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package jsr166y; |
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import java.util.concurrent.*; |
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import java.util.concurrent.atomic.*; |
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import java.util.concurrent.atomic.AtomicReference; |
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import java.util.concurrent.locks.LockSupport; |
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import sun.misc.Unsafe; |
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import java.lang.reflect.*; |
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/** |
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* A reusable synchronization barrier, similar in functionality to a |
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* zero, and advancing when all parties reach the barrier (wrapping |
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* around to zero after reaching {@code Integer.MAX_VALUE}). |
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* |
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* <li> Like a CyclicBarrier, a Phaser may be repeatedly awaited. |
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* Method {@code arriveAndAwaitAdvance} has effect analogous to |
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* {@code CyclicBarrier.await}. However, Phasers separate two |
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* aspects of coordination, that may also be invoked independently: |
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* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly |
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* awaited. Method {@link #arriveAndAwaitAdvance} has effect |
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* analogous to {@link java.util.concurrent.CyclicBarrier#await |
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* CyclicBarrier.await}. However, phasers separate two aspects of |
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* coordination, that may also be invoked independently: |
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* |
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* <ul> |
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* |
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* <li> Arriving at a barrier. Methods {@code arrive} and |
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* {@code arriveAndDeregister} do not block, but return |
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* <li> Arriving at a barrier. Methods {@link #arrive} and |
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* {@link #arriveAndDeregister} do not block, but return |
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* the phase value current upon entry to the method. |
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* |
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* <li> Awaiting others. Method {@code awaitAdvance} requires an |
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* <li> Awaiting others. Method {@link #awaitAdvance} requires an |
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* argument indicating the entry phase, and returns when the |
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* barrier advances to a new phase. |
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* </ul> |
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* |
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* <li> Barrier actions, performed by the task triggering a phase |
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* advance while others may be waiting, are arranged by overriding |
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* method {@code onAdvance}, that also controls termination. |
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* method {@link #onAdvance}, that also controls termination. |
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* Overriding this method may be used to similar but more flexible |
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* effect as providing a barrier action to a CyclicBarrier. |
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* effect as providing a barrier action to a {@code CyclicBarrier}. |
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* |
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* <li> Phasers may enter a <em>termination</em> state in which all |
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* actions immediately return without updating phaser state or waiting |
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* for advance, and indicating (via a negative phase value) that |
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* execution is complete. Termination is triggered by executing the |
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* overridable {@code onAdvance} method that is invoked each time the |
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* barrier is about to be tripped. When a Phaser is controlling an |
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* barrier is about to be tripped. When a phaser is controlling an |
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* action with a fixed number of iterations, it is often convenient to |
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* override this method to cause termination when the current phase |
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* number reaches a threshold. Method {@code forceTermination} is also |
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* number reaches a threshold. Method {@link #forceTermination} is also |
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* available to abruptly release waiting threads and allow them to |
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* terminate. |
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* |
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* |
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* <li> By default, {@code awaitAdvance} continues to wait even if |
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* the waiting thread is interrupted. And unlike the case in |
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* CyclicBarriers, exceptions encountered while tasks wait |
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* {@code CyclicBarrier}, exceptions encountered while tasks wait |
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* interruptibly or with timeout do not change the state of the |
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* barrier. If necessary, you can perform any associated recovery |
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* within handlers of those exceptions, often after invoking |
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* |
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* <p><b>Sample usages:</b> |
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* |
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* <p>A Phaser may be used instead of a {@code CountDownLatch} to control |
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* a one-shot action serving a variable number of parties. The typical |
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* idiom is for the method setting this up to first register, then |
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* start the actions, then deregister, as in: |
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* <p>A {@code Phaser} may be used instead of a {@code CountDownLatch} |
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* to control a one-shot action serving a variable number of |
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* parties. The typical idiom is for the method setting this up to |
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* first register, then start the actions, then deregister, as in: |
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* |
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* <pre> {@code |
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* void runTasks(List<Runnable> list) { |
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* phaser.arriveAndDeregister(); // deregister self, don't wait |
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* }}</pre> |
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* |
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* <p> To create a set of tasks using a tree of Phasers, |
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* <p>To create a set of tasks using a tree of phasers, |
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* you could use code of the following form, assuming a |
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* Task class with a constructor accepting a Phaser that |
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* Task class with a constructor accepting a phaser that |
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* it registers for upon construction: |
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* <pre> {@code |
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* void build(Task[] actions, int lo, int hi, Phaser b) { |
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private static final int phaseMask = 0x7fffffff; |
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private static int unarrivedOf(long s) { |
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return (int)(s & ushortMask); |
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return (int) (s & ushortMask); |
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} |
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private static int partiesOf(long s) { |
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private final Phaser parent; |
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/** |
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* The root of Phaser tree. Equals this if not in a tree. Used to |
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* The root of phaser tree. Equals this if not in a tree. Used to |
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* support faster state push-down. |
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*/ |
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private final Phaser root; |
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private final AtomicReference<QNode> oddQ = new AtomicReference<QNode>(); |
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private AtomicReference<QNode> queueFor(int phase) { |
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return (phase & 1) == 0? evenQ : oddQ; |
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return ((phase & 1) == 0) ? evenQ : oddQ; |
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} |
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/** |
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* root if necessary. |
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*/ |
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private long getReconciledState() { |
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return parent == null? state : reconcileState(); |
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return (parent == null) ? state : reconcileState(); |
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} |
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/** |
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} |
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/** |
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* Creates a new Phaser without any initially registered parties, |
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* Creates a new phaser without any initially registered parties, |
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* initial phase number 0, and no parent. Any thread using this |
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* Phaser will need to first register for it. |
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* phaser will need to first register for it. |
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*/ |
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public Phaser() { |
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this(null); |
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} |
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/** |
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* Creates a new Phaser with the given numbers of registered |
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* Creates a new phaser with the given numbers of registered |
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* unarrived parties, initial phase number 0, and no parent. |
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* |
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* @param parties the number of parties required to trip barrier |
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} |
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/** |
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* Creates a new Phaser with the given parent, without any |
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* Creates a new phaser with the given parent, without any |
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* initially registered parties. If parent is non-null this phaser |
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* is registered with the parent and its initial phase number is |
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* the same as that of parent phaser. |
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} |
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/** |
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* Creates a new Phaser with the given parent and numbers of |
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* Creates a new phaser with the given parent and numbers of |
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* registered unarrived parties. If parent is non-null, this phaser |
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* is registered with the parent and its initial phase number is |
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* the same as that of parent phaser. |
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if (par == null) { // directly trip |
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if (casState |
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(s, |
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trippedStateFor(onAdvance(phase, parties)? -1 : |
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trippedStateFor(onAdvance(phase, parties) ? -1 : |
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((phase + 1) & phaseMask), parties))) { |
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releaseWaiters(phase); |
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break; |
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if (unarrived == 0) { |
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if (casState |
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(s, |
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trippedStateFor(onAdvance(phase, parties)? -1 : |
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trippedStateFor(onAdvance(phase, parties) ? -1 : |
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((phase + 1) & phaseMask), parties))) { |
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releaseWaiters(phase); |
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break; |
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* @throws InterruptedException if thread interrupted while waiting |
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* @throws TimeoutException if timed out while waiting |
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*/ |
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public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit) |
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public int awaitAdvanceInterruptibly(int phase, |
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long timeout, TimeUnit unit) |
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throws InterruptedException, TimeoutException { |
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if (phase < 0) |
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return phase; |
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} |
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/** |
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* Returns the parent of this phaser, or null if none. |
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* Returns the parent of this phaser, or {@code null} if none. |
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* |
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* @return the parent of this phaser, or null if none |
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* @return the parent of this phaser, or {@code null} if none |
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*/ |
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public Phaser getParent() { |
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return parent; |
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* Overridable method to perform an action upon phase advance, and |
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* to control termination. This method is invoked whenever the |
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* barrier is tripped (and thus all other waiting parties are |
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* dormant). If it returns true, then, rather than advance the |
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* phase number, this barrier will be set to a final termination |
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* state, and subsequent calls to {@code isTerminated} will |
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* return true. |
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* dormant). If it returns {@code true}, then, rather than advance |
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* the phase number, this barrier will be set to a final |
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* termination state, and subsequent calls to {@link #isTerminated} |
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* will return true. |
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* |
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* <p> The default version returns true when the number of |
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* <p>The default version returns {@code true} when the number of |
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* registered parties is zero. Normally, overrides that arrange |
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* termination for other reasons should also preserve this |
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* property. |
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* |
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* <p> You may override this method to perform an action with side |
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* <p>You may override this method to perform an action with side |
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* effects visible to participating tasks, but it is in general |
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* only sensible to do so in designs where all parties register |
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* before any arrive, and all {@code awaitAdvance} at each phase. |
723 |
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* before any arrive, and all {@link #awaitAdvance} at each phase. |
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* Otherwise, you cannot ensure lack of interference. In |
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* particular, this method may be invoked more than once per |
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* transition if other parties successfully register while the |
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return p; |
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} |
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// Temporary Unsafe mechanics for preliminary release |
934 |
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private static Unsafe getUnsafe() throws Throwable { |
935 |
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try { |
936 |
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return Unsafe.getUnsafe(); |
937 |
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} catch (SecurityException se) { |
938 |
< |
try { |
939 |
< |
return java.security.AccessController.doPrivileged |
940 |
< |
(new java.security.PrivilegedExceptionAction<Unsafe>() { |
941 |
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public Unsafe run() throws Exception { |
942 |
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return getUnsafePrivileged(); |
943 |
< |
}}); |
944 |
< |
} catch (java.security.PrivilegedActionException e) { |
945 |
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throw e.getCause(); |
946 |
< |
} |
947 |
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} |
948 |
< |
} |
934 |
> |
// Unsafe mechanics |
935 |
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|
936 |
< |
private static Unsafe getUnsafePrivileged() |
937 |
< |
throws NoSuchFieldException, IllegalAccessException { |
938 |
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Field f = Unsafe.class.getDeclaredField("theUnsafe"); |
953 |
< |
f.setAccessible(true); |
954 |
< |
return (Unsafe) f.get(null); |
955 |
< |
} |
936 |
> |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
937 |
> |
private static final long stateOffset = |
938 |
> |
objectFieldOffset("state", Phaser.class); |
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|
940 |
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private static long fieldOffset(String fieldName) |
941 |
< |
throws NoSuchFieldException { |
959 |
< |
return UNSAFE.objectFieldOffset |
960 |
< |
(Phaser.class.getDeclaredField(fieldName)); |
940 |
> |
private final boolean casState(long cmp, long val) { |
941 |
> |
return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val); |
942 |
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} |
943 |
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|
944 |
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static final Unsafe UNSAFE; |
964 |
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static final long stateOffset; |
965 |
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|
966 |
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static { |
944 |
> |
private static long objectFieldOffset(String field, Class<?> klazz) { |
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try { |
946 |
< |
UNSAFE = getUnsafe(); |
947 |
< |
stateOffset = fieldOffset("state"); |
948 |
< |
} catch (Throwable e) { |
949 |
< |
throw new RuntimeException("Could not initialize intrinsics", e); |
946 |
> |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
947 |
> |
} catch (NoSuchFieldException e) { |
948 |
> |
// Convert Exception to corresponding Error |
949 |
> |
NoSuchFieldError error = new NoSuchFieldError(field); |
950 |
> |
error.initCause(e); |
951 |
> |
throw error; |
952 |
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} |
953 |
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} |
954 |
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|
955 |
< |
final boolean casState(long cmp, long val) { |
956 |
< |
return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val); |
955 |
> |
/** |
956 |
> |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
957 |
> |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
958 |
> |
* into a jdk. |
959 |
> |
* |
960 |
> |
* @return a sun.misc.Unsafe |
961 |
> |
*/ |
962 |
> |
private static sun.misc.Unsafe getUnsafe() { |
963 |
> |
try { |
964 |
> |
return sun.misc.Unsafe.getUnsafe(); |
965 |
> |
} catch (SecurityException se) { |
966 |
> |
try { |
967 |
> |
return java.security.AccessController.doPrivileged |
968 |
> |
(new java.security |
969 |
> |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
970 |
> |
public sun.misc.Unsafe run() throws Exception { |
971 |
> |
java.lang.reflect.Field f = sun.misc |
972 |
> |
.Unsafe.class.getDeclaredField("theUnsafe"); |
973 |
> |
f.setAccessible(true); |
974 |
> |
return (sun.misc.Unsafe) f.get(null); |
975 |
> |
}}); |
976 |
> |
} catch (java.security.PrivilegedActionException e) { |
977 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
978 |
> |
e.getCause()); |
979 |
> |
} |
980 |
> |
} |
981 |
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} |
982 |
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} |