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) {
* return phase >= iterations || registeredParties == 0;
* }
* };
* phaser.register();
- * for (Runnable r : list) {
+ * for (Runnable task : tasks) {
* phaser.register();
* new Thread() {
* public void run() {
* do {
- * r.run();
+ * task.run();
* phaser.arriveAndAwaitAdvance();
* } while(!phaser.isTerminated();
* }
@@ -140,9 +137,9 @@ import java.lang.reflect.*;
* phaser.arriveAndDeregister(); // deregister self, don't wait
* }}
*
- * 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 + * Task class with a constructor accepting a phaser that * it registers for upon construction: *
{@code
* void build(Task[] actions, int lo, int hi, Phaser b) {
@@ -172,9 +169,12 @@ import java.lang.reflect.*;
*
* 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.
+ *
+ * @since 1.7
+ * @author Doug Lea
*/
public class Phaser {
/*
@@ -208,15 +208,15 @@ public class Phaser {
private static final int phaseMask = 0x7fffffff;
private static int unarrivedOf(long s) {
- return (int)(s & ushortMask);
+ return (int) (s & ushortMask);
}
private static int partiesOf(long s) {
- return ((int)s) >>> 16;
+ return ((int) s) >>> 16;
}
private static int phaseOf(long s) {
- return (int)(s >>> 32);
+ return (int) (s >>> 32);
}
private static int arrivedOf(long s) {
@@ -224,13 +224,13 @@ public class Phaser {
}
private static long stateFor(int phase, int parties, int unarrived) {
- return ((((long)phase) << 32) | (((long)parties) << 16) |
- (long)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;
+ long lp = (long) parties;
+ return (((long) phase) << 32) | (lp << 16) | lp;
}
/**
@@ -247,7 +247,7 @@ public class Phaser {
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;
@@ -263,7 +263,7 @@ public class Phaser {
private final AtomicReference oddQ = new AtomicReference();
private AtomicReference queueFor(int phase) {
- return (phase & 1) == 0? evenQ : oddQ;
+ return ((phase & 1) == 0) ? evenQ : oddQ;
}
/**
@@ -271,7 +271,7 @@ public class Phaser {
* root if necessary.
*/
private long getReconciledState() {
- return parent == null? state : reconcileState();
+ return (parent == null) ? state : reconcileState();
}
/**
@@ -298,16 +298,16 @@ public class Phaser {
}
/**
- * 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);
}
/**
- * Creates a new Phaser with the given numbers of registered
+ * Creates a new phaser with the given numbers of registered
* unarrived parties, initial phase number 0, and no parent.
*
* @param parties the number of parties required to trip barrier
@@ -319,7 +319,7 @@ 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.
@@ -339,7 +339,7 @@ public class Phaser {
}
/**
- * Creates a new Phaser with the given parent and numbers of
+ * Creates a new phaser with the given parent and numbers 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.
@@ -438,7 +438,7 @@ public class Phaser {
if (par == null) { // directly trip
if (casState
(s,
- trippedStateFor(onAdvance(phase, parties)? -1 :
+ trippedStateFor(onAdvance(phase, parties) ? -1 :
((phase + 1) & phaseMask), parties))) {
releaseWaiters(phase);
break;
@@ -461,11 +461,12 @@ public class Phaser {
}
/**
- * 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.
*
* @return the current barrier phase number upon entry to
* this method, or a negative value if terminated
@@ -499,7 +500,7 @@ public class Phaser {
if (unarrived == 0) {
if (casState
(s,
- trippedStateFor(onAdvance(phase, parties)? -1 :
+ trippedStateFor(onAdvance(phase, parties) ? -1 :
((phase + 1) & phaseMask), parties))) {
releaseWaiters(phase);
break;
@@ -518,9 +519,11 @@ public class Phaser {
/**
* 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 awaitAdvance
+ * method. If instead you need to deregister upon arrival use
+ * {@code arriveAndDeregister}.
*
* @return the phase on entry to this method
* @throws IllegalStateException if not terminated and the number
@@ -531,12 +534,15 @@ 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.
+ * 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 the phase on entry to this method
- * @return the phase on exit from this method
+ * @return the current barrier phase number upon exit of
+ * this method, or a negative value if terminated or
+ * argument is negative
*/
public int awaitAdvance(int phase) {
if (phase < 0)
@@ -552,13 +558,16 @@ 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, 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
+ * @return the current barrier phase number upon exit of
+ * this method, or a negative value if terminated or
+ * argument is negative
* @throws InterruptedException if thread interrupted while waiting
*/
public int awaitAdvanceInterruptibly(int phase)
@@ -575,16 +584,25 @@ public class Phaser {
}
/**
- * 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.
+ * 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 the phase on entry to this method
- * @return the phase on exit from this method
+ * @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 current barrier phase number upon exit of
+ * this method, 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;
@@ -633,16 +651,6 @@ public class Phaser {
}
/**
- * 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;
- }
-
- /**
* Returns the number of parties registered at this barrier.
*
* @return the number of parties
@@ -672,9 +680,9 @@ public class Phaser {
}
/**
- * 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;
@@ -703,26 +711,22 @@ public class Phaser {
* 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.
+ * dormant). If it 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.
*
- * 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
+ *
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.
+ * 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.
*
* @param phase the phase number on entering the barrier
* @param registeredParties the current number of registered parties
@@ -927,49 +931,52 @@ public class Phaser {
return p;
}
- // Temporary Unsafe mechanics for preliminary release
- private static Unsafe getUnsafe() throws Throwable {
- try {
- return Unsafe.getUnsafe();
- } catch (SecurityException se) {
- try {
- return java.security.AccessController.doPrivileged
- (new java.security.PrivilegedExceptionAction() {
- public Unsafe run() throws Exception {
- return getUnsafePrivileged();
- }});
- } catch (java.security.PrivilegedActionException e) {
- throw e.getCause();
- }
- }
- }
+ // Unsafe mechanics
- private static Unsafe getUnsafePrivileged()
- throws NoSuchFieldException, IllegalAccessException {
- Field f = Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (Unsafe) f.get(null);
- }
+ private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+ private static final long stateOffset =
+ objectFieldOffset("state", Phaser.class);
- private static long fieldOffset(String fieldName)
- throws NoSuchFieldException {
- return _unsafe.objectFieldOffset
- (Phaser.class.getDeclaredField(fieldName));
+ private final boolean casState(long cmp, long val) {
+ return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
}
- static final Unsafe _unsafe;
- static final long stateOffset;
-
- static {
+ private static long objectFieldOffset(String field, Class klazz) {
try {
- _unsafe = getUnsafe();
- stateOffset = fieldOffset("state");
- } catch (Throwable e) {
- throw new RuntimeException("Could not initialize intrinsics", e);
+ return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+ } catch (NoSuchFieldException e) {
+ // Convert Exception to corresponding Error
+ NoSuchFieldError error = new NoSuchFieldError(field);
+ error.initCause(e);
+ throw error;
}
}
- final boolean casState(long cmp, long val) {
- return _unsafe.compareAndSwapLong(this, stateOffset, cmp, val);
+ /**
+ * 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 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());
+ }
+ }
}
}