = parent;
if (parent != null) {
- this.root = parent.root;
+ Phaser r = parent.root;
+ this.root = r;
+ this.evenQ = r.evenQ;
+ this.oddQ = r.oddQ;
phase = parent.register();
}
- else
+ else {
this.root = this;
+ this.evenQ = new AtomicReference();
+ this.oddQ = new AtomicReference();
+ phase = 0;
+ }
this.state = trippedStateFor(phase, parties);
}
/**
* 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.
*
* @return the arrival phase number to which this registration applied
* @throws IllegalStateException if attempting to register more
@@ -389,11 +416,14 @@ public class 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.
*
- * @param parties the number of parties required to trip barrier
+ * @param parties the number of additional parties required to trip barrier
* @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)
@@ -407,67 +437,65 @@ public class Phaser {
* Shared code for register, bulkRegister
*/
private int doRegister(int registrations) {
+ Phaser par = parent;
+ long s;
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)
+ while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
+ int p = partiesOf(s);
+ int u = unarrivedOf(s);
+ int unarrived = u + registrations;
+ int parties = p + registrations;
+ if (u == 0 && p != 0) // if tripped, wait for advance
+ untimedWait(phase);
+ else if (parties > ushortMask)
throw new IllegalStateException(badBounds(parties, unarrived));
- if (phase == phaseOf(root.state) &&
- casState(s, stateFor(phase, parties, unarrived)))
- break;
+ else if (par == null || phaseOf(root.state) == phase) {
+ long next = stateFor(phase, parties, unarrived);
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
+ break;
+ }
}
return phase;
}
/**
* Arrives at the barrier, but does not wait for others. (You can
- * in turn wait for others via {@link #awaitAdvance}).
+ * in turn wait for others via {@link #awaitAdvance}). It is an
+ * unenforced usage error for an unregistered party to invoke this
+ * method.
*
* @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() {
+ Phaser par = parent;
+ long s;
int phase;
- for (;;) {
- long s = state;
- phase = phaseOf(s);
- if (phase < 0)
- break;
+ while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
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;
+ if (unarrived > 0) { // Not the last arrival
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s - 1))
+ break; // s-1 adds 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 (unarrived < 0)
+ throw new IllegalStateException(badBounds(parties, unarrived));
+ else if (par == null) { // directly trip
+ long next = trippedStateFor(onAdvance(phase, parties) ? -1 :
+ ((phase + 1) & phaseMask),
+ parties);
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) {
+ releaseWaiters(phase);
+ break;
}
}
- else if (phase != phaseOf(root.state)) // or if unreconciled
+ else if (phaseOf(root.state) == phase &&
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, s - 1)) {
+ par.arrive(); // cascade to parent
reconcileState();
- else
- throw new IllegalStateException(badBounds(parties, unarrived));
+ break;
+ }
}
return phase;
}
@@ -478,52 +506,48 @@ public class Phaser {
* 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.
+ * from its parent. It is an unenforced usage error for an
+ * unregistered party to invoke this method.
*
* @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
+ // similar to arrive, but too different to merge
Phaser par = parent;
+ long s;
int phase;
- for (;;) {
- long s = state;
- phase = phaseOf(s);
- if (phase < 0)
- break;
+ while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
int parties = partiesOf(s) - 1;
int unarrived = unarrivedOf(s) - 1;
- if (parties >= 0) {
- if (unarrived > 0 || (unarrived == 0 && par != null)) {
- if (casState
- (s,
- stateFor(phase, parties, unarrived))) {
- if (unarrived == 0) {
- par.arriveAndDeregister();
- reconcileState();
- }
- break;
- }
- continue;
- }
- if (unarrived == 0) {
- if (casState
- (s,
- trippedStateFor(onAdvance(phase, parties) ? -1 :
- ((phase + 1) & phaseMask), parties))) {
- releaseWaiters(phase);
- break;
- }
- continue;
+ if (unarrived > 0) {
+ long next = stateFor(phase, parties, unarrived);
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
+ break;
+ }
+ else if (unarrived < 0)
+ throw new IllegalStateException(badBounds(parties, unarrived));
+ else if (par == null) {
+ long next = trippedStateFor(onAdvance(phase, parties)? -1:
+ (phase + 1) & phaseMask,
+ parties);
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) {
+ releaseWaiters(phase);
+ break;
}
- if (par != null && phase != phaseOf(root.state)) {
+ }
+ else if (phaseOf(root.state) == phase) {
+ long next = stateFor(phase, parties, 0);
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) {
+ if (parties == 0)
+ par.arriveAndDeregister();
+ else
+ par.arrive();
reconcileState();
- continue;
+ break;
}
}
- throw new IllegalStateException(badBounds(parties, unarrived));
}
return phase;
}
@@ -532,9 +556,10 @@ public class Phaser {
* Arrives at the barrier 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}.
+ * 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.
*
* @return the arrival phase number, or a negative number if terminated
* @throws IllegalStateException if not terminated and the number
@@ -559,22 +584,18 @@ public class Phaser {
public int awaitAdvance(int phase) {
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
+ int p = getPhase();
if (p != phase)
return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvance(phase);
- // Fall here even if parent waited, to reconcile and help release
return untimedWait(phase);
}
/**
* Awaits the phase of the barrier 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.
+ * 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.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
@@ -587,21 +608,19 @@ public class Phaser {
throws InterruptedException {
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
+ int p = getPhase();
if (p != phase)
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
- * 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.
+ * 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.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
@@ -618,15 +637,13 @@ public class Phaser {
public int awaitAdvanceInterruptibly(int phase,
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
+ int p = getPhase();
if (p != phase)
return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase, timeout, unit);
- return timedWait(phase, unit.toNanos(timeout));
+ return timedWait(phase, nanos);
}
/**
@@ -637,20 +654,15 @@ public class Phaser {
* 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);
- releaseWaiters(1);
- if (parent != null)
- parent.forceTermination();
- return;
- }
- }
+ Phaser r = root; // force at root then reconcile
+ long s;
+ while (phaseOf(s = r.state) >= 0)
+ UNSAFE.compareAndSwapLong(r, stateOffset, s,
+ stateFor(-1, partiesOf(s),
+ unarrivedOf(s)));
+ reconcileState();
+ releaseWaiters(0); // ensure wakeups on both queues
+ releaseWaiters(1);
}
/**
@@ -670,7 +682,7 @@ public class Phaser {
* @return the number of parties
*/
public int getRegisteredParties() {
- return partiesOf(state);
+ return partiesOf(getReconciledState());
}
/**
@@ -680,7 +692,7 @@ public class Phaser {
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(state);
+ return arrivedOf(getReconciledState());
}
/**
@@ -690,7 +702,7 @@ public class Phaser {
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(state);
+ return unarrivedOf(getReconciledState());
}
/**
@@ -722,26 +734,33 @@ public class Phaser {
}
/**
- * Overridable method to perform an action upon phase advance, and
- * to control termination. This method is invoked whenever the
- * barrier is tripped (and thus all other waiting parties are
- * dormant). If it returns {@code true}, then, rather than advance
- * the phase number, this barrier will be set to a final
- * termination state, and subsequent calls to {@link #isTerminated}
- * will return true.
+ * 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
+ * waiting parties are dormant). If this method returns {@code
+ * true}, then, rather than advance the phase number, this barrier
+ * will be set to a final termination state, and subsequent calls
+ * to {@link #isTerminated} will return true. Any (unchecked)
+ * Exception or Error thrown by an invocation of this method is
+ * propagated to the party attempting to trip the barrier, in
+ * which case no advance occurs.
+ *
+ * The arguments to this method provide the state of the phaser
+ * prevailing for the current transition. The results and effects
+ * of invoking phase-related methods (including {@code getPhase}
+ * as well as arrival, registration, and waiting methods) from
+ * within {@code onAdvance} are unspecified and should not be
+ * relied on. Similarly, while it is possible to override this
+ * method to produce side-effects visible to participating tasks,
+ * it is in general safe to do so only in designs in which all
+ * parties register before any arrive, and all {@link
+ * #awaitAdvance} at each phase.
*
*
The default version returns {@code true} when the number of
* registered parties is zero. Normally, overrides that arrange
* termination for other reasons should also preserve this
* property.
*
- *
You may override this method to perform an action with side
- * effects visible to participating tasks, but it is in general
- * only sensible to do so in designs where all parties register
- * before any arrive, and all {@link #awaitAdvance} at each phase.
- * Otherwise, you cannot ensure lack of interference from other
- * parties during the invocation of this method.
- *
* @param phase the phase number on entering the barrier
* @param registeredParties the current number of registered parties
* @return {@code true} if this barrier should terminate
@@ -782,6 +801,7 @@ public class Phaser {
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;
@@ -792,12 +812,14 @@ public class Phaser {
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;
@@ -814,6 +836,7 @@ public class Phaser {
}
return isReleasable();
}
+
void signal() {
Thread t = thread;
if (t != null) {
@@ -821,16 +844,17 @@ public class Phaser {
LockSupport.unpark(t);
}
}
+
boolean doWait() {
if (thread != null) {
try {
- ForkJoinPool.managedBlock(this, false);
+ ForkJoinPool.managedBlock(this);
} catch (InterruptedException ie) {
+ wasInterrupted = true; // can't currently happen
}
}
return wasInterrupted;
}
-
}
/**
@@ -856,6 +880,12 @@ public class Phaser {
}
/**
+ * The number of times to spin before blocking waiting for advance.
+ */
+ static final int MAX_SPINS =
+ Runtime.getRuntime().availableProcessors() == 1 ? 0 : 1 << 8;
+
+ /**
* Enqueues node and waits unless aborted or signalled.
*
* @return current phase
@@ -864,16 +894,21 @@ public class Phaser {
QNode node = null;
boolean queued = false;
boolean interrupted = false;
+ int spins = MAX_SPINS;
int p;
while ((p = getPhase()) == phase) {
if (Thread.interrupted())
interrupted = true;
+ else if (spins > 0) {
+ if (--spins == 0)
+ Thread.yield();
+ }
else if (node == null)
node = new QNode(this, phase, false, false, 0, 0);
else if (!queued)
queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
+ else if (node.doWait())
+ interrupted = true;
}
if (node != null)
node.thread = null;
@@ -891,16 +926,21 @@ public class Phaser {
QNode node = null;
boolean queued = false;
boolean interrupted = false;
+ int spins = MAX_SPINS;
int p;
while ((p = getPhase()) == phase && !interrupted) {
if (Thread.interrupted())
interrupted = true;
+ else if (spins > 0) {
+ if (--spins == 0)
+ Thread.yield();
+ }
else if (node == null)
node = new QNode(this, phase, true, false, 0, 0);
else if (!queued)
queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
+ else if (node.doWait())
+ interrupted = true;
}
if (node != null)
node.thread = null;
@@ -921,18 +961,23 @@ public class Phaser {
QNode node = null;
boolean queued = false;
boolean interrupted = false;
+ int spins = MAX_SPINS;
int p;
while ((p = getPhase()) == phase && !interrupted) {
if (Thread.interrupted())
interrupted = true;
else if (nanos - (System.nanoTime() - startTime) <= 0)
break;
+ else if (spins > 0) {
+ if (--spins == 0)
+ Thread.yield();
+ }
else if (node == null)
node = new QNode(this, phase, true, true, startTime, nanos);
else if (!queued)
queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
+ else if (node.doWait())
+ interrupted = true;
}
if (node != null)
node.thread = null;
@@ -951,10 +996,6 @@ public class Phaser {
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));