--- jsr166/src/jsr166y/Phaser.java 2008/10/28 23:03:24 1.6 +++ jsr166/src/jsr166y/Phaser.java 2009/03/19 05:10:42 1.12 @@ -5,6 +5,7 @@ */ package jsr166y; + import java.util.concurrent.*; import java.util.concurrent.atomic.*; import java.util.concurrent.locks.LockSupport; @@ -13,9 +14,9 @@ import java.lang.reflect.*; /** * A reusable synchronization barrier, similar in functionality to a - * {@link java.util.concurrent.CyclicBarrier} and {@link - * java.util.concurrent.CountDownLatch} but supporting more flexible - * usage. + * {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and + * {@link java.util.concurrent.CountDownLatch CountDownLatch} + * but supporting more flexible usage. * *
Sample usages: * - *
A Phaser may be used instead of a CountdownLatch to control + *
A 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: @@ -108,12 +112,12 @@ import java.lang.reflect.*; * int p = phaser.arriveAndDeregister(); // deregister self ... * p = phaser.awaitAdvance(p); // ... and await arrival * otherActions(); // do other things while tasks execute - * phaser.awaitAdvance(p); // awit final completion + * phaser.awaitAdvance(p); // await final completion * } * * *
One way to cause a set of threads to repeatedly perform actions - * for a given number of iterations is to override onAdvance: + * for a given number of iterations is to override {@code onAdvance}: * *
* void startTasks(List<Runnable> list, final int iterations) { @@ -163,7 +167,7 @@ import java.lang.reflect.*; * build(new Task[n], 0, n, new Phaser()); ** - * The best value of TASKS_PER_PHASER depends mainly on + * 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 * high rates), or up to hundreds for extremely large ones. @@ -195,24 +199,24 @@ public class Phaser { * 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 performace relies on keeping state decoding + * 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 - * being lowest 16 bits. + * count being lowest 16 bits. */ private volatile long state; private static final int ushortBits = 16; - private static final int ushortMask = (1 << ushortBits) - 1; - private static final int phaseMask = 0x7fffffff; + private static final int ushortMask = 0xffff; + private static final int phaseMask = 0x7fffffff; private static int unarrivedOf(long s) { return (int)(s & ushortMask); } private static int partiesOf(long s) { - return (int)(s & (ushortMask << 16)) >>> 16; + return ((int)s) >>> 16; } private static int phaseOf(long s) { @@ -224,17 +228,21 @@ public class Phaser { } private static long stateFor(int phase, int parties, int unarrived) { - return (((long)phase) << 32) | ((parties << 16) | unarrived); + return ((((long)phase) << 32) | (((long)parties) << 16) | + (long)unarrived); } private static long trippedStateFor(int phase, int parties) { - return (((long)phase) << 32) | ((parties << 16) | parties); + long lp = (long)parties; + return (((long)phase) << 32) | (lp << 16) | lp; } - private static IllegalStateException badBounds(int parties, int unarrived) { - return new IllegalStateException - ("Attempt to set " + unarrived + - " unarrived of " + parties + " parties"); + /** + * Returns message string for bad bounds exceptions + */ + private static String badBounds(int parties, int unarrived) { + return ("Attempt to set " + unarrived + + " unarrived of " + parties + " parties"); } /** @@ -251,7 +259,7 @@ public class Phaser { // Wait queues /** - * Heads of Treiber stacks waiting for nonFJ threads. To eliminate + * Heads of Treiber stacks for waiting threads. To eliminate * contention while releasing some threads while adding others, we * use two of them, alternating across even and odd phases. */ @@ -295,7 +303,8 @@ public class Phaser { /** * Creates a new Phaser without any initially registered parties, - * initial phase number 0, and no parent. + * initial phase number 0, and no parent. Any thread using this + * Phaser will need to first register for it. */ public Phaser() { this(null); @@ -393,7 +402,7 @@ public class Phaser { if (phase < 0) break; if (parties > ushortMask || unarrived > ushortMask) - throw badBounds(parties, unarrived); + throw new IllegalStateException(badBounds(parties, unarrived)); if (phase == phaseOf(root.state) && casState(s, stateFor(phase, parties, unarrived))) break; @@ -415,6 +424,8 @@ public class Phaser { 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 @@ -440,12 +451,10 @@ public class Phaser { } } } - else if (phase < 0) // Don't throw exception if terminated - break; else if (phase != phaseOf(root.state)) // or if unreconciled reconcileState(); else - throw badBounds(parties, unarrived); + throw new IllegalStateException(badBounds(parties, unarrived)); } return phase; } @@ -469,6 +478,8 @@ public class Phaser { for (;;) { long s = state; phase = phaseOf(s); + if (phase < 0) + break; int parties = partiesOf(s) - 1; int unarrived = unarrivedOf(s) - 1; if (parties >= 0) { @@ -494,21 +505,19 @@ public class Phaser { } continue; } - if (phase < 0) - break; if (par != null && phase != phaseOf(root.state)) { reconcileState(); continue; } } - throw badBounds(parties, unarrived); + throw new IllegalStateException(badBounds(parties, unarrived)); } return phase; } /** * Arrives at the barrier and awaits others. Equivalent in effect - * to awaitAdvance(arrive()). If you instead need to + * to {@code awaitAdvance(arrive())}. If you instead need to * await with interruption of timeout, and/or deregister upon * arrival, you can arrange them using analogous constructions. * @return the phase on entry to this method @@ -533,7 +542,7 @@ public class Phaser { int p = phaseOf(s); if (p != phase) return p; - if (unarrivedOf(s) == 0) + if (unarrivedOf(s) == 0 && parent != null) parent.awaitAdvance(phase); // Fall here even if parent waited, to reconcile and help release return untimedWait(phase); @@ -541,21 +550,22 @@ public class Phaser { /** * Awaits the phase of the barrier to advance from the given - * value, or returns immediately if argumet is negative or this + * value, or returns immediately if argument is negative or this * barrier is terminated, or throws InterruptedException if * interrupted while waiting. * @param phase the phase on entry to this method * @return the phase on exit from this method * @throws InterruptedException if thread interrupted while waiting */ - public int awaitAdvanceInterruptibly(int phase) throws InterruptedException { + public int awaitAdvanceInterruptibly(int phase) + throws InterruptedException { if (phase < 0) return phase; long s = getReconciledState(); int p = phaseOf(s); if (p != phase) return p; - if (unarrivedOf(s) != 0) + if (unarrivedOf(s) == 0 && parent != null) parent.awaitAdvanceInterruptibly(phase); return interruptibleWait(phase); } @@ -577,7 +587,7 @@ public class Phaser { int p = phaseOf(s); if (p != phase) return p; - if (unarrivedOf(s) == 0) + if (unarrivedOf(s) == 0 && parent != null) parent.awaitAdvanceInterruptibly(phase, timeout, unit); return timedWait(phase, unit.toNanos(timeout)); } @@ -608,7 +618,7 @@ public class Phaser { /** * Returns the current phase number. The maximum phase number is - * Integer.MAX_VALUE, after which it restarts at + * {@code Integer.MAX_VALUE}, after which it restarts at * zero. Upon termination, the phase number is negative. * @return the phase number, or a negative value if terminated */ @@ -617,9 +627,9 @@ public class Phaser { } /** - * Returns true if the current phase number equals the given phase. + * Returns {@code true} if the current phase number equals the given phase. * @param phase the phase - * @return true if the current phase number equals the given phase. + * @return {@code true} if the current phase number equals the given phase */ public final boolean hasPhase(int phase) { return phaseOf(getReconciledState()) == phase; @@ -653,7 +663,7 @@ public class Phaser { /** * Returns the parent of this phaser, or null if none. - * @return the parent of this phaser, or null if none. + * @return the parent of this phaser, or null if none */ public Phaser getParent() { return parent; @@ -662,15 +672,15 @@ public class Phaser { /** * 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; } /** - * Returns true if this barrier has been terminated. - * @return true if this barrier has been terminated + * Returns {@code true} if this barrier has been terminated. + * @return {@code true} if this barrier has been terminated */ public boolean isTerminated() { return getPhase() < 0; @@ -682,7 +692,7 @@ public class Phaser { * barrier is tripped (and thus all other waiting parties are * dormant). If it returns true, then, rather than advance the * phase number, this barrier will be set to a final termination - * state, and subsequent calls to isTerminated will + * state, and subsequent calls to {@code isTerminated} will * return true. * *
The default version returns true when the number of @@ -693,7 +703,7 @@ public class Phaser { *
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 awaitAdvance at each phase.
+ * before any arrive, and all {@code awaitAdvance} at each phase.
* Otherwise, you cannot ensure lack of interference. In
* particular, this method may be invoked more than once per
* transition if other parties successfully register while the
@@ -702,9 +712,8 @@ public class Phaser {
* method.
*
* @param phase the phase number on entering the barrier
- * @param registeredParties the current number of registered
- * parties.
- * @return true if this barrier should terminate
+ * @param registeredParties the current number of registered parties
+ * @return {@code true} if this barrier should terminate
*/
protected boolean onAdvance(int phase, int registeredParties) {
return registeredParties <= 0;
@@ -713,51 +722,67 @@ public class Phaser {
/**
* 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 ="}
+ * "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
+ * "arrived = "} followed by the number of arrived parties.
*
* @return a string identifying this barrier, as well as its state
*/
public String toString() {
long s = getReconciledState();
- return super.toString() + "[phase = " + phaseOf(s) + " parties = " + partiesOf(s) + " arrived = " + arrivedOf(s) + "]";
+ return super.toString() +
+ "[phase = " + phaseOf(s) +
+ " parties = " + partiesOf(s) +
+ " arrived = " + arrivedOf(s) + "]";
}
// methods for waiting
- /** The number of CPUs, for spin control */
- static final int NCPUS = Runtime.getRuntime().availableProcessors();
-
- /**
- * The number of times to spin before blocking in timed waits.
- * The value is empirically derived.
- */
- static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
-
- /**
- * The number of times to spin before blocking in untimed waits.
- * This is greater than timed value because untimed waits spin
- * faster since they don't need to check times on each spin.
- */
- static final int maxUntimedSpins = maxTimedSpins * 32;
-
/**
- * The number of nanoseconds for which it is faster to spin
- * rather than to use timed park. A rough estimate suffices.
+ * Wait nodes for Treiber stack representing wait queue
*/
- static final long spinForTimeoutThreshold = 1000L;
-
- /**
- * Wait nodes for Treiber stack representing wait queue for non-FJ
- * tasks.
- */
- static final class QNode {
- QNode next;
+ 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() {
+ 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) {
@@ -765,6 +790,16 @@ public class Phaser {
LockSupport.unpark(t);
}
}
+ boolean doWait() {
+ if (thread != null) {
+ try {
+ ForkJoinPool.managedBlock(this, false);
+ } catch (InterruptedException ie) {
+ }
+ }
+ return wasInterrupted;
+ }
+
}
/**
@@ -780,132 +815,141 @@ public class Phaser {
}
/**
+ * Tries to enqueue given node in the appropriate wait queue
+ * @return true if successful
+ */
+ private boolean tryEnqueue(QNode node) {
+ AtomicReference