Packaging the new FJ pool into Akka

akka-actor/src/main/java/akka/jsr166y/ForkJoinWorkerThread.java

@@ -0,0 +1,119 @@
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package akka.jsr166y;
+
+/**
+ * A thread managed by a {@link ForkJoinPool}, which executes
+ * {@link ForkJoinTask}s.
+ * This class is subclassable solely for the sake of adding
+ * functionality -- there are no overridable methods dealing with
+ * scheduling or execution.  However, you can override initialization
+ * and termination methods surrounding the main task processing loop.
+ * If you do create such a subclass, you will also need to supply a
+ * custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to use it
+ * in a {@code ForkJoinPool}.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public class ForkJoinWorkerThread extends Thread {
+    /*
+     * ForkJoinWorkerThreads are managed by ForkJoinPools and perform
+     * ForkJoinTasks. For explanation, see the internal documentation
+     * of class ForkJoinPool.
+     */
+
+    final ForkJoinPool.WorkQueue workQueue; // Work-stealing mechanics
+    final ForkJoinPool pool;                // the pool this thread works in
+
+    /**
+     * Creates a ForkJoinWorkerThread operating in the given pool.
+     *
+     * @param pool the pool this thread works in
+     * @throws NullPointerException if pool is null
+     */
+    protected ForkJoinWorkerThread(ForkJoinPool pool) {
+        super(pool.nextWorkerName());
+        setDaemon(true);
+        Thread.UncaughtExceptionHandler ueh = pool.ueh;
+        if (ueh != null)
+            setUncaughtExceptionHandler(ueh);
+        this.pool = pool;
+        this.workQueue = new ForkJoinPool.WorkQueue(this, pool.localMode);
+        pool.registerWorker(this);
+    }
+
+    /**
+     * Returns the pool hosting this thread.
+     *
+     * @return the pool
+     */
+    public ForkJoinPool getPool() {
+        return pool;
+    }
+
+    /**
+     * Returns the index number of this thread in its pool.  The
+     * returned value ranges from zero to the maximum number of
+     * threads (minus one) that have ever been created in the pool.
+     * This method may be useful for applications that track status or
+     * collect results per-worker rather than per-task.
+     *
+     * @return the index number
+     */
+    public int getPoolIndex() {
+        return workQueue.poolIndex;
+    }
+
+    /**
+     * Initializes internal state after construction but before
+     * processing any tasks. If you override this method, you must
+     * invoke {@code super.onStart()} at the beginning of the method.
+     * Initialization requires care: Most fields must have legal
+     * default values, to ensure that attempted accesses from other
+     * threads work correctly even before this thread starts
+     * processing tasks.
+     */
+    protected void onStart() {
+    }
+
+    /**
+     * Performs cleanup associated with termination of this worker
+     * thread.  If you override this method, you must invoke
+     * {@code super.onTermination} at the end of the overridden method.
+     *
+     * @param exception the exception causing this thread to abort due
+     * to an unrecoverable error, or {@code null} if completed normally
+     */
+    protected void onTermination(Throwable exception) {
+    }
+
+    /**
+     * This method is required to be public, but should never be
+     * called explicitly. It performs the main run loop to execute
+     * {@link ForkJoinTask}s.
+     */
+    public void run() {
+        Throwable exception = null;
+        try {
+            onStart();
+            pool.runWorker(this);
+        } catch (Throwable ex) {
+            exception = ex;
+        } finally {
+            try {
+                onTermination(exception);
+            } catch (Throwable ex) {
+                if (exception == null)
+                    exception = ex;
+            } finally {
+                pool.deregisterWorker(this, exception);
+            }
+        }
+    }
+}
+

akka-actor/src/main/java/akka/jsr166y/RecursiveAction.java

@@ -0,0 +1,164 @@
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package akka.jsr166y;
+
+/**
+ * A recursive resultless {@link ForkJoinTask}.  This class
+ * establishes conventions to parameterize resultless actions as
+ * {@code Void} {@code ForkJoinTask}s. Because {@code null} is the
+ * only valid value of type {@code Void}, methods such as {@code join}
+ * always return {@code null} upon completion.
+ *
+ * <p><b>Sample Usages.</b> Here is a simple but complete ForkJoin
+ * sort that sorts a given {@code long[]} array:
+ *
+ *  <pre> {@code
+ * static class SortTask extends RecursiveAction {
+ *   final long[] array; final int lo, hi;
+ *   SortTask(long[] array, int lo, int hi) {
+ *     this.array = array; this.lo = lo; this.hi = hi;
+ *   }
+ *   SortTask(long[] array) { this(array, 0, array.length); }
+ *   protected void compute() {
+ *     if (hi - lo < THRESHOLD)
+ *       sortSequentially(lo, hi);
+ *     else {
+ *       int mid = (lo + hi) >>> 1;
+ *       invokeAll(new SortTask(array, lo, mid),
+ *                 new SortTask(array, mid, hi));
+ *       merge(lo, mid, hi);
+ *     }
+ *   }
+ *   // implementation details follow:
+ *   final static int THRESHOLD = 1000;
+ *   void sortSequentially(int lo, int hi) {
+ *     Arrays.sort(array, lo, hi);
+ *   }
+ *   void merge(int lo, int mid, int hi) {
+ *     long[] buf = Arrays.copyOfRange(array, lo, mid);
+ *     for (int i = 0, j = lo, k = mid; i < buf.length; j++)
+ *       array[j] = (k == hi || buf[i] < array[k]) ?
+ *         buf[i++] : array[k++];
+ *   }
+ * }}</pre>
+ *
+ * You could then sort {@code anArray} by creating {@code new
+ * SortTask(anArray)} and invoking it in a ForkJoinPool.  As a more
+ * concrete simple example, the following task increments each element
+ * of an array:
+ *  <pre> {@code
+ * class IncrementTask extends RecursiveAction {
+ *   final long[] array; final int lo, hi;
+ *   IncrementTask(long[] array, int lo, int hi) {
+ *     this.array = array; this.lo = lo; this.hi = hi;
+ *   }
+ *   protected void compute() {
+ *     if (hi - lo < THRESHOLD) {
+ *       for (int i = lo; i < hi; ++i)
+ *         array[i]++;
+ *     }
+ *     else {
+ *       int mid = (lo + hi) >>> 1;
+ *       invokeAll(new IncrementTask(array, lo, mid),
+ *                 new IncrementTask(array, mid, hi));
+ *     }
+ *   }
+ * }}</pre>
+ *
+ * <p>The following example illustrates some refinements and idioms
+ * that may lead to better performance: RecursiveActions need not be
+ * fully recursive, so long as they maintain the basic
+ * divide-and-conquer approach. Here is a class that sums the squares
+ * of each element of a double array, by subdividing out only the
+ * right-hand-sides of repeated divisions by two, and keeping track of
+ * them with a chain of {@code next} references. It uses a dynamic
+ * threshold based on method {@code getSurplusQueuedTaskCount}, but
+ * counterbalances potential excess partitioning by directly
+ * performing leaf actions on unstolen tasks rather than further
+ * subdividing.
+ *
+ *  <pre> {@code
+ * double sumOfSquares(ForkJoinPool pool, double[] array) {
+ *   int n = array.length;
+ *   Applyer a = new Applyer(array, 0, n, null);
+ *   pool.invoke(a);
+ *   return a.result;
+ * }
+ *
+ * class Applyer extends RecursiveAction {
+ *   final double[] array;
+ *   final int lo, hi;
+ *   double result;
+ *   Applyer next; // keeps track of right-hand-side tasks
+ *   Applyer(double[] array, int lo, int hi, Applyer next) {
+ *     this.array = array; this.lo = lo; this.hi = hi;
+ *     this.next = next;
+ *   }
+ *
+ *   double atLeaf(int l, int h) {
+ *     double sum = 0;
+ *     for (int i = l; i < h; ++i) // perform leftmost base step
+ *       sum += array[i] * array[i];
+ *     return sum;
+ *   }
+ *
+ *   protected void compute() {
+ *     int l = lo;
+ *     int h = hi;
+ *     Applyer right = null;
+ *     while (h - l > 1 && getSurplusQueuedTaskCount() <= 3) {
+ *        int mid = (l + h) >>> 1;
+ *        right = new Applyer(array, mid, h, right);
+ *        right.fork();
+ *        h = mid;
+ *     }
+ *     double sum = atLeaf(l, h);
+ *     while (right != null) {
+ *        if (right.tryUnfork()) // directly calculate if not stolen
+ *          sum += right.atLeaf(right.lo, right.hi);
+ *       else {
+ *          right.join();
+ *          sum += right.result;
+ *        }
+ *        right = right.next;
+ *      }
+ *     result = sum;
+ *   }
+ * }}</pre>
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public abstract class RecursiveAction extends ForkJoinTask<Void> {
+    private static final long serialVersionUID = 5232453952276485070L;
+
+    /**
+     * The main computation performed by this task.
+     */
+    protected abstract void compute();
+
+    /**
+     * Always returns {@code null}.
+     *
+     * @return {@code null} always
+     */
+    public final Void getRawResult() { return null; }
+
+    /**
+     * Requires null completion value.
+     */
+    protected final void setRawResult(Void mustBeNull) { }
+
+    /**
+     * Implements execution conventions for RecursiveActions.
+     */
+    protected final boolean exec() {
+        compute();
+        return true;
+    }
+
+}

akka-actor/src/main/java/akka/jsr166y/RecursiveTask.java

@@ -0,0 +1,68 @@
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package akka.jsr166y;
+
+/**
+ * A recursive result-bearing {@link ForkJoinTask}.
+ *
+ * <p>For a classic example, here is a task computing Fibonacci numbers:
+ *
+ *  <pre> {@code
+ * class Fibonacci extends RecursiveTask<Integer> {
+ *   final int n;
+ *   Fibonacci(int n) { this.n = n; }
+ *   Integer compute() {
+ *     if (n <= 1)
+ *        return n;
+ *     Fibonacci f1 = new Fibonacci(n - 1);
+ *     f1.fork();
+ *     Fibonacci f2 = new Fibonacci(n - 2);
+ *     return f2.compute() + f1.join();
+ *   }
+ * }}</pre>
+ *
+ * However, besides being a dumb way to compute Fibonacci functions
+ * (there is a simple fast linear algorithm that you'd use in
+ * practice), this is likely to perform poorly because the smallest
+ * subtasks are too small to be worthwhile splitting up. Instead, as
+ * is the case for nearly all fork/join applications, you'd pick some
+ * minimum granularity size (for example 10 here) for which you always
+ * sequentially solve rather than subdividing.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
+    private static final long serialVersionUID = 5232453952276485270L;
+
+    /**
+     * The result of the computation.
+     */
+    V result;
+
+    /**
+     * The main computation performed by this task.
+     */
+    protected abstract V compute();
+
+    public final V getRawResult() {
+        return result;
+    }
+
+    protected final void setRawResult(V value) {
+        result = value;
+    }
+
+    /**
+     * Implements execution conventions for RecursiveTask.
+     */
+    protected final boolean exec() {
+        result = compute();
+        return true;
+    }
+
+}

akka-actor/src/main/scala/akka/dispatch/ThreadPoolBuilder.scala

@@ -8,6 +8,7 @@ import java.util.Collection
 import java.util.concurrent.atomic.AtomicLong
 import akka.util.Duration
 import java.util.concurrent._
+import akka.jsr166y._
 
 object ThreadPoolConfig {
   type QueueFactory = () ⇒ BlockingQueue[Runnable]
@@ -160,9 +161,15 @@ object MonitorableThreadFactory {
 case class MonitorableThreadFactory(name: String,
                                     daemonic: Boolean,
                                     exceptionHandler: Thread.UncaughtExceptionHandler = MonitorableThreadFactory.doNothing)
-  extends ThreadFactory {
+  extends ThreadFactory with ForkJoinPool.ForkJoinWorkerThreadFactory {
   protected val counter = new AtomicLong
 
+  def newThread(pool: ForkJoinPool): ForkJoinWorkerThread = {
+    val t = ForkJoinPool.defaultForkJoinWorkerThreadFactory.newThread(pool)
+    t.setDaemon(daemonic)
+    t
+  }
+
   def newThread(runnable: Runnable) = {
     val t = new Thread(runnable, name + counter.incrementAndGet())
     t.setUncaughtExceptionHandler(exceptionHandler)