--- jsr166/src/jsr166y/Phaser.java 2008/07/25 18:10:41 1.2
+++ jsr166/src/jsr166y/Phaser.java 2010/11/27 16:46:53 1.59
@@ -5,691 +5,1058 @@
*/
package jsr166y;
-import jsr166y.forkjoin.*;
-import java.util.concurrent.*;
-import java.util.concurrent.atomic.*;
+
+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 a
- * {@link java.util.concurrent.CyclicBarrier}, but supporting more
- * flexible usage.
+ * A reusable synchronization barrier, similar in functionality to
+ * {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and
+ * {@link java.util.concurrent.CountDownLatch CountDownLatch}
+ * but supporting more flexible usage.
*
- *
+ * 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.)
*
- *
- The number of parties synchronizing on the barrier may vary
- * over time. A task may register to be a party in a barrier at any
- * time, and may deregister upon arriving at the barrier. 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.
- *
- *
- Each generation has an associated phase value, starting at
- * zero, and advancing when all parties reach the barrier (wrapping
- * around to zero after reaching Integer.MAX_VALUE).
- *
- *
- Like a CyclicBarrier, a Phaser may be repeatedly awaited.
- * Method arriveAndAwaitAdvance has effect analogous to
- * CyclicBarrier.await. However, Phasers separate two
- * aspects of coordination, that may be invoked independently:
+ *
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:
*
*
*
- * - Arriving at a barrier. Methods arrive and
- * arriveAndDeregister do not block, but return
- * the phase value on entry to the method.
- *
- *
- Awaiting others. Method awaitAdvance requires an
- * argument indicating the entry phase, and returns when the
- * barrier advances to a new phase.
+ *
- Arrival. Methods {@link #arrive} and
+ * {@link #arriveAndDeregister} record arrival at a
+ * barrier. These methods do not block, but return an associated
+ * arrival phase number; 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}.
+ *
+ *
- Waiting. 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.
+ * 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
+ * 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.
+ *
*
*
+ * 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}. 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.
*
- *
- Barrier actions, performed by the task triggering a phase
- * advance while others may be waiting, are arranged by overriding
- * method onAdvance, that also controls termination.
- *
- *
- Phasers may enter a termination state in which all
- * await actions immediately return, indicating (via a negative phase
- * value) that execution is complete. Termination is triggered by
- * executing the overridable onAdvance method that is invoked
- * each time the barrier is tripped. When a Phaser is controlling an
- * action 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 forceTermination is
- * also available to assist recovery actions upon failure.
- *
- *
- Unlike most synchronizers, a Phaser may also be used with
- * ForkJoinTasks (as well as plain threads).
- *
- *
- By default, awaitAdvance continues to wait even if
- * the current thread is interrupted. And unlike the case in
- * CyclicBarriers, exceptions encountered while tasks wait
- * interruptibly or with timeout do not change the state of the
- * barrier. If necessary, you can perform any associated recovery
- * within handlers of those exceptions.
+ *
Tiering. Phasers may be tiered (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.
*
- *
+ * 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})
+ * 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:
+ *
+ *
{@code
+ * void runTasks(List tasks) {
+ * final Phaser phaser = new Phaser(1); // "1" to register self
+ * // create and start threads
+ * for (Runnable task : tasks) {
+ * phaser.register();
+ * new Thread() {
+ * public void run() {
+ * phaser.arriveAndAwaitAdvance(); // await all creation
+ * task.run();
+ * }
+ * }.start();
+ * }
+ *
+ * // allow threads to start and deregister self
+ * phaser.arriveAndDeregister();
+ * }}
+ *
+ * One way to cause a set of threads to repeatedly perform actions
+ * for a given number of iterations is to override {@code onAdvance}:
+ *
+ *
{@code
+ * void startTasks(List tasks, final int iterations) {
+ * final Phaser phaser = new Phaser() {
+ * protected boolean onAdvance(int phase, int registeredParties) {
+ * return phase >= iterations || registeredParties == 0;
+ * }
+ * };
+ * phaser.register();
+ * for (final Runnable task : tasks) {
+ * phaser.register();
+ * new Thread() {
+ * public void run() {
+ * do {
+ * task.run();
+ * phaser.arriveAndAwaitAdvance();
+ * } while (!phaser.isTerminated());
+ * }
+ * }.start();
+ * }
+ * phaser.arriveAndDeregister(); // deregister self, don't wait
+ * }}
*
- * Sample usage:
+ * 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();}
*
- * [todo: non-FJ example]
+ *
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:
*
- *
A Phaser may be used to support a style of programming in
- * which a task waits for others to complete, without otherwise
- * needing to keep track of which tasks it is waiting for. This is
- * similar to the "sync" construct in Cilk and "clocks" in X10.
- * Special constructions based on such barriers are available using
- * the LinkedAsyncAction and CyclicAction classes,
- * but they can be useful in other contexts as well. For a simple
- * (but not very useful) example, here is a variant of Fibonacci:
- *
- *
- * class BarrierFibonacci extends RecursiveAction {
- * int argument, result;
- * final Phaser parentBarrier;
- * BarrierFibonacci(int n, Phaser parentBarrier) {
- * this.argument = n;
- * this.parentBarrier = parentBarrier;
- * parentBarrier.register();
+ * {@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();
* }
- * protected void compute() {
- * int n = argument;
- * if (n <= 1)
- * result = n;
- * else {
- * Phaser childBarrier = new Phaser(1);
- * BarrierFibonacci f1 = new BarrierFibonacci(n - 1, childBarrier);
- * BarrierFibonacci f2 = new BarrierFibonacci(n - 2, childBarrier);
- * f1.fork();
- * f2.fork();
- * childBarrier.arriveAndAwait();
- * result = f1.result + f2.result;
+ * 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 with upon construction:
+ *
+ *
{@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) {
+ * int j = Math.min(i + TASKS_PER_PHASER, hi);
+ * build(actions, i, j, new Phaser(ph));
* }
- * parentBarrier.arriveAndDeregister();
+ * } else {
+ * for (int i = lo; i < hi; ++i)
+ * actions[i] = new Task(ph);
+ * // assumes new Task(ph) performs ph.register()
* }
* }
- *
+ * // .. initially called, for n tasks via
+ * build(new Task[n], 0, n, new Phaser());}
+ *
+ * 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.
*
* Implementation notes: This implementation restricts the
- * maximum number of parties to 65535. Attempts to register
- * additional parties result in IllegalStateExceptions.
+ * 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.
+ *
+ * @since 1.7
+ * @author Doug Lea
*/
public class Phaser {
/*
* This class implements an extension of X10 "clocks". Thanks to
- * Vijay Saraswat for the idea of applying it to ForkJoinTasks,
- * and to Vivek Sarkar for enhancements to extend functionality.
+ * Vijay Saraswat for the idea, and to Vivek Sarkar for
+ * enhancements to extend functionality.
*/
/**
* Barrier state representation. Conceptually, a barrier contains
* four values:
- *
- * * 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 AtomicLong. Termination uses the sign bit
- * of 32 bit representation of phase, so phase is set to -1 on
- * termination.
- */
- private final AtomicLong state;
+ * 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.
+ */
+ private volatile long state;
+
+ private static final int MAX_PARTIES = 0xffff;
+ private static final int MAX_PHASE = 0x7fffffff;
+ private static final int PARTIES_SHIFT = 16;
+ private static final int PHASE_SHIFT = 32;
+ private static final int UNARRIVED_MASK = 0xffff; // 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;
- /**
- * Head of Treiber stack for waiting nonFJ threads.
- */
- private final AtomicReference head = new AtomicReference();
-
- private static final int ushortBits = 16;
- private static final int ushortMask = (1 << ushortBits) - 1;
- private static final int phaseMask = 0x7fffffff;
+ // 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 & (ushortMask << 16)) >>> 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) | ((parties << 16) | unarrived);
- }
+ /**
+ * The parent of this phaser, or null if none
+ */
+ private final Phaser parent;
- private static IllegalStateException badBounds(int parties, int unarrived) {
- return new IllegalStateException("Attempt to set " + unarrived +
- " unarrived of " + parties + " parties");
- }
+ /**
+ * The root of phaser tree. Equals this if not in a tree. Used to
+ * support faster state push-down.
+ */
+ private final Phaser root;
/**
- * Creates a new Phaser without any initially registered parties,
- * and initial phase number 0.
+ * Heads of Treiber stacks for waiting threads. To eliminate
+ * 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.
*/
- public Phaser() {
- state = new AtomicLong(stateFor(0, 0, 0));
+ private final AtomicReference evenQ;
+ private final AtomicReference oddQ;
+
+ private AtomicReference queueFor(int phase) {
+ return ((phase & 1) == 0) ? evenQ : oddQ;
}
/**
- * Creates a new Phaser with the given numbers of registered
- * unarrived parties and initial phase number 0.
- * @param parties the number of parties required to trip barrier.
- * @throws IllegalArgumentException if parties less than zero
- * or greater than the maximum number of parties supported.
+ * Returns message string for bounds exceptions on arrival.
*/
- public Phaser(int parties) {
- if (parties < 0 || parties > ushortMask)
- throw new IllegalArgumentException("Illegal number of parties");
- state = new AtomicLong(stateFor(0, parties, parties));
+ private String badArrive(long s) {
+ return "Attempted arrival of unregistered party for " +
+ stateToString(s);
}
/**
- * Adds a new unarrived party to this phaser.
- * @return the current barrier phase number upon registration
- * @throws IllegalStateException if attempting to register more
- * than the maximum supported number of parties.
+ * Returns message string for bounds exceptions on registration.
*/
- public int register() { // increment both parties and unarrived
- final AtomicLong state = this.state;
- for (;;) {
- long s = state.get();
- int phase = phaseOf(s);
- int parties = partiesOf(s) + 1;
- int unarrived = unarrivedOf(s) + 1;
- if (parties > ushortMask || unarrived > ushortMask)
- throw badBounds(parties, unarrived);
- if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
- return phase;
- }
+ private String badRegister(long s) {
+ return "Attempt to register more than " +
+ MAX_PARTIES + " parties for " + stateToString(s);
}
/**
- * Arrives at the barrier, but does not wait for others. (You can
- * in turn wait for others via {@link #awaitAdvance}).
+ * 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.
*
- * @return the current barrier phase number upon entry to
- * this method, or a negative value if terminated;
- * @throws IllegalStateException if the number of unarrived
- * parties would become negative.
+ * @param adj - adjustment to apply to state -- either
+ * ONE_ARRIVAL (for arrive) or
+ * ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
*/
- public int arrive() { // decrement unarrived. If zero, trip
- final AtomicLong state = this.state;
+ private int doArrive(long adj) {
for (;;) {
- long s = state.get();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s) - 1;
- if (unarrived < 0)
- throw badBounds(parties, unarrived);
- if (unarrived == 0 && phase >= 0) {
- trip(phase, parties);
+ long s = state;
+ 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));
}
- if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
+ 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);
+ }
+ else {
+ parent.doArrive((u == 0) ?
+ ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
+ if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase ||
+ ((int)(state >>> PHASE_SHIFT) != nextPhase &&
+ !UNSAFE.compareAndSwapLong(this, stateOffset,
+ s, next)))
+ reconcileState();
+ }
+ }
return phase;
+ }
}
}
/**
- * Arrives at the barrier, and deregisters from it, without
- * waiting for others.
+ * Implementation of register, bulkRegister
*
- * @return the current barrier phase number upon entry to
- * this method, or a negative value if terminated;
- * @throws IllegalStateException if the number of registered or
- * unarrived parties would become negative.
+ * @param registrations number to add to both parties and
+ * unarrived fields. Must be greater than zero.
*/
- public int arriveAndDeregister() { // Same as arrive, plus decrement parties
- final AtomicLong state = this.state;
+ private int doRegister(int registrations) {
+ // adjustment to state
+ long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
+ final Phaser parent = this.parent;
for (;;) {
- long s = state.get();
- int phase = phaseOf(s);
- int parties = partiesOf(s) - 1;
- int unarrived = unarrivedOf(s) - 1;
- if (parties < 0 || unarrived < 0)
- throw badBounds(parties, unarrived);
- if (unarrived == 0 && phase >= 0) {
- trip(phase, parties);
+ 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
+ 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;
+ }
+ }
+ }
}
- if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
- return phase;
}
}
/**
- * Arrives at the barrier and awaits others. Unlike other arrival
- * methods, this method returns the arrival index of the
- * caller. The caller tripping the barrier returns zero, the
- * previous caller 1, and so on.
- * @return the arrival index
- * @throws IllegalStateException if the number of unarrived
- * parties would become negative.
+ * Recursively resolves lagged phase propagation from root if necessary.
*/
- public int arriveAndAwaitAdvance() {
- final AtomicLong state = this.state;
- for (;;) {
- long s = state.get();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s) - 1;
- if (unarrived < 0)
- throw badBounds(parties, unarrived);
- if (unarrived == 0 && phase >= 0) {
- trip(phase, parties);
- return 0;
- }
- if (state.compareAndSet(s, stateFor(phase, parties, unarrived))) {
- awaitAdvance(phase);
- return unarrived;
+ 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 ((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;
}
/**
- * Awaits the phase of the barrier to advance from the given
- * value, or returns immediately if this barrier is terminated.
- * @param phase the phase on entry to this method
- * @return the phase on exit from this method
+ * Creates a new phaser without any initially registered parties,
+ * initial phase number 0, and no parent. Any thread using this
+ * phaser will need to first register for it.
+ */
+ public Phaser() {
+ this(null, 0);
+ }
+
+ /**
+ * 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
+ * @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, and without any
+ * initially registered parties. Any thread using this phaser
+ * will need to first register for it, at which point, if the
+ * given parent is non-null, this phaser will also be registered
+ * with the parent.
+ *
+ * Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
+ *
+ * @param parent the parent phaser
+ */
+ public Phaser(Phaser parent) {
+ this(parent, 0);
+ }
+
+ /**
+ * Creates a new phaser with the given parent and number of
+ * registered unarrived parties. If parent is non-null and
+ * the number of parties is non-zero, this phaser is registered
+ * with the parent.
+ *
+ * @param parent the parent phaser
+ * @param parties the number of parties required to trip barrier
+ * @throws IllegalArgumentException if parties less than zero
+ * or greater than the maximum number of parties supported
+ */
+ public Phaser(Phaser parent, int parties) {
+ if (parties >>> PARTIES_SHIFT != 0)
+ throw new IllegalArgumentException("Illegal number of parties");
+ int phase;
+ this.parent = parent;
+ if (parent != null) {
+ Phaser r = parent.root;
+ this.root = r;
+ this.evenQ = r.evenQ;
+ this.oddQ = r.oddQ;
+ phase = (parties == 0) ? parent.getPhase() : parent.doRegister(1);
+ }
+ else {
+ this.root = this;
+ this.evenQ = new AtomicReference();
+ this.oddQ = new AtomicReference();
+ phase = 0;
+ }
+ long p = (long)parties;
+ this.state = (((long)phase) << PHASE_SHIFT) | p | (p << PARTIES_SHIFT);
+ }
+
+ /**
+ * 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. 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
+ */
+ public int register() {
+ 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 wait until its completion before registering.
+ * If this phaser has a parent, and the given number of parities
+ * is greater than zero, and this phaser previously had no
+ * registered parties, this phaser is also registered with its
+ * parent.
+ *
+ * @param parties the number of additional parties required to trip barrier
+ * @return the arrival phase number to which this registration applied
+ * @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();
+ else if (parties == 0)
+ return getPhase();
+ return doRegister(parties);
+ }
+
+ /**
+ * Arrives at the barrier, but does not wait for others. (You can
+ * in turn wait for others via {@link #awaitAdvance}). It is a
+ * usage error for an unregistered party to invoke this
+ * method. However, it is possible that this error will result in
+ * an {code IllegalStateException} only when some other
+ * party arrives.
+ *
+ * @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() {
+ return doArrive(ONE_ARRIVAL);
+ }
+
+ /**
+ * Arrives at the barrier and deregisters from it without waiting
+ * for others. Deregistration reduces the number of parties
+ * required to trip the barrier in future phases. If this phaser
+ * has a parent, and deregistration causes this phaser to have
+ * zero parties, this phaser also arrives at and is deregistered
+ * from its parent. It is a usage error for an unregistered party
+ * to invoke this method. However, it is possible that this error
+ * will result in an {code IllegalStateException} only when some
+ * other party arrives.
+ *
+ * @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() {
+ return doArrive(ONE_ARRIVAL|ONE_PARTY);
+ }
+
+ /**
+ * 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 {@code
+ * awaitAdvance} method. If instead you need to deregister upon
+ * arrival, use {@link #arriveAndDeregister}. It is a usage error
+ * for an unregistered party to invoke this method. However, it is
+ * possible that this error will result in an {code
+ * IllegalStateException} only when some other party
+ * arrives.
+ *
+ * @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());
+ }
+
+ /**
+ * 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.
+ *
+ * @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
+ * @return the next arrival phase number, or a negative value
+ * if terminated or argument is negative
*/
public int awaitAdvance(int phase) {
if (phase < 0)
return phase;
- Thread current = Thread.currentThread();
- if (current instanceof ForkJoinWorkerThread)
- return helpingWait(phase);
- if (untimedWait(current, phase, false))
- current.interrupt();
- return phaseOf(state.get());
+ long s = (parent == null) ? state : reconcileState();
+ int p = (int)(s >>> PHASE_SHIFT);
+ return (p != phase) ? p : internalAwaitAdvance(phase, null);
}
/**
- * Awaits the phase of the barrier to advance from the given
- * value, or returns immediately if 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
+ * 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.
+ *
+ * @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
+ * @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 {
+ public int awaitAdvanceInterruptibly(int phase)
+ throws InterruptedException {
if (phase < 0)
return phase;
- Thread current = Thread.currentThread();
- if (current instanceof ForkJoinWorkerThread)
- return helpingWait(phase);
- else if (Thread.interrupted() || untimedWait(current, phase, true))
- throw new InterruptedException();
- else
- return phaseOf(state.get());
+ long s = (parent == null) ? state : reconcileState();
+ int p = (int)(s >>> PHASE_SHIFT);
+ if (p == phase) {
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ }
+ return p;
}
/**
- * Awaits the phase of the barrier to advance from the given value
- * or the given timeout elapses, or returns immediately if this
- * barrier is terminated.
- * @param phase the phase on entry to this method
- * @return the phase on exit from this method
+ * 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.
+ *
+ * @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
+ * @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
+ * if terminated or argument is negative
* @throws InterruptedException if thread interrupted while waiting
* @throws TimeoutException if timed out while waiting
*/
- public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
+ public int awaitAdvanceInterruptibly(int phase,
+ long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
if (phase < 0)
return phase;
- long nanos = unit.toNanos(timeout);
- Thread current = Thread.currentThread();
- if (current instanceof ForkJoinWorkerThread)
- return timedHelpingWait(phase, nanos);
- timedWait(current, phase, nanos);
- return phaseOf(state.get());
+ long s = (parent == null) ? state : reconcileState();
+ int p = (int)(s >>> PHASE_SHIFT);
+ if (p == phase) {
+ long nanos = unit.toNanos(timeout);
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else if (p == phase)
+ throw new TimeoutException();
+ }
+ return p;
}
/**
- * Forces this barrier to enter termination state. Counts of
- * arrived and registered parties are unaffected. This method may
- * be useful for coordinating recovery after one or more tasks
+ * Forces this barrier to enter termination state. Counts of
+ * arrived and registered parties are unaffected. If this phaser
+ * is a member of a tiered set of phasers, then all of the phasers
+ * in the set are terminated. If this phaser is already
+ * 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() {
- final AtomicLong state = this.state;
- for (;;) {
- long s = state.get();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s);
- if (phase < 0 ||
- state.compareAndSet(s, stateFor(-1, parties, unarrived))) {
- if (head.get() != null)
- releaseWaiters(-1);
+ // 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);
return;
}
}
}
/**
- * Resets the barrier with the given numbers of registered unarrived
- * parties and phase number 0. This method allows repeated reuse
- * of this barrier, but only if it is somehow known not to be in
- * use for other purposes.
- * @param parties the number of parties required to trip barrier.
- * @throws IllegalArgumentException if parties less than zero
- * or greater than the maximum number of parties supported.
- */
- public void reset(int parties) {
- if (parties < 0 || parties > ushortMask)
- throw new IllegalArgumentException("Illegal number of parties");
- state.set(stateFor(0, parties, parties));
- if (head.get() != null)
- releaseWaiters(0);
- }
-
- /**
* 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
*/
- public int getPhase() {
- return phaseOf(state.get());
+ public final int getPhase() {
+ return (int)(root.state >>> PHASE_SHIFT);
}
/**
* Returns the number of parties registered at this barrier.
+ *
* @return the number of parties
*/
public int getRegisteredParties() {
- return partiesOf(state.get());
+ return partiesOf(state);
}
/**
- * Returns the number of parties that have arrived at the current
- * phase of this barrier.
+ * Returns the number of registered parties that have arrived at
+ * the current phase of this barrier.
+ *
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(state.get());
+ return arrivedOf(parent==null? state : reconcileState());
}
/**
* Returns the number of registered parties that have not yet
* arrived at the current phase of this barrier.
+ *
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(state.get());
+ return unarrivedOf(parent==null? state : reconcileState());
+ }
+
+ /**
+ * Returns the parent of this phaser, or {@code null} if none.
+ *
+ * @return the parent of this phaser, or {@code null} if none
+ */
+ public Phaser getParent() {
+ return parent;
}
/**
- * Returns true if this barrier has been terminated.
- * @return true if this barrier has been terminated
+ * 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
+ */
+ public Phaser getRoot() {
+ return root;
+ }
+
+ /**
+ * Returns {@code true} if this barrier has been terminated.
+ *
+ * @return {@code true} if this barrier has been terminated
*/
public boolean isTerminated() {
- return phaseOf(state.get()) < 0;
+ return root.state < 0L;
}
/**
- * 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 true, then, rather than advance the
- * phase number, this barrier will be set to a final termination
- * state, and subsequent calls to isTerminated will
- * return true.
- *
- * The default version returns true when the number of
- * registered parties is zero. Normally, overrides that arrange
- * termination for other reasons should also preserve this
- * property.
+ * 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 effects of invoking
+ * arrival, registration, and waiting methods on this Phaser from
+ * within {@code onAdvance} are unspecified and should not be
+ * relied on.
+ *
+ *
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.
+ *
+ *
To support the most common use cases, the default
+ * implementation of this method returns {@code true} when the
+ * number of registered parties has become zero as the result of a
+ * party invoking {@code arriveAndDeregister}. You can disable
+ * this behavior, thus enabling continuation upon future
+ * registrations, by overriding this method to always return
+ * {@code false}:
+ *
+ *
{@code
+ * Phaser phaser = new Phaser() {
+ * protected boolean onAdvance(int phase, int parties) { return false; }
+ * }}
*
* @param phase the phase number on entering the barrier
- * @param registeredParties the current number of registered
- * parties.
- * @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;
}
/**
- * Returns a string identifying this barrier, as well as its
+ * Returns a string identifying this phaser, as well as its
* state. The state, in brackets, includes the String {@code
- * "phase ="} followed by the phase number, {@code "parties ="}
+ * "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 = state.get();
- return super.toString() + "[phase = " + phaseOf(s) + " parties = " + partiesOf(s) + " arrived = " + arrivedOf(s) + "]";
+ return stateToString(reconcileState());
}
- // methods for tripping and waiting
-
/**
- * Advance the current phase (or terminate)
+ * Implementation of toString and string-based error messages
*/
- private void trip(int phase, int parties) {
- int next = onAdvance(phase, parties)? -1 : ((phase + 1) & phaseMask);
- state.set(stateFor(next, parties, parties));
- if (head.get() != null)
- releaseWaiters(next);
+ private String stateToString(long s) {
+ return super.toString() +
+ "[phase = " + phaseOf(s) +
+ " parties = " + partiesOf(s) +
+ " arrived = " + arrivedOf(s) + "]";
}
- private int helpingWait(int phase) {
- final AtomicLong state = this.state;
+ // Waiting mechanics
+
+ /**
+ * Removes and signals threads from queue for phase.
+ */
+ private void releaseWaiters(int phase) {
+ AtomicReference head = queueFor(phase);
+ QNode q;
int p;
- while ((p = phaseOf(state.get())) == phase) {
- ForkJoinTask t = ForkJoinWorkerThread.pollTask();
- if (t != null) {
- if ((p = phaseOf(state.get())) == phase)
- t.exec();
- else { // push task and exit if barrier advanced
- t.fork();
- break;
- }
- }
+ while ((q = head.get()) != null &&
+ ((p = q.phase) == phase ||
+ (int)(root.state >>> PHASE_SHIFT) != p)) {
+ if (head.compareAndSet(q, q.next))
+ q.signal();
}
- return p;
}
- private int timedHelpingWait(int phase, long nanos) throws TimeoutException {
- final AtomicLong state = this.state;
- long lastTime = System.nanoTime();
+ /** The number of CPUs, for spin control */
+ private static final int NCPU = Runtime.getRuntime().availableProcessors();
+
+ /**
+ * 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. Plus, even on
+ * uniprocessors, there is at least one intervening Thread.yield
+ * before blocking. The value trades off good-citizenship vs big
+ * unnecessary slowdowns.
+ */
+ static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
+
+ /**
+ * Possibly blocks and waits for phase to advance unless aborted.
+ *
+ * @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 internalAwaitAdvance(int phase, QNode node) {
+ Phaser current = this; // to eventually wait at root if tiered
+ boolean queued = false; // true when node is enqueued
+ int lastUnarrived = -1; // to increase spins upon change
+ int spins = SPINS_PER_ARRIVAL;
+ long s;
int p;
- while ((p = phaseOf(state.get())) == phase) {
- long now = System.nanoTime();
- nanos -= now - lastTime;
- lastTime = now;
- if (nanos <= 0) {
- if ((p = phaseOf(state.get())) == phase)
- throw new TimeoutException();
- else
- break;
+ while ((p = (int)((s = current.state) >>> PHASE_SHIFT)) == phase) {
+ Phaser par;
+ int unarrived = (int)s & UNARRIVED_MASK;
+ if (unarrived != lastUnarrived) {
+ if (lastUnarrived == -1) // ensure old queue clean
+ releaseWaiters(phase-1);
+ if ((lastUnarrived = unarrived) < NCPU)
+ spins += SPINS_PER_ARRIVAL;
}
- ForkJoinTask t = ForkJoinWorkerThread.pollTask();
- if (t != null) {
- if ((p = phaseOf(state.get())) == phase)
- t.exec();
- else { // push task and exit if barrier advanced
- t.fork();
+ else if (unarrived == 0 && (par = current.parent) != null) {
+ current = par; // if all arrived, use parent
+ par = par.parent;
+ lastUnarrived = -1;
+ }
+ else if (spins > 0) {
+ if (--spins == (SPINS_PER_ARRIVAL >>> 1))
+ Thread.yield(); // yield midway through spin
+ }
+ else if (node == null) // must be noninterruptible
+ node = new QNode(this, phase, false, false, 0L);
+ else if (node.isReleasable()) {
+ if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
break;
+ else
+ return phase; // aborted
+ }
+ else if (!queued) { // push onto queue
+ AtomicReference head = queueFor(phase);
+ QNode q = head.get();
+ if (q == null || q.phase == phase) {
+ node.next = q;
+ if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
+ break; // recheck to avoid stale enqueue
+ else
+ queued = head.compareAndSet(q, node);
+ }
+ }
+ else {
+ try {
+ ForkJoinPool.managedBlock(node);
+ } catch (InterruptedException ie) {
+ node.wasInterrupted = true;
}
}
}
+ releaseWaiters(phase);
+ if (node != null)
+ node.onRelease();
return p;
}
/**
- * Wait nodes for Treiber stack representing wait queue for non-FJ
- * tasks. The waiting scheme is an adaptation of the one used in
- * forkjoin.PoolBarrier.
+ * Wait nodes for Treiber stack representing wait queue
*/
- static final class QNode {
- QNode next;
- volatile Thread thread; // nulled to cancel wait
+ static final class QNode implements ForkJoinPool.ManagedBlocker {
+ final Phaser phaser;
final int phase;
- QNode(Thread t, int c) {
- thread = t;
- phase = c;
+ 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();
}
- }
- private void releaseWaiters(int currentPhase) {
- final AtomicReference head = this.head;
- QNode p;
- while ((p = head.get()) != null && p.phase != currentPhase) {
- if (head.compareAndSet(p, null)) {
- do {
- Thread t = p.thread;
- if (t != null) {
- p.thread = null;
- LockSupport.unpark(t);
+ public boolean isReleasable() {
+ Thread t = thread;
+ if (t != null) {
+ if (phaser.getPhase() != phase)
+ t = null;
+ else {
+ if (Thread.interrupted())
+ wasInterrupted = true;
+ if (interruptible && wasInterrupted)
+ t = null;
+ else if (timed) {
+ if (nanos > 0) {
+ long now = System.nanoTime();
+ nanos -= now - lastTime;
+ lastTime = now;
+ }
+ if (nanos <= 0)
+ t = null;
}
- } while ((p = p.next) != null);
+ }
+ if (t != null)
+ return false;
+ thread = null;
}
+ return true;
}
- }
- /** The number of CPUs, for spin control */
- static final int NCPUS = Runtime.getRuntime().availableProcessors();
+ public boolean block() {
+ if (isReleasable())
+ return true;
+ else if (!timed)
+ LockSupport.park(this);
+ else if (nanos > 0)
+ LockSupport.parkNanos(this, nanos);
+ return isReleasable();
+ }
- /**
- * The number of times to spin before blocking in timed waits.
- * The value is empirically derived.
- */
- static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
+ void signal() {
+ Thread t = thread;
+ if (t != null) {
+ thread = null;
+ LockSupport.unpark(t);
+ }
+ }
- /**
- * 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;
+ void onRelease() { // actions upon return from internalAwaitAdvance
+ if (!interruptible && wasInterrupted)
+ Thread.currentThread().interrupt();
+ if (thread != null)
+ thread = null;
+ }
- /**
- * The number of nanoseconds for which it is faster to spin
- * rather than to use timed park. A rough estimate suffices.
- */
- static final long spinForTimeoutThreshold = 1000L;
+ }
- /**
- * Enqueues node and waits unless aborted or signalled.
- */
- private boolean untimedWait(Thread thread, int currentPhase,
- boolean abortOnInterrupt) {
- final AtomicReference head = this.head;
- final AtomicLong state = this.state;
- boolean wasInterrupted = false;
- QNode node = null;
- boolean queued = false;
- int spins = maxUntimedSpins;
- while (phaseOf(state.get()) == currentPhase) {
- QNode h;
- if (node != null && queued) {
- if (node.thread != null) {
- LockSupport.park();
- if (Thread.interrupted()) {
- wasInterrupted = true;
- if (abortOnInterrupt)
- break;
- }
- }
- }
- else if ((h = head.get()) != null && h.phase != currentPhase) {
- if (phaseOf(state.get()) == currentPhase) { // must recheck
- if (head.compareAndSet(h, h.next)) {
- Thread t = h.thread; // help clear out old waiters
- if (t != null) {
- h.thread = null;
- LockSupport.unpark(t);
- }
- }
- }
- else
- break;
- }
- else if (node != null)
- queued = head.compareAndSet(node.next = h, node);
- else if (spins <= 0)
- node = new QNode(thread, currentPhase);
- else
- --spins;
+ // Unsafe mechanics
+
+ private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+ private static final long stateOffset =
+ objectFieldOffset("state", Phaser.class);
+
+ private static long objectFieldOffset(String field, Class klazz) {
+ try {
+ return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+ } catch (NoSuchFieldException e) {
+ // Convert Exception to corresponding Error
+ NoSuchFieldError error = new NoSuchFieldError(field);
+ error.initCause(e);
+ throw error;
}
- if (node != null)
- node.thread = null;
- return wasInterrupted;
}
/**
- * Messier timeout version
+ * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
+ * Replace with a simple call to Unsafe.getUnsafe when integrating
+ * into a jdk.
+ *
+ * @return a sun.misc.Unsafe
*/
- private void timedWait(Thread thread, int currentPhase, long nanos)
- throws InterruptedException, TimeoutException {
- final AtomicReference head = this.head;
- final AtomicLong state = this.state;
- long lastTime = System.nanoTime();
- QNode node = null;
- boolean queued = false;
- int spins = maxTimedSpins;
- while (phaseOf(state.get()) == currentPhase) {
- QNode h;
- long now = System.nanoTime();
- nanos -= now - lastTime;
- lastTime = now;
- if (nanos <= 0) {
- if (node != null)
- node.thread = null;
- if (phaseOf(state.get()) == currentPhase)
- throw new TimeoutException();
- else
- break;
- }
- else if (node != null && queued) {
- if (node.thread != null &&
- nanos > spinForTimeoutThreshold) {
- // LockSupport.parkNanos(this, nanos);
- LockSupport.parkNanos(nanos);
- if (Thread.interrupted()) {
- node.thread = null;
- throw new InterruptedException();
- }
- }
+ private static sun.misc.Unsafe getUnsafe() {
+ try {
+ return sun.misc.Unsafe.getUnsafe();
+ } catch (SecurityException se) {
+ try {
+ return java.security.AccessController.doPrivileged
+ (new java.security
+ .PrivilegedExceptionAction() {
+ public sun.misc.Unsafe run() throws Exception {
+ java.lang.reflect.Field f = sun.misc
+ .Unsafe.class.getDeclaredField("theUnsafe");
+ f.setAccessible(true);
+ return (sun.misc.Unsafe) f.get(null);
+ }});
+ } catch (java.security.PrivilegedActionException e) {
+ throw new RuntimeException("Could not initialize intrinsics",
+ e.getCause());
}
- else if ((h = head.get()) != null && h.phase != currentPhase) {
- if (phaseOf(state.get()) == currentPhase) { // must recheck
- if (head.compareAndSet(h, h.next)) {
- Thread t = h.thread; // help clear out old waiters
- if (t != null) {
- h.thread = null;
- LockSupport.unpark(t);
- }
- }
- }
- else
- break;
- }
- else if (node != null)
- queued = head.compareAndSet(node.next = h, node);
- else if (spins <= 0)
- node = new QNode(thread, currentPhase);
- else
- --spins;
}
- if (node != null)
- node.thread = null;
}
-
}
-