--- jsr166/src/jsr166y/Phaser.java 2010/12/03 21:29:34 1.67
+++ jsr166/src/jsr166y/Phaser.java 2010/12/04 15:25:08 1.68
@@ -75,18 +75,19 @@ import java.util.concurrent.locks.LockSu
*
*
* Termination. A 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}. 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.
+ * state, that may be checked using method {@link #isTerminated}. Upon
+ * termination, all synchronization methods immediately return without
+ * waiting for advance, as indicated by a negative return
+ * value. Similarly, attempts to register upon termination have no
+ * effect. Termination is triggered when an invocation of {@code
+ * onAdvance} returns {@code true}. The default implementation returns
+ * {@code true} if a deregistration has caused the number of
+ * registered parties to become zero. As illustrated below, when
+ * phasers control actions with a fixed number of iterations, it is
+ * often convenient to override this method to cause termination when
+ * the current phase number reaches a threshold. Method {@link
+ * #forceTermination} is also available to abruptly release waiting
+ * threads and allow them to terminate.
*
*
Tiering. Phasers may be tiered (i.e.,
* constructed in tree structures) to reduce contention. Phasers with
@@ -96,6 +97,16 @@ import java.util.concurrent.locks.LockSu
* increase throughput even though it incurs greater per-operation
* overhead.
*
+ *
In a tree of tiered phasers, registration and deregistration of
+ * child phasers with their parent are managed automatically.
+ * Whenever the number of registered parties of a child phaser becomes
+ * non-zero (as established in the {@link #Phaser(Phaser,int)}
+ * constructor, {@link #register}, or {@link #bulkRegister}), the
+ * child phaser is registered with its parent. Whenever the number of
+ * registered parties becomes zero as the result of an invocation of
+ * {@link #arriveAndDeregister}, the child phaser is deregistered
+ * from its parent.
+ *
*
Monitoring. While synchronization methods may be invoked
* only by registered parties, the current state of a phaser may be
* monitored by any caller. At any given moment there are {@link
@@ -277,8 +288,7 @@ public class Phaser {
}
private static int partiesOf(long s) {
- int counts = (int)s;
- return (counts == EMPTY) ? 0 : counts >>> PARTIES_SHIFT;
+ return (int)s >>> PARTIES_SHIFT;
}
private static int phaseOf(long s) {
@@ -339,41 +349,37 @@ public class Phaser {
*/
private int doArrive(boolean deregister) {
int adj = deregister ? ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL;
- long s;
- int phase;
- while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0) {
+ final Phaser root = this.root;
+ for (;;) {
+ long s = (root == this) ? state : reconcileState();
+ int phase = (int)(s >>> PHASE_SHIFT);
int counts = (int)s;
- int unarrived = counts & UNARRIVED_MASK;
- if (counts == EMPTY || unarrived == 0) {
- if (reconcileState() == s)
+ int unarrived = (counts & UNARRIVED_MASK) - 1;
+ if (phase < 0)
+ return phase;
+ else if (counts == EMPTY || unarrived < 0) {
+ if (root == this || reconcileState() == s)
throw new IllegalStateException(badArrive(s));
}
else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
- if (unarrived == 1) {
- long n = s & PARTIES_MASK; // unshifted parties field
- int u = ((int)n) >>> PARTIES_SHIFT;
- Phaser par = parent;
- if (par != null) {
- par.doArrive(u == 0);
- reconcileState();
- }
- else {
- n |= (((long)((phase+1) & MAX_PHASE)) << PHASE_SHIFT);
- if (onAdvance(phase, u))
- n |= TERMINATION_BIT;
- else if (u == 0)
- n |= EMPTY; // reset to unregistered
- else
- n |= (long)u; // reset unarr to parties
- // assert state == s || isTerminated();
- UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
- releaseWaiters(phase);
- }
+ if (unarrived == 0) {
+ long n = s & PARTIES_MASK; // base of next state
+ int nextUnarrived = ((int)n) >>> PARTIES_SHIFT;
+ if (root != this)
+ return parent.doArrive(nextUnarrived == 0);
+ if (onAdvance(phase, nextUnarrived))
+ n |= TERMINATION_BIT;
+ else if (nextUnarrived == 0)
+ n |= EMPTY;
+ else
+ n |= nextUnarrived;
+ n |= ((long)((phase + 1) & MAX_PHASE)) << PHASE_SHIFT;
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
+ releaseWaiters(phase);
}
- break;
+ return phase;
}
}
- return phase;
}
/**
@@ -490,15 +496,9 @@ public class 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.
+ * registered unarrived parties. When the given parent is non-null
+ * and the given number of parties is greater than zero, this
+ * child phaser is registered with its parent.
*
* @param parent the parent phaser
* @param parties the number of parties required to advance to the
@@ -512,10 +512,10 @@ public class Phaser {
int phase = 0;
this.parent = parent;
if (parent != null) {
- Phaser r = parent.root;
- this.root = r;
- this.evenQ = r.evenQ;
- this.oddQ = r.oddQ;
+ final Phaser root = parent.root;
+ this.root = root;
+ this.evenQ = root.evenQ;
+ this.oddQ = root.oddQ;
if (parties != 0)
phase = parent.doRegister(1);
}
@@ -524,7 +524,7 @@ public class Phaser {
this.evenQ = new AtomicReference();
this.oddQ = new AtomicReference();
}
- this.state = (parties == 0) ? ((long) EMPTY) :
+ this.state = (parties == 0) ? (long) EMPTY :
((((long) phase) << PHASE_SHIFT) |
(((long) parties) << PARTIES_SHIFT) |
((long) parties));
@@ -535,9 +535,13 @@ public class Phaser {
* 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
+ * this child phaser is also registered with its parent. If
+ * this phaser is terminated, the attempt to register has
+ * no effect, and a negative value is returned.
+ *
+ * @return the arrival phase number to which this registration
+ * applied. If this value is negative, then this phaser has
+ * terminated, in which casem registration has no effect.
* @throws IllegalStateException if attempting to register more
* than the maximum supported number of parties
*/
@@ -549,13 +553,17 @@ 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 await its completion before returning. If this
- * phaser has a parent, and the given number of parties is
- * greater than zero, and this phaser previously had no registered
- * parties, this phaser is also registered with its parent.
+ * phaser has a parent, and the given number of parties is greater
+ * than zero, and this phaser previously had no registered
+ * parties, this child phaser is also registered with its parent.
+ * If this phaser is terminated, the attempt to register has no
+ * effect, and a negative value is returned.
*
* @param parties the number of additional parties required to
* advance to the next phase
- * @return the arrival phase number to which this registration applied
+ * @return the arrival phase number to which this registration
+ * applied. If this value is negative, then this phaser has
+ * terminated, in which casem registration has no effect.
* @throws IllegalStateException if attempting to register more
* than the maximum supported number of parties
* @throws IllegalArgumentException if {@code parties < 0}
@@ -617,12 +625,47 @@ public class Phaser {
* IllegalStateException} only upon some subsequent operation on
* this phaser, if ever.
*
- * @return the arrival phase number, or a negative number if terminated
+ * @return the arrival phase number, or the (negative)
+ * {@linkplain #getPhase() current phase} if terminated
* @throws IllegalStateException if not terminated and the number
* of unarrived parties would become negative
*/
public int arriveAndAwaitAdvance() {
- return awaitAdvance(doArrive(false));
+ // Specialization of doArrive+awaitAdvance eliminating some reads/paths
+ final Phaser root = this.root;
+ for (;;) {
+ long s = (root == this) ? state : reconcileState();
+ int phase = (int)(s >>> PHASE_SHIFT);
+ int counts = (int)s;
+ int unarrived = (counts & UNARRIVED_MASK) - 1;
+ if (phase < 0)
+ return phase;
+ else if (counts == EMPTY || unarrived < 0) {
+ if (reconcileState() == s)
+ throw new IllegalStateException(badArrive(s));
+ }
+ else if (UNSAFE.compareAndSwapLong(this, stateOffset, s,
+ s -= ONE_ARRIVAL)) {
+ if (unarrived != 0)
+ return root.internalAwaitAdvance(phase, null);
+ if (root != this)
+ return parent.arriveAndAwaitAdvance();
+ long n = s & PARTIES_MASK; // base of next state
+ int nextUnarrived = ((int)n) >>> PARTIES_SHIFT;
+ if (onAdvance(phase, nextUnarrived))
+ n |= TERMINATION_BIT;
+ else if (nextUnarrived == 0)
+ n |= EMPTY;
+ else
+ n |= nextUnarrived;
+ int nextPhase = (phase + 1) & MAX_PHASE;
+ n |= (long)nextPhase << PHASE_SHIFT;
+ if (!UNSAFE.compareAndSwapLong(this, stateOffset, s, n))
+ return (int)(state >>> PHASE_SHIFT); // terminated
+ releaseWaiters(phase);
+ return nextPhase;
+ }
+ }
}
/**
@@ -633,19 +676,17 @@ public class Phaser {
* @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 {@code arriveAndDeregister}.
- * @return the next arrival phase number, or a negative value
- * if terminated or argument is negative
+ * @return the next arrival phase number, or the argument if it is
+ * negative, or the (negative) {@linkplain #getPhase() current phase}
+ * if terminated
*/
public int awaitAdvance(int phase) {
- Phaser rt;
- int p = (int)(state >>> PHASE_SHIFT);
+ final Phaser root = this.root;
+ int p = (int)((root == this? state : reconcileState()) >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- if (p == phase) {
- if ((p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
- return rt.internalAwaitAdvance(phase, null);
- reconcileState();
- }
+ if (p == phase)
+ return root.internalAwaitAdvance(phase, null);
return p;
}
@@ -659,25 +700,22 @@ public class Phaser {
* @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 {@code arriveAndDeregister}.
- * @return the next arrival phase number, or a negative value
- * if terminated or argument is negative
+ * @return the next arrival phase number, or the argument if it is
+ * negative, or the (negative) {@linkplain #getPhase() current phase}
+ * if terminated
* @throws InterruptedException if thread interrupted while waiting
*/
public int awaitAdvanceInterruptibly(int phase)
throws InterruptedException {
- Phaser rt;
- int p = (int)(state >>> PHASE_SHIFT);
+ final Phaser root = this.root;
+ int p = (int)((root == this? state : reconcileState()) >>> PHASE_SHIFT);
if (phase < 0)
return phase;
if (p == phase) {
- if ((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();
- }
- else
- reconcileState();
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = root.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
}
return p;
}
@@ -696,8 +734,9 @@ public class Phaser {
* {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the
* {@code timeout} parameter
- * @return the next arrival phase number, or a negative value
- * if terminated or argument is negative
+ * @return the next arrival phase number, or the argument if it is
+ * negative, or the (negative) {@linkplain #getPhase() current phase}
+ * if terminated
* @throws InterruptedException if thread interrupted while waiting
* @throws TimeoutException if timed out while waiting
*/
@@ -705,21 +744,17 @@ public class Phaser {
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
long nanos = unit.toNanos(timeout);
- Phaser rt;
- int p = (int)(state >>> PHASE_SHIFT);
+ final Phaser root = this.root;
+ int p = (int)((root == this? state : reconcileState()) >>> PHASE_SHIFT);
if (phase < 0)
return phase;
if (p == phase) {
- if ((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();
- }
- else
- reconcileState();
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = root.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else if (p == phase)
+ throw new TimeoutException();
}
return p;
}
@@ -738,9 +773,10 @@ public class Phaser {
final Phaser root = this.root;
long s;
while ((s = root.state) >= 0) {
- long next = (s & ~(long)(MAX_PARTIES)) | TERMINATION_BIT;
+ long next = (s & ~((long)UNARRIVED_MASK)) | TERMINATION_BIT;
if (UNSAFE.compareAndSwapLong(root, stateOffset, s, next)) {
- releaseWaiters(0); // signal all threads
+ // signal all threads
+ releaseWaiters(0);
releaseWaiters(1);
return;
}
@@ -891,9 +927,7 @@ public class Phaser {
*/
private void releaseWaiters(int phase) {
QNode q; // first element of queue
- int p; // its phase
Thread t; // its thread
- // assert phase != phaseOf(root.state);
AtomicReference head = (phase & 1) == 0 ? evenQ : oddQ;
while ((q = head.get()) != null &&
q.phase != (int)(root.state >>> PHASE_SHIFT)) {
@@ -905,6 +939,30 @@ public class Phaser {
}
}
+ /**
+ * Variant of releaseWaiters that additionally tries to remove any
+ * nodes no longer waiting for advance due to timeout or
+ * interrupt. Currently, nodes are removed only if they are at
+ * head of queue, which suffices to reduce memory footprint in
+ * most usages.
+ *
+ * @return current phase on exit
+ */
+ private int abortWait(int phase) {
+ AtomicReference head = (phase & 1) == 0 ? evenQ : oddQ;
+ for (;;) {
+ Thread t;
+ QNode q = head.get();
+ int p = (int)(root.state >>> PHASE_SHIFT);
+ if (q == null || ((t = q.thread) != null && q.phase == p))
+ return p;
+ if (head.compareAndSet(q, q.next) && t != null) {
+ q.thread = null;
+ LockSupport.unpark(t);
+ }
+ }
+ }
+
/** The number of CPUs, for spin control */
private static final int NCPU = Runtime.getRuntime().availableProcessors();
@@ -973,7 +1031,7 @@ public class Phaser {
if (node.wasInterrupted && !node.interruptible)
Thread.currentThread().interrupt();
if (p == phase && (p = (int)(state >>> PHASE_SHIFT)) == phase)
- return p; // recheck abort
+ return abortWait(phase); // possibly clean up on abort
}
releaseWaiters(phase);
return p;