--- jsr166/src/jsr166y/Phaser.java 2009/07/23 23:07:57 1.18 +++ jsr166/src/jsr166y/Phaser.java 2009/08/23 20:12:24 1.36 @@ -7,10 +7,9 @@ package jsr166y; import java.util.concurrent.*; -import java.util.concurrent.atomic.*; + +import java.util.concurrent.atomic.AtomicReference; import java.util.concurrent.locks.LockSupport; -import sun.misc.Unsafe; -import java.lang.reflect.*; /** * A reusable synchronization barrier, similar in functionality to a @@ -20,53 +19,58 @@ import java.lang.reflect.*; * *
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 +150,9 @@ 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) { @@ -172,7 +182,7 @@ 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. * @@ -250,7 +260,7 @@ 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; @@ -301,16 +311,16 @@ 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 @@ -322,7 +332,7 @@ 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. @@ -342,7 +352,7 @@ 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. @@ -369,7 +379,7 @@ public class Phaser { /** * Adds a new unarrived party to this phaser. * - * @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 */ @@ -381,7 +391,7 @@ public class Phaser { * Adds the given number of new unarrived parties to this phaser. * * @param parties the number of parties required to trip barrier - * @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 */ @@ -418,8 +428,7 @@ public class Phaser { * Arrives at the barrier, but does not wait for others. (You can * in turn wait for others via {@link #awaitAdvance}). * - * @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 */ @@ -464,14 +473,14 @@ 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 + * @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 */ @@ -521,11 +530,13 @@ 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 + * @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 */ @@ -534,12 +545,16 @@ 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. - * - * @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) @@ -555,13 +570,17 @@ 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. - * - * @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) @@ -578,12 +597,21 @@ 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. - * - * @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 */ @@ -637,16 +665,6 @@ 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 @@ -656,8 +674,8 @@ public class Phaser { } /** - * 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 */ @@ -676,9 +694,9 @@ 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; @@ -707,26 +725,22 @@ 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 @@ -931,49 +945,52 @@ 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()); + } + } } }