Phasers ensure lack of starvation when used by ForkJoinTasks.
- *
- *
+ * 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 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:
+ *
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 list) {
+ * void runTasks(List tasks) {
* final Phaser phaser = new Phaser(1); // "1" to register self
- * for (Runnable r : list) {
+ * // create and start threads
+ * for (Runnable task : tasks) {
* phaser.register();
* new Thread() {
* public void run() {
* phaser.arriveAndAwaitAdvance(); // await all creation
- * r.run();
- * phaser.arriveAndDeregister(); // signal completion
+ * task.run();
* }
* }.start();
* }
*
- * doSomethingOnBehalfOfWorkers();
- * phaser.arrive(); // allow threads to start
- * int p = phaser.arriveAndDeregister(); // deregister self ...
- * p = phaser.awaitAdvance(p); // ... and await arrival
- * otherActions(); // do other things while tasks execute
- * phaser.awaitAdvance(p); // await final completion
+ * // 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 list, final int iterations) {
+ * void startTasks(List tasks, final int iterations) {
* final Phaser phaser = new Phaser() {
- * public boolean onAdvance(int phase, int registeredParties) {
+ * protected boolean onAdvance(int phase, int registeredParties) {
* return phase >= iterations || registeredParties == 0;
* }
* };
* phaser.register();
- * for (Runnable r : list) {
+ * for (final Runnable task : tasks) {
* phaser.register();
* new Thread() {
* public void run() {
* do {
- * r.run();
+ * task.run();
* phaser.arriveAndAwaitAdvance();
- * } while(!phaser.isTerminated();
+ * } while (!phaser.isTerminated());
* }
* }.start();
* }
* phaser.arriveAndDeregister(); // deregister self, don't wait
* }}
*
- * To create a set of tasks using a tree of Phasers,
+ * If the main task must later await termination, it
+ * may re-register and then execute a similar loop:
+ *
{@code
+ * // ...
+ * phaser.register();
+ * while (!phaser.isTerminated())
+ * phaser.arriveAndAwaitAdvance();}
+ *
+ * Related constructions may be used to await particular phase numbers
+ * in contexts where you are sure that the phase will never wrap around
+ * {@code Integer.MAX_VALUE}. For example:
+ *
+ *
{@code
+ * void awaitPhase(Phaser phaser, int phase) {
+ * int p = phaser.register(); // assumes caller not already registered
+ * while (p < phase) {
+ * if (phaser.isTerminated())
+ * // ... deal with unexpected termination
+ * else
+ * p = phaser.arriveAndAwaitAdvance();
+ * }
+ * phaser.arriveAndDeregister();
+ * }}
+ *
+ *
+ * To create a set of tasks using a tree of phasers,
* you could use code of the following form, assuming a
- * Task class with a constructor accepting a Phaser that
- * it registers for upon construction:
+ * Task class with a constructor accepting a phaser that
+ * it registers with upon construction:
+ *
*
{@code
- * void build(Task[] actions, int lo, int hi, Phaser b) {
- * int step = (hi - lo) / TASKS_PER_PHASER;
- * if (step > 1) {
- * int i = lo;
- * while (i < hi) {
- * int r = Math.min(i + step, hi);
- * build(actions, i, r, new Phaser(b));
- * i = r;
+ * void build(Task[] actions, int lo, int hi, Phaser ph) {
+ * if (hi - lo > TASKS_PER_PHASER) {
+ * for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
+ * int j = Math.min(i + TASKS_PER_PHASER, hi);
+ * build(actions, i, j, new Phaser(ph));
* }
* } else {
* for (int i = lo; i < hi; ++i)
- * actions[i] = new Task(b);
- * // assumes new Task(b) performs b.register()
+ * actions[i] = new Task(ph);
+ * // assumes new Task(ph) performs ph.register()
* }
* }
* // .. initially called, for n tasks via
@@ -167,11 +207,9 @@ 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 IllegalStateExceptions. However, you can and
+ * parties result in {@code IllegalStateException}. However, you can and
* should create tiered phasers to accommodate arbitrarily large sets
* of participants.
*
@@ -189,127 +227,202 @@ 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 ushortBits = 16;
- private static final int ushortMask = 0xffff;
- private static final int phaseMask = 0x7fffffff;
+ private static final int MAX_COUNT = 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 long UNARRIVED_MASK = 0xffffL;
+ private static final long PARTIES_MASK = 0xffff0000L;
+ private static final long ONE_ARRIVAL = 1L;
+ private static final long ONE_PARTY = 1L << PARTIES_SHIFT;
+ private static final long TERMINATION_PHASE = -1L << PHASE_SHIFT;
+
+ // 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_MASK)) >>> 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
*/
private final Phaser parent;
/**
- * The root of Phaser tree. Equals this if not in a tree. Used to
+ * The root of phaser tree. Equals this if not in a tree. Used to
* support faster state push-down.
*/
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 evenQ = new AtomicReference();
- private final AtomicReference oddQ = new AtomicReference();
+ private final AtomicReference evenQ;
+ private final AtomicReference oddQ;
private AtomicReference queueFor(int phase) {
return ((phase & 1) == 0) ? evenQ : oddQ;
}
/**
- * Returns current state, first resolving lagged propagation from
- * root if necessary.
+ * 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.
+ *
+ * @param adj - adjustment to apply to state -- either
+ * ONE_ARRIVAL (for arrive) or
+ * ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
+ */
+ private int doArrive(long adj) {
+ long s;
+ int phase, unarrived;
+ while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0) {
+ if ((unarrived = (int)(s & UNARRIVED_MASK)) != 0) {
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s -= adj)) {
+ if (unarrived == 1) {
+ Phaser par;
+ 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;
+ if ((par = parent) == null) {
+ UNSAFE.compareAndSwapLong
+ (this, stateOffset, s, onAdvance(phase, u)?
+ next | TERMINATION_PHASE : next);
+ releaseWaiters(phase);
+ }
+ else {
+ par.doArrive(u == 0?
+ ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
+ if ((int)(par.state >>> PHASE_SHIFT) != nextPhase ||
+ ((int)(state >>> PHASE_SHIFT) != nextPhase &&
+ !UNSAFE.compareAndSwapLong(this, stateOffset,
+ s, next)))
+ reconcileState();
+ }
+ }
+ break;
+ }
+ }
+ else if (state == s && reconcileState() == s) // recheck
+ throw new IllegalStateException(badArrive());
+ }
+ return phase;
+ }
+
+ /**
+ * Returns message string for bounds exceptions on arrival.
+ * Declared out of-line from doArrive to reduce string op bulk.
*/
- private long getReconciledState() {
- return (parent == null) ? state : reconcileState();
+ private String badArrive() {
+ return ("Attempted arrival of unregistered party for " +
+ this.toString());
}
/**
- * Recursively resolves state.
+ * Implementation of register, bulkRegister
+ *
+ * @param registrations number to add to both parties and unarrived fields
+ */
+ private int doRegister(int registrations) {
+ long adj = (long)registrations; // adjustment to state
+ adj |= adj << PARTIES_SHIFT;
+ Phaser par = parent;
+ long s;
+ int phase;
+ while ((phase = (int)((s = (par == null? state : reconcileState()))
+ >>> PHASE_SHIFT)) >= 0) {
+ int parties = ((int)(s & PARTIES_MASK)) >>> PARTIES_SHIFT;
+ if (parties != 0 && (s & UNARRIVED_MASK) == 0)
+ internalAwaitAdvance(phase, null); // wait for onAdvance
+ else if (parties + registrations > MAX_COUNT)
+ throw new IllegalStateException(badRegister());
+ else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
+ break;
+ }
+ return phase;
+ }
+
+ /**
+ * Returns message string for bounds exceptions on registration
+ */
+ private String badRegister() {
+ return ("Attempt to register more than " + MAX_COUNT + " parties for "+
+ this.toString());
+ }
+
+ /**
+ * Recursively resolves lagged phase propagation from root if
+ * necessary.
*/
private long reconcileState() {
- Phaser p = parent;
- long s = state;
- if (p != null) {
- while (unarrivedOf(s) == 0 && phaseOf(s) != phaseOf(root.state)) {
- long parentState = p.getReconciledState();
- int parentPhase = phaseOf(parentState);
- int phase = phaseOf(s = state);
- if (phase != parentPhase) {
- long next = trippedStateFor(parentPhase, partiesOf(s));
- if (casState(s, next)) {
- releaseWaiters(phase);
- s = next;
- }
+ Phaser par = parent;
+ if (par == null)
+ return state;
+ Phaser rt = root;
+ long s;
+ int phase, rPhase;
+ while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0 &&
+ (rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
+ if (rPhase < 0 || (s & UNARRIVED_MASK) == 0) {
+ long ps = par.parent == null? par.state : par.reconcileState();
+ int pPhase = (int)(ps >>> PHASE_SHIFT);
+ if (pPhase < 0 || pPhase == ((phase + 1) & MAX_PHASE)) {
+ if (state != s)
+ continue;
+ long p = s & PARTIES_MASK;
+ long next = ((((long) pPhase) << PHASE_SHIFT) |
+ (p >>> PARTIES_SHIFT) | p);
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
+ return next;
}
}
+ if (state == s)
+ releaseWaiters(phase); // help release others
}
return s;
}
/**
- * Creates a new Phaser without any initially registered parties,
+ * 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.
+ * phaser will need to first register for it.
*/
public Phaser() {
- this(null);
+ this(null, 0);
}
/**
- * Creates a new Phaser with the given numbers of registered
+ * Creates a new phaser with the given number of registered
* unarrived parties, initial phase number 0, and no parent.
*
* @param parties the number of parties required to trip barrier
@@ -321,7 +434,7 @@ public class Phaser {
}
/**
- * Creates a new Phaser with the given parent, without any
+ * Creates a new phaser with the given parent, without any
* initially registered parties. If parent is non-null this phaser
* is registered with the parent and its initial phase number is
* the same as that of parent phaser.
@@ -329,19 +442,11 @@ public class Phaser {
* @param parent the parent phaser
*/
public Phaser(Phaser parent) {
- int phase = 0;
- this.parent = parent;
- if (parent != null) {
- this.root = parent.root;
- phase = parent.register();
- }
- else
- this.root = this;
- this.state = trippedStateFor(phase, 0);
+ this(parent, 0);
}
/**
- * Creates a new Phaser with the given parent and numbers of
+ * Creates a new phaser with the given parent and number of
* registered unarrived parties. If parent is non-null, this phaser
* is registered with the parent and its initial phase number is
* the same as that of parent phaser.
@@ -352,23 +457,33 @@ public class Phaser {
* or greater than the maximum number of parties supported
*/
public Phaser(Phaser parent, int parties) {
- if (parties < 0 || parties > ushortMask)
+ if (parties < 0 || parties > MAX_COUNT)
throw new IllegalArgumentException("Illegal number of parties");
- int phase = 0;
+ int phase;
this.parent = parent;
if (parent != null) {
- this.root = parent.root;
+ Phaser r = parent.root;
+ this.root = r;
+ this.evenQ = r.evenQ;
+ this.oddQ = r.oddQ;
phase = parent.register();
}
- else
+ else {
this.root = this;
- this.state = trippedStateFor(phase, parties);
+ 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.
*
- * @return the current barrier phase number upon registration
+ * @return the arrival phase number to which this registration applied
* @throws IllegalStateException if attempting to register more
* than the maximum supported number of parties
*/
@@ -378,153 +493,66 @@ public class Phaser {
/**
* Adds the given number of new unarrived parties to this phaser.
+ * If an ongoing invocation of {@link #onAdvance} is in progress,
+ * this method may wait until its completion before registering.
*
- * @param parties the number of parties required to trip barrier
- * @return the current barrier phase number upon registration
+ * @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();
+ if (parties > MAX_COUNT)
+ throw new IllegalStateException(badRegister());
if (parties == 0)
return getPhase();
return doRegister(parties);
}
/**
- * Shared code for register, bulkRegister
- */
- private int doRegister(int registrations) {
- int phase;
- for (;;) {
- long s = getReconciledState();
- phase = phaseOf(s);
- int unarrived = unarrivedOf(s) + registrations;
- int parties = partiesOf(s) + registrations;
- if (phase < 0)
- break;
- if (parties > ushortMask || unarrived > ushortMask)
- throw new IllegalStateException(badBounds(parties, unarrived));
- if (phase == phaseOf(root.state) &&
- casState(s, stateFor(phase, parties, unarrived)))
- break;
- }
- return phase;
- }
-
- /**
* Arrives at the barrier, but does not wait for others. (You can
- * in turn wait for others via {@link #awaitAdvance}).
+ * in turn wait for others via {@link #awaitAdvance}). It is an
+ * unenforced usage error for an unregistered party to invoke this
+ * method.
*
- * @return the barrier phase number upon entry to this method, or a
- * negative value if terminated
+ * @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 number of parties
+ * 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 is also deregistered from its parent.
+ * 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.
*
- * @return the current barrier phase number upon entry to
- * this method, or a negative value if terminated
+ * @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 instead need to
- * await with interruption of timeout, and/or deregister upon
- * arrival, you can arrange them using analogous constructions.
+ * 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 an unenforced
+ * usage error for an unregistered party to invoke this method.
*
- * @return the phase on entry to this method
+ * @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
*/
@@ -533,71 +561,92 @@ public class Phaser {
}
/**
- * Awaits the phase of the barrier to advance from the given
- * value, or returns immediately if argument is negative or 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, 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;
- long s = getReconciledState();
- int p = phaseOf(s);
+ int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
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);
+ return internalAwaitAdvance(phase, null);
}
/**
- * Awaits the phase of the barrier to advance from the given
- * value, or returns immediately if argument is negative or this
- * barrier is terminated, or throws InterruptedException if
- * interrupted while waiting.
+ * 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 the phase on entry to this method
- * @return the phase on exit from this method
+ * @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 {
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
+ int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
if (p != phase)
return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase);
- return interruptibleWait(phase);
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else
+ return p;
}
/**
- * Awaits the phase of the barrier to advance from the given value
- * or the given timeout elapses, or returns immediately if
- * argument is negative or 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)
throws InterruptedException, TimeoutException {
+ long nanos = unit.toNanos(timeout);
if (phase < 0)
return phase;
- long s = getReconciledState();
- int p = phaseOf(s);
+ int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
if (p != phase)
return p;
- if (unarrivedOf(s) == 0 && parent != null)
- parent.awaitAdvanceInterruptibly(phase, timeout, unit);
- return timedWait(phase, 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();
+ else
+ return p;
}
/**
@@ -608,20 +657,13 @@ public class Phaser {
* unexpected exceptions.
*/
public void forceTermination() {
- for (;;) {
- long s = getReconciledState();
- int phase = phaseOf(s);
- int parties = partiesOf(s);
- int unarrived = unarrivedOf(s);
- if (phase < 0 ||
- casState(s, stateFor(-1, parties, unarrived))) {
- releaseWaiters(0);
- releaseWaiters(1);
- if (parent != null)
- parent.forceTermination();
- return;
- }
- }
+ Phaser r = root; // force at root then reconcile
+ long s;
+ while ((s = r.state) >= 0)
+ UNSAFE.compareAndSwapLong(r, stateOffset, s, s | TERMINATION_PHASE);
+ reconcileState();
+ releaseWaiters(0); // signal all threads
+ releaseWaiters(1);
}
/**
@@ -632,17 +674,7 @@ public class Phaser {
* @return the phase number, or a negative value if terminated
*/
public final int getPhase() {
- return phaseOf(getReconciledState());
- }
-
- /**
- * Returns {@code true} if the current phase number equals the given phase.
- *
- * @param phase the phase
- * @return {@code true} if the current phase number equals the given phase
- */
- public final boolean hasPhase(int phase) {
- return phaseOf(getReconciledState()) == phase;
+ return (int)((parent == null? state : reconcileState()) >>> PHASE_SHIFT);
}
/**
@@ -651,17 +683,17 @@ public class Phaser {
* @return the number of parties
*/
public int getRegisteredParties() {
- return partiesOf(state);
+ return partiesOf(parent == null? state : reconcileState());
}
/**
- * 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);
+ return arrivedOf(parent == null? state : reconcileState());
}
/**
@@ -671,13 +703,13 @@ public class Phaser {
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(state);
+ return unarrivedOf(parent == null? state : reconcileState());
}
/**
- * Returns the parent of this phaser, or null if none.
+ * Returns the parent of this phaser, or {@code null} if none.
*
- * @return the parent of this phaser, or null if none
+ * @return the parent of this phaser, or {@code null} if none
*/
public Phaser getParent() {
return parent;
@@ -699,34 +731,36 @@ public class Phaser {
* @return {@code true} if this barrier has been terminated
*/
public boolean isTerminated() {
- return getPhase() < 0;
+ return (parent == null? state : reconcileState()) < 0;
}
/**
- * 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 {@code isTerminated} will
- * return true.
+ * Overridable method to perform an action upon impending phase
+ * advance, and to control termination. This method is invoked
+ * upon arrival of the party tripping the barrier (when all other
+ * waiting parties are dormant). If this method returns {@code
+ * true}, then, rather than advance the phase number, this barrier
+ * will be set to a final termination state, and subsequent calls
+ * to {@link #isTerminated} will return true. Any (unchecked)
+ * Exception or Error thrown by an invocation of this method is
+ * propagated to the party attempting to trip the barrier, in
+ * which case no advance occurs.
+ *
+ * The arguments to this method provide the state of the phaser
+ * prevailing for the current transition. The 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.
*
- *
The default version returns true when the number of
+ *
The default version returns {@code true} when the number of
* registered parties is zero. Normally, overrides that arrange
* termination for other reasons should also preserve this
* property.
*
- *
You may override this method to perform an action with side
- * effects visible to participating tasks, but it is in general
- * only sensible to do so in designs where all parties register
- * before any arrive, and all {@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
- * invocation of this method is in progress, thus postponing the
- * transition until those parties also arrive, re-triggering this
- * method.
- *
* @param phase the phase number on entering the barrier
* @param registeredParties the current number of registered parties
* @return {@code true} if this barrier should terminate
@@ -745,14 +779,113 @@ public class Phaser {
* @return a string identifying this barrier, as well as its state
*/
public String toString() {
- long s = getReconciledState();
+ long s = reconcileState();
return super.toString() +
"[phase = " + phaseOf(s) +
" parties = " + partiesOf(s) +
" arrived = " + arrivedOf(s) + "]";
}
- // methods for waiting
+ /**
+ * Removes and signals threads from queue for phase
+ */
+ private void releaseWaiters(int phase) {
+ AtomicReference head = queueFor(phase);
+ QNode q;
+ int p;
+ while ((q = head.get()) != null &&
+ ((p = q.phase) == phase ||
+ (int)(root.state >>> PHASE_SHIFT) != p)) {
+ if (head.compareAndSet(q, q.next))
+ q.signal();
+ }
+ }
+
+ /**
+ * Tries to enqueue given node in the appropriate wait queue.
+ *
+ * @return true if successful
+ */
+ private boolean tryEnqueue(int phase, QNode node) {
+ releaseWaiters(phase-1); // ensure old queue clean
+ AtomicReference head = queueFor(phase);
+ QNode q = head.get();
+ return ((q == null || q.phase == phase) &&
+ (int)(root.state >>> PHASE_SHIFT) == phase &&
+ head.compareAndSet(node.next = q, node));
+ }
+
+ /** 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 continuing to try to
+ * block. 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 nonnull, 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
+ Phaser par = parent;
+ boolean queued = false;
+ int spins = SPINS_PER_ARRIVAL;
+ int lastUnarrived = -1; // to increase spins upon change
+ long s;
+ int p;
+ while ((p = (int)((s = current.state) >>> PHASE_SHIFT)) == phase) {
+ int unarrived = (int)(s & UNARRIVED_MASK);
+ if (unarrived != lastUnarrived) {
+ if ((lastUnarrived = unarrived) < NCPU)
+ spins += SPINS_PER_ARRIVAL;
+ }
+ else if (unarrived == 0 && par != null) {
+ current = par; // if all arrived, use parent
+ par = par.parent;
+ }
+ else if (spins > 0)
+ --spins;
+ else if (node == null)
+ node = new QNode(this, phase, false, false, 0L);
+ else if (node.isReleasable())
+ break;
+ else if (!queued)
+ queued = tryEnqueue(phase, node);
+ else {
+ try {
+ ForkJoinPool.managedBlock(node);
+ } catch (InterruptedException ie) {
+ node.wasInterrupted = true;
+ }
+ }
+ }
+ if (node != null) {
+ if (node.thread != null)
+ node.thread = null;
+ if (!node.interruptible && node.wasInterrupted)
+ Thread.currentThread().interrupt();
+ }
+ if (p == phase)
+ p = (int)(reconcileState() >>> PHASE_SHIFT);
+ if (p != phase)
+ releaseWaiters(phase);
+ return p;
+ }
/**
* Wait nodes for Treiber stack representing wait queue
@@ -760,45 +893,62 @@ public class Phaser {
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;
+ 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 startTime, long nanos) {
+ boolean timed, long nanos) {
this.phaser = phaser;
this.phase = phase;
- this.timed = timed;
this.interruptible = interruptible;
- this.startTime = startTime;
this.nanos = nanos;
+ this.timed = timed;
+ this.lastTime = timed? System.nanoTime() : 0L;
thread = Thread.currentThread();
}
+
public boolean isReleasable() {
- return (thread == null ||
- phaser.getPhase() != phase ||
- (interruptible && wasInterrupted) ||
- (timed && (nanos - (System.nanoTime() - startTime)) <= 0));
+ 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;
+ }
+ }
+ if (t != null)
+ return false;
+ thread = null;
+ }
+ return true;
}
+
public boolean block() {
- if (Thread.interrupted()) {
- wasInterrupted = true;
- if (interruptible)
- return true;
- }
- if (!timed)
+ if (isReleasable())
+ return true;
+ else if (!timed)
LockSupport.park(this);
- else {
- long waitTime = nanos - (System.nanoTime() - startTime);
- if (waitTime <= 0)
- return true;
- LockSupport.parkNanos(this, waitTime);
- }
+ else if (nanos > 0)
+ LockSupport.parkNanos(this, nanos);
return isReleasable();
}
+
void signal() {
Thread t = thread;
if (t != null) {
@@ -806,140 +956,45 @@ public class Phaser {
LockSupport.unpark(t);
}
}
- boolean doWait() {
- if (thread != null) {
- try {
- ForkJoinPool.managedBlock(this, false);
- } catch (InterruptedException ie) {
- }
- }
- return wasInterrupted;
- }
-
}
- /**
- * Removes and signals waiting threads from wait queue.
- */
- private void releaseWaiters(int phase) {
- AtomicReference head = queueFor(phase);
- QNode q;
- while ((q = head.get()) != null) {
- if (head.compareAndSet(q, q.next))
- q.signal();
- }
- }
+ // Unsafe mechanics
- /**
- * Tries to enqueue given node in the appropriate wait queue.
- *
- * @return true if successful
- */
- private boolean tryEnqueue(QNode node) {
- AtomicReference head = queueFor(node.phase);
- return head.compareAndSet(node.next = head.get(), node);
- }
-
- /**
- * Enqueues node and waits unless aborted or signalled.
- *
- * @return current phase
- */
- private int untimedWait(int phase) {
- QNode node = null;
- boolean queued = false;
- boolean interrupted = false;
- int p;
- while ((p = getPhase()) == phase) {
- if (Thread.interrupted())
- interrupted = true;
- else if (node == null)
- node = new QNode(this, phase, false, false, 0, 0);
- else if (!queued)
- queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
- }
- if (node != null)
- node.thread = null;
- releaseWaiters(phase);
- if (interrupted)
- Thread.currentThread().interrupt();
- return p;
- }
+ private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+ private static final long stateOffset =
+ objectFieldOffset("state", Phaser.class);
- /**
- * Interruptible version
- * @return current phase
- */
- private int interruptibleWait(int phase) throws InterruptedException {
- QNode node = null;
- boolean queued = false;
- boolean interrupted = false;
- int p;
- while ((p = getPhase()) == phase && !interrupted) {
- if (Thread.interrupted())
- interrupted = true;
- else if (node == null)
- node = new QNode(this, phase, true, false, 0, 0);
- else if (!queued)
- queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
- }
- if (node != null)
- node.thread = null;
- if (p != phase || (p = getPhase()) != phase)
- releaseWaiters(phase);
- if (interrupted)
- throw new InterruptedException();
- return p;
+ 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;
+ }
}
/**
- * Timeout version.
- * @return current phase
+ * 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 int timedWait(int phase, long nanos)
- throws InterruptedException, TimeoutException {
- long startTime = System.nanoTime();
- QNode node = null;
- boolean queued = false;
- boolean interrupted = false;
- int p;
- while ((p = getPhase()) == phase && !interrupted) {
- if (Thread.interrupted())
- interrupted = true;
- else if (nanos - (System.nanoTime() - startTime) <= 0)
- break;
- else if (node == null)
- node = new QNode(this, phase, true, true, startTime, nanos);
- else if (!queued)
- queued = tryEnqueue(node);
- else
- interrupted = node.doWait();
- }
- if (node != null)
- node.thread = null;
- if (p != phase || (p = getPhase()) != phase)
- releaseWaiters(phase);
- if (interrupted)
- throw new InterruptedException();
- if (p == phase)
- throw new TimeoutException();
- return p;
- }
-
- // Unsafe mechanics for jsr166y 3rd party package.
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() {
+ (new java.security
+ .PrivilegedExceptionAction() {
public sun.misc.Unsafe run() throws Exception {
- return getUnsafeByReflection();
+ 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",
@@ -947,31 +1002,4 @@ public class Phaser {
}
}
}
-
- private static sun.misc.Unsafe getUnsafeByReflection()
- throws NoSuchFieldException, IllegalAccessException {
- java.lang.reflect.Field f =
- sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (sun.misc.Unsafe) f.get(null);
- }
-
- private static long fieldOffset(String fieldName, Class klazz) {
- try {
- return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
- } catch (NoSuchFieldException e) {
- // Convert Exception to Error
- NoSuchFieldError error = new NoSuchFieldError(fieldName);
- error.initCause(e);
- throw error;
- }
- }
-
- private static final sun.misc.Unsafe UNSAFE = getUnsafe();
- static final long stateOffset =
- fieldOffset("state", Phaser.class);
-
- final boolean casState(long cmp, long val) {
- return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
- }
}