--- jsr166/src/jsr166y/Phaser.java 2010/07/07 19:52:32 1.47 +++ jsr166/src/jsr166y/Phaser.java 2010/11/29 00:52:28 1.62 @@ -6,8 +6,8 @@ package jsr166y; -import java.util.concurrent.*; - +import java.util.concurrent.TimeUnit; +import java.util.concurrent.TimeoutException; import java.util.concurrent.atomic.AtomicReference; import java.util.concurrent.locks.LockSupport; @@ -18,7 +18,7 @@ import java.util.concurrent.locks.LockSu * but supporting more flexible usage. * *
Registration. Unlike the case for other barriers, the - * number of parties registered to synchronize on a phaser + * 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 @@ -76,26 +76,28 @@ import java.util.concurrent.locks.LockSu * *
Termination. A {@code Phaser} may enter a * termination state in which all synchronization methods - * immediately return without updating phaser state or waiting for + * 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 + * 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., arranged - * in tree structures) to reduce contention. Phasers with large - * numbers of parties that would otherwise experience heavy + *
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 + * 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 @@ -109,9 +111,9 @@ import java.util.concurrent.locks.LockSu *
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) { @@ -181,10 +183,10 @@ import java.util.concurrent.locks.LockSu * }}
To create a set of tasks using a tree of phasers, + *
To create a set of tasks using a tree of Phasers, * you could use code of the following form, assuming a - * Task class with a constructor accepting a phaser that - * it registers for upon construction: + * Task class with a constructor accepting a Phaser that + * it registers with upon construction: * *
{@code * void build(Task[] actions, int lo, int hi, Phaser ph) { @@ -207,12 +209,10 @@ 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
- * should create tiered phasers to accommodate arbitrarily large sets
+ * should create tiered Phasers to accommodate arbitrarily large sets
* of participants.
*
* @since 1.7
@@ -229,59 +229,47 @@ public class Phaser {
* 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 (atomic) long. Termination uses the sign
* bit of 32 bit representation of phase, so phase is set to -1 on
* termination. Good performance relies on keeping state decoding
* and encoding simple, and keeping race windows short.
- *
- * Note: there are some cheats in arrive() that rely on unarrived
- * count being lowest 16 bits.
*/
private volatile long state;
- private static final int ushortMask = 0xffff;
- private static final int phaseMask = 0x7fffffff;
+ private static final int MAX_PARTIES = 0xffff;
+ private static final int MAX_PHASE = 0x7fffffff;
+ private static final int PARTIES_SHIFT = 16;
+ private static final int PHASE_SHIFT = 32;
+ private static final int UNARRIVED_MASK = 0xffff; // to mask ints
+ private static final long PARTIES_MASK = 0xffff0000L; // to mask longs
+ private static final long ONE_ARRIVAL = 1L;
+ private static final long ONE_PARTY = 1L << PARTIES_SHIFT;
+ private static final long TERMINATION_BIT = 1L << 63;
+
+ // The following unpacking methods are usually manually inlined
private static int unarrivedOf(long s) {
- return (int) (s & ushortMask);
+ return (int)s & UNARRIVED_MASK;
}
private static int partiesOf(long s) {
- return ((int) s) >>> 16;
+ return (int)s >>> PARTIES_SHIFT;
}
private static int phaseOf(long s) {
- return (int) (s >>> 32);
+ return (int) (s >>> PHASE_SHIFT);
}
private static int arrivedOf(long s) {
return partiesOf(s) - unarrivedOf(s);
}
- private static long stateFor(int phase, int parties, int unarrived) {
- return ((((long) phase) << 32) | (((long) parties) << 16) |
- (long) unarrived);
- }
-
- private static long trippedStateFor(int phase, int parties) {
- long lp = (long) parties;
- return (((long) phase) << 32) | (lp << 16) | lp;
- }
-
- /**
- * Returns message string for bad bounds exceptions.
- */
- private static String badBounds(int parties, int unarrived) {
- return ("Attempt to set " + unarrived +
- " unarrived of " + parties + " parties");
- }
-
/**
* The parent of this phaser, or null if none
*/
@@ -293,62 +281,163 @@ public class Phaser {
*/
private final Phaser root;
- // Wait queues
-
/**
* Heads of Treiber stacks for waiting threads. To eliminate
- * contention while releasing some threads while adding others, we
+ * contention when releasing some threads while adding others, we
* use two of them, alternating across even and odd phases.
+ * Subphasers share queues with root to speed up releases.
*/
- private final AtomicReference It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this Phaser, if ever.
*
* @return the arrival phase number, or a negative value if terminated
* @throws IllegalStateException if not terminated and the number
* of unarrived parties would become negative
*/
public int arrive() {
- int phase;
- for (;;) {
- long s = state;
- phase = phaseOf(s);
- if (phase < 0)
- break;
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s) - 1;
- if (unarrived > 0) { // Not the last arrival
- if (casState(s, s - 1)) // s-1 adds one arrival
- break;
- }
- else if (unarrived == 0) { // the last arrival
- Phaser par = parent;
- if (par == null) { // directly trip
- if (casState
- (s,
- trippedStateFor(onAdvance(phase, parties) ? -1 :
- ((phase + 1) & phaseMask), parties))) {
- releaseWaiters(phase);
- break;
- }
- }
- else { // cascade to parent
- if (casState(s, s - 1)) { // zeroes unarrived
- par.arrive();
- reconcileState();
- break;
- }
- }
- }
- else if (phase != phaseOf(root.state)) // or if unreconciled
- reconcileState();
- else
- throw new IllegalStateException(badBounds(parties, unarrived));
- }
- return phase;
+ 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 an unenforced usage error for an
- * unregistered party to invoke this method.
+ * for others to arrive. 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 is also deregistered from its
+ * parent.
+ *
+ * It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this Phaser, if ever.
*
* @return the arrival phase number, or a negative value if terminated
* @throws IllegalStateException if not terminated and the number
* of registered or unarrived parties would become negative
*/
public int arriveAndDeregister() {
- // similar code to arrive, but too different to merge
- Phaser par = parent;
- int phase;
- for (;;) {
- long s = state;
- phase = phaseOf(s);
- if (phase < 0)
- break;
- int parties = partiesOf(s) - 1;
- int unarrived = unarrivedOf(s) - 1;
- if (parties >= 0) {
- if (unarrived > 0 || (unarrived == 0 && par != null)) {
- if (casState
- (s,
- stateFor(phase, parties, unarrived))) {
- if (unarrived == 0) {
- par.arriveAndDeregister();
- reconcileState();
- }
- break;
- }
- continue;
- }
- if (unarrived == 0) {
- if (casState
- (s,
- trippedStateFor(onAdvance(phase, parties) ? -1 :
- ((phase + 1) & phaseMask), parties))) {
- releaseWaiters(phase);
- break;
- }
- continue;
- }
- if (par != null && phase != phaseOf(root.state)) {
- reconcileState();
- continue;
- }
- }
- throw new IllegalStateException(badBounds(parties, unarrived));
- }
- return phase;
+ 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 awaitAdvance
- * method. If instead you need to deregister upon arrival use
- * {@code arriveAndDeregister}. It is an unenforced usage error
- * for an unregistered party to invoke this method.
+ * construction using one of the other forms of the {@code
+ * awaitAdvance} method. If instead you need to deregister upon
+ * arrival, use {@code awaitAdvance(arriveAndDeregister())}.
+ *
+ * It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this Phaser, if ever.
*
* @return the arrival phase number, or a negative number if terminated
* @throws IllegalStateException if not terminated and the number
* of unarrived parties would become negative
*/
public int arriveAndAwaitAdvance() {
- return awaitAdvance(arrive());
+ return awaitAdvance(doArrive(ONE_ARRIVAL));
}
/**
* Awaits the phase of the barrier to advance from the given phase
* value, returning immediately if the current phase of the
* barrier is not equal to the given phase value or this barrier
- * is terminated. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * is terminated.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
@@ -590,16 +603,14 @@ public class Phaser {
* if terminated or argument is negative
*/
public int awaitAdvance(int phase) {
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
- 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);
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
+ return rt.internalAwaitAdvance(phase, null);
+ return p;
}
/**
@@ -607,8 +618,7 @@ public class Phaser {
* value, throwing {@code InterruptedException} if interrupted
* while waiting, or returning immediately if the current phase of
* the barrier is not equal to the given phase value or this
- * barrier is terminated. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * barrier is terminated.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
@@ -619,15 +629,18 @@ public class Phaser {
*/
public int awaitAdvanceInterruptibly(int phase)
throws InterruptedException {
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
- return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase);
- return interruptibleWait(phase);
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = rt.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ }
+ return p;
}
/**
@@ -636,8 +649,7 @@ public class Phaser {
* InterruptedException} if interrupted while waiting, or
* returning immediately if the current phase of the barrier is
* not equal to the given phase value or this barrier is
- * terminated. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * terminated.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
@@ -654,36 +666,41 @@ public class Phaser {
public int awaitAdvanceInterruptibly(int phase,
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
- if (p != phase)
- return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase, timeout, unit);
- return timedWait(phase, unit.toNanos(timeout));
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = rt.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else if (p == phase)
+ throw new TimeoutException();
+ }
+ return p;
}
/**
- * Forces this barrier to enter termination state. Counts of
- * arrived and registered parties are unaffected. If this phaser
- * has a parent, it too is terminated. This method may be useful
- * for coordinating recovery after one or more tasks encounter
- * unexpected exceptions.
+ * 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() {
- for (;;) {
- long s = getReconciledState();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s);
- if (phase < 0 ||
- casState(s, stateFor(-1, parties, unarrived))) {
- releaseWaiters(0);
+ // Only need to change root state
+ final Phaser root = this.root;
+ long s;
+ while ((s = root.state) >= 0) {
+ if (UNSAFE.compareAndSwapLong(root, stateOffset,
+ s, s | TERMINATION_BIT)) {
+ releaseWaiters(0); // signal all threads
releaseWaiters(1);
- if (parent != null)
- parent.forceTermination();
return;
}
}
@@ -697,7 +714,7 @@ public class Phaser {
* @return the phase number, or a negative value if terminated
*/
public final int getPhase() {
- return phaseOf(getReconciledState());
+ return (int)(root.state >>> PHASE_SHIFT);
}
/**
@@ -716,7 +733,11 @@ public class Phaser {
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(state);
+ long s = state;
+ int u = unarrivedOf(s); // only reconcile if possibly needed
+ return (u != 0 || parent == null) ?
+ partiesOf(s) - u :
+ arrivedOf(reconcileState());
}
/**
@@ -726,23 +747,24 @@ public class Phaser {
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(state);
+ int u = unarrivedOf(state);
+ return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
}
/**
- * Returns the parent of this phaser, or {@code null} if none.
+ * Returns the parent of this Phaser, or {@code null} if none.
*
- * @return 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 the root ancestor of this phaser, which is the same as
- * this phaser if it has no parent.
+ * 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;
@@ -754,7 +776,7 @@ public class Phaser {
* @return {@code true} if this barrier has been terminated
*/
public boolean isTerminated() {
- return getPhase() < 0;
+ return root.state < 0L;
}
/**
@@ -769,36 +791,39 @@ public class Phaser {
* 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. (When called from within
- * an implementation of {@code onAdvance} the values returned by
- * methods such as {@code getPhase} may or may not reliably
- * indicate the state to which this transition applies.)
- *
- * 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 only sensible
- * to do so in designs where all parties register before any
- * arrive, and all {@link #awaitAdvance} at each phase.
- * Otherwise, you cannot ensure lack of interference from other
- * parties during the invocation of this method. Additionally,
- * method {@code onAdvance} may be invoked more than once per
- * transition if registrations are intermixed with arrivals.
+ * 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 {@code true} if this barrier should terminate
*/
protected boolean onAdvance(int phase, int registeredParties) {
- return registeredParties <= 0;
+ return registeredParties == 0;
}
/**
- * Returns a string identifying this phaser, as well as its
+ * Returns a string identifying this Phaser, as well as its
* state. The state, in brackets, includes the String {@code
* "phase = "} followed by the phase number, {@code "parties = "}
* followed by the number of registered parties, and {@code
@@ -807,14 +832,116 @@ public class Phaser {
* @return a string identifying this barrier, as well as its state
*/
public String toString() {
- long s = getReconciledState();
+ return stateToString(reconcileState());
+ }
+
+ /**
+ * Implementation of toString and string-based error messages
+ */
+ private String stateToString(long s) {
return super.toString() +
"[phase = " + phaseOf(s) +
" parties = " + partiesOf(s) +
" arrived = " + arrivedOf(s) + "]";
}
- // methods for waiting
+ // Waiting mechanics
+
+ /**
+ * Removes and signals threads from queue for phase.
+ */
+ private void releaseWaiters(int phase) {
+ AtomicReference