--- jsr166/src/jsr166y/ForkJoinTask.java	2010/08/11 18:45:12	1.53
+++ jsr166/src/jsr166y/ForkJoinTask.java	2011/03/04 13:29:39	1.76
@@ -6,15 +6,26 @@
 
 package jsr166y;
 
-import java.util.concurrent.*;
-
 import java.io.Serializable;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.RandomAccess;
 import java.util.Map;
-import java.util.WeakHashMap;
+import java.lang.ref.WeakReference;
+import java.lang.ref.ReferenceQueue;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.RunnableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.locks.ReentrantLock;
+import java.lang.reflect.Constructor;
 
 /**
  * Abstract base class for tasks that run within a {@link ForkJoinPool}.
@@ -28,10 +39,10 @@ import java.util.WeakHashMap;
  * start other subtasks.  As indicated by the name of this class,
  * many programs using {@code ForkJoinTask} employ only methods
  * {@link #fork} and {@link #join}, or derivatives such as {@link
- * #invokeAll}.  However, this class also provides a number of other
- * methods that can come into play in advanced usages, as well as
- * extension mechanics that allow support of new forms of fork/join
- * processing.
+ * #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
+ * provides a number of other methods that can come into play in
+ * advanced usages, as well as extension mechanics that allow
+ * support of new forms of fork/join processing.
  *
  * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
  * The efficiency of {@code ForkJoinTask}s stems from a set of
@@ -58,7 +69,11 @@ import java.util.WeakHashMap;
  * rethrown to callers attempting to join them. These exceptions may
  * additionally include {@link RejectedExecutionException} stemming
  * from internal resource exhaustion, such as failure to allocate
- * internal task queues.
+ * internal task queues. Rethrown exceptions behave in the same way as
+ * regular exceptions, but, when possible, contain stack traces (as
+ * displayed for example using {@code ex.printStackTrace()}) of both
+ * the thread that initiated the computation as well as the thread
+ * actually encountering the exception; minimally only the latter.
  *
  * <p>The primary method for awaiting completion and extracting
  * results of a task is {@link #join}, but there are several variants:
@@ -100,7 +115,17 @@ import java.util.WeakHashMap;
  * ForkJoinTasks (as may be determined using method {@link
  * #inForkJoinPool}).  Attempts to invoke them in other contexts
  * result in exceptions or errors, possibly including
- * ClassCastException.
+ * {@code ClassCastException}.
+ *
+ * <p>Method {@link #join} and its variants are appropriate for use
+ * only when completion dependencies are acyclic; that is, the
+ * parallel computation can be described as a directed acyclic graph
+ * (DAG). Otherwise, executions may encounter a form of deadlock as
+ * tasks cyclically wait for each other.  However, this framework
+ * supports other methods and techniques (for example the use of
+ * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
+ * may be of use in constructing custom subclasses for problems that
+ * are not statically structured as DAGs.
  *
  * <p>Most base support methods are {@code final}, to prevent
  * overriding of implementations that are intrinsically tied to the
@@ -116,9 +141,10 @@ import java.util.WeakHashMap;
  * computation. Large tasks should be split into smaller subtasks,
  * usually via recursive decomposition. As a very rough rule of thumb,
  * a task should perform more than 100 and less than 10000 basic
- * computational steps. If tasks are too big, then parallelism cannot
- * improve throughput. If too small, then memory and internal task
- * maintenance overhead may overwhelm processing.
+ * computational steps, and should avoid indefinite looping. If tasks
+ * are too big, then parallelism cannot improve throughput. If too
+ * small, then memory and internal task maintenance overhead may
+ * overwhelm processing.
  *
  * <p>This class provides {@code adapt} methods for {@link Runnable}
  * and {@link Callable}, that may be of use when mixing execution of
@@ -144,8 +170,7 @@ public abstract class ForkJoinTask<V> im
      * status maintenance (2) execution and awaiting completion (3)
      * user-level methods that additionally report results. This is
      * sometimes hard to see because this file orders exported methods
-     * in a way that flows well in javadocs. In particular, most
-     * join mechanics are in method quietlyJoin, below.
+     * in a way that flows well in javadocs.
      */
 
     /*
@@ -153,7 +178,7 @@ public abstract class ForkJoinTask<V> im
      * single int to minimize footprint and to ensure atomicity (via
      * CAS).  Status is initially zero, and takes on nonnegative
      * values until completed, upon which status holds value
-     * COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
+     * NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
      * waits by other threads have the SIGNAL bit set.  Completion of
      * a stolen task with SIGNAL set awakens any waiters via
      * notifyAll. Even though suboptimal for some purposes, we use
@@ -167,107 +192,381 @@ public abstract class ForkJoinTask<V> im
 
     /** The run status of this task */
     volatile int status; // accessed directly by pool and workers
-
     private static final int NORMAL      = -1;
     private static final int CANCELLED   = -2;
     private static final int EXCEPTIONAL = -3;
     private static final int SIGNAL      =  1;
 
     /**
-     * Table of exceptions thrown by tasks, to enable reporting by
-     * callers. Because exceptions are rare, we don't directly keep
-     * them with task objects, but instead use a weak ref table.  Note
-     * that cancellation exceptions don't appear in the table, but are
-     * instead recorded as status values.
-     * TODO: Use ConcurrentReferenceHashMap
-     */
-    static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
-        Collections.synchronizedMap
-        (new WeakHashMap<ForkJoinTask<?>, Throwable>());
-
-    // Maintaining completion status
-
-    /**
      * Marks completion and wakes up threads waiting to join this task,
      * also clearing signal request bits.
      *
      * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
+     * @return completion status on exit
      */
-    private void setCompletion(int completion) {
-        int s;
-        while ((s = status) >= 0) {
+    private int setCompletion(int completion) {
+        for (int s;;) {
+            if ((s = status) < 0)
+                return s;
             if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
                 if (s != 0)
                     synchronized (this) { notifyAll(); }
-                break;
+                return completion;
             }
         }
     }
 
     /**
-     * Record exception and set exceptional completion
-     * @return status on exit
-     */
-    private void setExceptionalCompletion(Throwable rex) {
-        exceptionMap.put(this, rex);
-        setCompletion(EXCEPTIONAL);
-    }
-
-    /**
-     * Blocks a worker thread until completion. Called only by pool.
+     * Tries to block a worker thread until completed or timed out.
+     * Uses Object.wait time argument conventions.
+     * May fail on contention or interrupt.
+     *
+     * @param millis if > 0, wait time.
      */
-    final void internalAwaitDone() {
-        int s;         // the odd construction reduces lock bias effects
-        while ((s = status) >= 0) {
-            try {
-                synchronized(this) {
-                    if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
-                        wait();
+    final void tryAwaitDone(long millis) {
+        int s;
+        try {
+            if (((s = status) > 0 ||
+                 (s == 0 &&
+                  UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
+                status > 0) {
+                synchronized (this) {
+                    if (status > 0)
+                        wait(millis);
                 }
-            } catch (InterruptedException ie) {
-                cancelIfTerminating();
             }
+        } catch (InterruptedException ie) {
+            // caller must check termination
         }
     }
 
     /**
      * Blocks a non-worker-thread until completion.
+     * @return status upon completion
      */
-    private void externalAwaitDone() {
+    private int externalAwaitDone() {
         int s;
-        while ((s = status) >= 0) {
-            synchronized(this) {
-                if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
-                    boolean interrupted = false;
-                    while (status >= 0) {
+        if ((s = status) >= 0) {
+            boolean interrupted = false;
+            synchronized (this) {
+                while ((s = status) >= 0) {
+                    if (s == 0)
+                        UNSAFE.compareAndSwapInt(this, statusOffset,
+                                                 0, SIGNAL);
+                    else {
                         try {
                             wait();
                         } catch (InterruptedException ie) {
                             interrupted = true;
                         }
                     }
-                    if (interrupted)
-                        Thread.currentThread().interrupt();
-                    break;
                 }
             }
+            if (interrupted)
+                Thread.currentThread().interrupt();
         }
+        return s;
     }
 
     /**
-     * Unless done, calls exec and records status if completed, but
-     * doesn't wait for completion otherwise. Primary execution method
-     * for ForkJoinWorkerThread.
+     * Blocks a non-worker-thread until completion or interruption or timeout.
      */
-    final void quietlyExec() {
-        try {
-            if (status < 0 || !exec())
+    private int externalInterruptibleAwaitDone(long millis)
+        throws InterruptedException {
+        int s;
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        if ((s = status) >= 0) {
+            synchronized (this) {
+                while ((s = status) >= 0) {
+                    if (s == 0)
+                        UNSAFE.compareAndSwapInt(this, statusOffset,
+                                                 0, SIGNAL);
+                    else {
+                        wait(millis);
+                        if (millis > 0L)
+                            break;
+                    }
+                }
+            }
+        }
+        return s;
+    }
+
+    /**
+     * Primary execution method for stolen tasks. Unless done, calls
+     * exec and records status if completed, but doesn't wait for
+     * completion otherwise.
+     */
+    final void doExec() {
+        if (status >= 0) {
+            boolean completed;
+            try {
+                completed = exec();
+            } catch (Throwable rex) {
+                setExceptionalCompletion(rex);
                 return;
+            }
+            if (completed)
+                setCompletion(NORMAL); // must be outside try block
+        }
+    }
+
+    /**
+     * Primary mechanics for join, get, quietlyJoin.
+     * @return status upon completion
+     */
+    private int doJoin() {
+        Thread t; ForkJoinWorkerThread w; int s; boolean completed;
+        if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
+            if ((s = status) < 0)
+                return s;
+            if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
+                try {
+                    completed = exec();
+                } catch (Throwable rex) {
+                    return setExceptionalCompletion(rex);
+                }
+                if (completed)
+                    return setCompletion(NORMAL);
+            }
+            return w.joinTask(this);
+        }
+        else
+            return externalAwaitDone();
+    }
+
+    /**
+     * Primary mechanics for invoke, quietlyInvoke.
+     * @return status upon completion
+     */
+    private int doInvoke() {
+        int s; boolean completed;
+        if ((s = status) < 0)
+            return s;
+        try {
+            completed = exec();
         } catch (Throwable rex) {
-            setExceptionalCompletion(rex);
-            return;
+            return setExceptionalCompletion(rex);
+        }
+        if (completed)
+            return setCompletion(NORMAL);
+        else
+            return doJoin();
+    }
+
+    // Exception table support
+
+    /**
+     * Table of exceptions thrown by tasks, to enable reporting by
+     * callers. Because exceptions are rare, we don't directly keep
+     * them with task objects, but instead use a weak ref table.  Note
+     * that cancellation exceptions don't appear in the table, but are
+     * instead recorded as status values.
+     *
+     * Note: These statics are initialized below in static block.
+     */
+    private static final ExceptionNode[] exceptionTable;
+    private static final ReentrantLock exceptionTableLock;
+    private static final ReferenceQueue<Object> exceptionTableRefQueue;
+
+    /**
+     * Fixed capacity for exceptionTable.
+     */
+    private static final int EXCEPTION_MAP_CAPACITY = 32;
+
+    /**
+     * Key-value nodes for exception table.  The chained hash table
+     * uses identity comparisons, full locking, and weak references
+     * for keys. The table has a fixed capacity because it only
+     * maintains task exceptions long enough for joiners to access
+     * them, so should never become very large for sustained
+     * periods. However, since we do not know when the last joiner
+     * completes, we must use weak references and expunge them. We do
+     * so on each operation (hence full locking). Also, some thread in
+     * any ForkJoinPool will call helpExpungeStaleExceptions when its
+     * pool becomes isQuiescent.
+     */
+    static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
+        final Throwable ex;
+        ExceptionNode next;
+        final long thrower;  // use id not ref to avoid weak cycles
+        ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
+            super(task, exceptionTableRefQueue);
+            this.ex = ex;
+            this.next = next;
+            this.thrower = Thread.currentThread().getId();
+        }
+    }
+
+    /**
+     * Records exception and sets exceptional completion.
+     *
+     * @return status on exit
+     */
+    private int setExceptionalCompletion(Throwable ex) {
+        int h = System.identityHashCode(this);
+        final ReentrantLock lock = exceptionTableLock;
+        lock.lock();
+        try {
+            expungeStaleExceptions();
+            ExceptionNode[] t = exceptionTable;
+            int i = h & (t.length - 1);
+            for (ExceptionNode e = t[i]; ; e = e.next) {
+                if (e == null) {
+                    t[i] = new ExceptionNode(this, ex, t[i]);
+                    break;
+                }
+                if (e.get() == this) // already present
+                    break;
+            }
+        } finally {
+            lock.unlock();
+        }
+        return setCompletion(EXCEPTIONAL);
+    }
+
+    /**
+     * Removes exception node and clears status
+     */
+    private void clearExceptionalCompletion() {
+        int h = System.identityHashCode(this);
+        final ReentrantLock lock = exceptionTableLock;
+        lock.lock();
+        try {
+            ExceptionNode[] t = exceptionTable;
+            int i = h & (t.length - 1);
+            ExceptionNode e = t[i];
+            ExceptionNode pred = null;
+            while (e != null) {
+                ExceptionNode next = e.next;
+                if (e.get() == this) {
+                    if (pred == null)
+                        t[i] = next;
+                    else
+                        pred.next = next;
+                    break;
+                }
+                pred = e;
+                e = next;
+            }
+            expungeStaleExceptions();
+            status = 0;
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    /**
+     * Returns a rethrowable exception for the given task, if
+     * available. To provide accurate stack traces, if the exception
+     * was not thrown by the current thread, we try to create a new
+     * exception of the same type as the one thrown, but with the
+     * recorded exception as its cause. If there is no such
+     * constructor, we instead try to use a no-arg constructor,
+     * followed by initCause, to the same effect. If none of these
+     * apply, or any fail due to other exceptions, we return the
+     * recorded exception, which is still correct, although it may
+     * contain a misleading stack trace.
+     *
+     * @return the exception, or null if none
+     */
+    private Throwable getThrowableException() {
+        if (status != EXCEPTIONAL)
+            return null;
+        int h = System.identityHashCode(this);
+        ExceptionNode e;
+        final ReentrantLock lock = exceptionTableLock;
+        lock.lock();
+        try {
+            expungeStaleExceptions();
+            ExceptionNode[] t = exceptionTable;
+            e = t[h & (t.length - 1)];
+            while (e != null && e.get() != this)
+                e = e.next;
+        } finally {
+            lock.unlock();
+        }
+        Throwable ex;
+        if (e == null || (ex = e.ex) == null)
+            return null;
+        if (e.thrower != Thread.currentThread().getId()) {
+            Class ec = ex.getClass();
+            try {
+                Constructor<?> noArgCtor = null;
+                Constructor<?>[] cs = ec.getConstructors();// public ctors only
+                for (int i = 0; i < cs.length; ++i) {
+                    Constructor<?> c = cs[i];
+                    Class<?>[] ps = c.getParameterTypes();
+                    if (ps.length == 0)
+                        noArgCtor = c;
+                    else if (ps.length == 1 && ps[0] == Throwable.class)
+                        return (Throwable)(c.newInstance(ex));
+                }
+                if (noArgCtor != null) {
+                    Throwable wx = (Throwable)(noArgCtor.newInstance());
+                    wx.initCause(ex);
+                    return wx;
+                }
+            } catch (Exception ignore) {
+            }
         }
-        setCompletion(NORMAL); // must be outside try block
+        return ex;
+    }
+
+    /**
+     * Poll stale refs and remove them. Call only while holding lock.
+     */
+    private static void expungeStaleExceptions() {
+        for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
+            if (x instanceof ExceptionNode) {
+                ForkJoinTask<?> key = ((ExceptionNode)x).get();
+                ExceptionNode[] t = exceptionTable;
+                int i = System.identityHashCode(key) & (t.length - 1);
+                ExceptionNode e = t[i];
+                ExceptionNode pred = null;
+                while (e != null) {
+                    ExceptionNode next = e.next;
+                    if (e == x) {
+                        if (pred == null)
+                            t[i] = next;
+                        else
+                            pred.next = next;
+                        break;
+                    }
+                    pred = e;
+                    e = next;
+                }
+            }
+        }
+    }
+
+    /**
+     * If lock is available, poll stale refs and remove them.
+     * Called from ForkJoinPool when pools become quiescent.
+     */
+    static final void helpExpungeStaleExceptions() {
+        final ReentrantLock lock = exceptionTableLock;
+        if (lock.tryLock()) {
+            try {
+                expungeStaleExceptions();
+            } finally {
+                lock.unlock();
+            }
+        }
+    }
+
+    /**
+     * Report the result of invoke or join; called only upon
+     * non-normal return of internal versions.
+     */
+    private V reportResult() {
+        int s; Throwable ex;
+        if ((s = status) == CANCELLED)
+            throw new CancellationException();
+        if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
+            UNSAFE.throwException(ex);
+        return getRawResult();
     }
 
     // public methods
@@ -283,7 +582,7 @@ public abstract class ForkJoinTask<V> im
      * #isDone} returning {@code true}.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -297,47 +596,53 @@ public abstract class ForkJoinTask<V> im
     }
 
     /**
-     * Returns the result of the computation when it {@link #isDone is done}.
-     * This method differs from {@link #get()} in that
+     * Returns the result of the computation when it {@link #isDone is
+     * done}.  This method differs from {@link #get()} in that
      * abnormal completion results in {@code RuntimeException} or
-     * {@code Error}, not {@code ExecutionException}.
+     * {@code Error}, not {@code ExecutionException}, and that
+     * interrupts of the calling thread do <em>not</em> cause the
+     * method to abruptly return by throwing {@code
+     * InterruptedException}.
      *
      * @return the computed result
      */
     public final V join() {
-        quietlyJoin();
-        Throwable ex;
-        if (status < NORMAL && (ex = getException()) != null)
-            UNSAFE.throwException(ex);
-        return getRawResult();
+        if (doJoin() != NORMAL)
+            return reportResult();
+        else
+            return getRawResult();
     }
 
     /**
      * Commences performing this task, awaits its completion if
-     * necessary, and return its result, or throws an (unchecked)
-     * exception if the underlying computation did so.
+     * necessary, and returns its result, or throws an (unchecked)
+     * {@code RuntimeException} or {@code Error} if the underlying
+     * computation did so.
      *
      * @return the computed result
      */
     public final V invoke() {
-        quietlyInvoke();
-        Throwable ex;
-        if (status < NORMAL && (ex = getException()) != null)
-            UNSAFE.throwException(ex);
-        return getRawResult();
+        if (doInvoke() != NORMAL)
+            return reportResult();
+        else
+            return getRawResult();
     }
 
     /**
      * Forks the given tasks, returning when {@code isDone} holds for
      * each task or an (unchecked) exception is encountered, in which
-     * case the exception is rethrown.  If either task encounters an
-     * exception, the other one may be, but is not guaranteed to be,
-     * cancelled.  If both tasks throw an exception, then this method
-     * throws one of them.  The individual status of each task may be
-     * checked using {@link #getException()} and related methods.
+     * case the exception is rethrown. If more than one task
+     * encounters an exception, then this method throws any one of
+     * these exceptions. If any task encounters an exception, the
+     * other may be cancelled. However, the execution status of
+     * individual tasks is not guaranteed upon exceptional return. The
+     * status of each task may be obtained using {@link
+     * #getException()} and related methods to check if they have been
+     * cancelled, completed normally or exceptionally, or left
+     * unprocessed.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -355,15 +660,17 @@ public abstract class ForkJoinTask<V> im
     /**
      * Forks the given tasks, returning when {@code isDone} holds for
      * each task or an (unchecked) exception is encountered, in which
-     * case the exception is rethrown. If any task encounters an
-     * exception, others may be, but are not guaranteed to be,
-     * cancelled.  If more than one task encounters an exception, then
-     * this method throws any one of these exceptions.  The individual
-     * status of each task may be checked using {@link #getException()}
-     * and related methods.
+     * case the exception is rethrown. If more than one task
+     * encounters an exception, then this method throws any one of
+     * these exceptions. If any task encounters an exception, others
+     * may be cancelled. However, the execution status of individual
+     * tasks is not guaranteed upon exceptional return. The status of
+     * each task may be obtained using {@link #getException()} and
+     * related methods to check if they have been cancelled, completed
+     * normally or exceptionally, or left unprocessed.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -382,22 +689,16 @@ public abstract class ForkJoinTask<V> im
             }
             else if (i != 0)
                 t.fork();
-            else {
-                t.quietlyInvoke();
-                if (ex == null && t.status < NORMAL)
-                    ex = t.getException();
-            }
+            else if (t.doInvoke() < NORMAL && ex == null)
+                ex = t.getException();
         }
         for (int i = 1; i <= last; ++i) {
             ForkJoinTask<?> t = tasks[i];
             if (t != null) {
                 if (ex != null)
                     t.cancel(false);
-                else {
-                    t.quietlyJoin();
-                    if (ex == null && t.status < NORMAL)
-                        ex = t.getException();
-                }
+                else if (t.doJoin() < NORMAL && ex == null)
+                    ex = t.getException();
             }
         }
         if (ex != null)
@@ -407,17 +708,18 @@ public abstract class ForkJoinTask<V> im
     /**
      * Forks all tasks in the specified collection, returning when
      * {@code isDone} holds for each task or an (unchecked) exception
-     * is encountered.  If any task encounters an exception, others
-     * may be, but are not guaranteed to be, cancelled.  If more than
-     * one task encounters an exception, then this method throws any
-     * one of these exceptions.  The individual status of each task
-     * may be checked using {@link #getException()} and related
-     * methods.  The behavior of this operation is undefined if the
-     * specified collection is modified while the operation is in
-     * progress.
+     * is encountered, in which case the exception is rethrown. If
+     * more than one task encounters an exception, then this method
+     * throws any one of these exceptions. If any task encounters an
+     * exception, others may be cancelled. However, the execution
+     * status of individual tasks is not guaranteed upon exceptional
+     * return. The status of each task may be obtained using {@link
+     * #getException()} and related methods to check if they have been
+     * cancelled, completed normally or exceptionally, or left
+     * unprocessed.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -444,22 +746,16 @@ public abstract class ForkJoinTask<V> im
             }
             else if (i != 0)
                 t.fork();
-            else {
-                t.quietlyInvoke();
-                if (ex == null && t.status < NORMAL)
-                    ex = t.getException();
-            }
+            else if (t.doInvoke() < NORMAL && ex == null)
+                ex = t.getException();
         }
         for (int i = 1; i <= last; ++i) {
             ForkJoinTask<?> t = ts.get(i);
             if (t != null) {
                 if (ex != null)
                     t.cancel(false);
-                else {
-                    t.quietlyJoin();
-                    if (ex == null && t.status < NORMAL)
-                        ex = t.getException();
-                }
+                else if (t.doJoin() < NORMAL && ex == null)
+                    ex = t.getException();
             }
         }
         if (ex != null)
@@ -469,31 +765,33 @@ public abstract class ForkJoinTask<V> im
 
     /**
      * Attempts to cancel execution of this task. This attempt will
-     * fail if the task has already completed, has already been
-     * cancelled, or could not be cancelled for some other reason. If
-     * successful, and this task has not started when cancel is
-     * called, execution of this task is suppressed, {@link
-     * #isCancelled} will report true, and {@link #join} will result
-     * in a {@code CancellationException} being thrown.
+     * fail if the task has already completed or could not be
+     * cancelled for some other reason. If successful, and this task
+     * has not started when {@code cancel} is called, execution of
+     * this task is suppressed. After this method returns
+     * successfully, unless there is an intervening call to {@link
+     * #reinitialize}, subsequent calls to {@link #isCancelled},
+     * {@link #isDone}, and {@code cancel} will return {@code true}
+     * and calls to {@link #join} and related methods will result in
+     * {@code CancellationException}.
      *
      * <p>This method may be overridden in subclasses, but if so, must
-     * still ensure that these minimal properties hold. In particular,
-     * the {@code cancel} method itself must not throw exceptions.
+     * still ensure that these properties hold. In particular, the
+     * {@code cancel} method itself must not throw exceptions.
      *
      * <p>This method is designed to be invoked by <em>other</em>
      * tasks. To terminate the current task, you can just return or
      * throw an unchecked exception from its computation method, or
      * invoke {@link #completeExceptionally}.
      *
-     * @param mayInterruptIfRunning this value is ignored in the
-     * default implementation because tasks are not
-     * cancelled via interruption
+     * @param mayInterruptIfRunning this value has no effect in the
+     * default implementation because interrupts are not used to
+     * control cancellation.
      *
      * @return {@code true} if this task is now cancelled
      */
     public boolean cancel(boolean mayInterruptIfRunning) {
-        setCompletion(CANCELLED);
-        return status == CANCELLED;
+        return setCompletion(CANCELLED) == CANCELLED;
     }
 
     /**
@@ -509,20 +807,6 @@ public abstract class ForkJoinTask<V> im
         }
     }
 
-    /**
-     * Cancels ignoring exceptions if worker is terminating
-     */
-    final void cancelIfTerminating() {
-        Thread t = Thread.currentThread();
-        if ((t instanceof ForkJoinWorkerThread) &&
-            ((ForkJoinWorkerThread) t).isTerminating()) {
-            try {
-                cancel(false);
-            } catch (Throwable ignore) {
-            }
-        }
-    }
-
     public final boolean isDone() {
         return status < 0;
     }
@@ -562,7 +846,7 @@ public abstract class ForkJoinTask<V> im
         int s = status;
         return ((s >= NORMAL)    ? null :
                 (s == CANCELLED) ? new CancellationException() :
-                exceptionMap.get(this));
+                getThrowableException());
     }
 
     /**
@@ -587,13 +871,14 @@ public abstract class ForkJoinTask<V> im
 
     /**
      * Completes this task, and if not already aborted or cancelled,
-     * returning a {@code null} result upon {@code join} and related
-     * operations. This method may be used to provide results for
-     * asynchronous tasks, or to provide alternative handling for
-     * tasks that would not otherwise complete normally. Its use in
-     * other situations is discouraged. This method is
-     * overridable, but overridden versions must invoke {@code super}
-     * implementation to maintain guarantees.
+     * returning the given value as the result of subsequent
+     * invocations of {@code join} and related operations. This method
+     * may be used to provide results for asynchronous tasks, or to
+     * provide alternative handling for tasks that would not otherwise
+     * complete normally. Its use in other situations is
+     * discouraged. This method is overridable, but overridden
+     * versions must invoke {@code super} implementation to maintain
+     * guarantees.
      *
      * @param value the result value for this task
      */
@@ -607,91 +892,77 @@ public abstract class ForkJoinTask<V> im
         setCompletion(NORMAL);
     }
 
+    /**
+     * Waits if necessary for the computation to complete, and then
+     * retrieves its result.
+     *
+     * @return the computed result
+     * @throws CancellationException if the computation was cancelled
+     * @throws ExecutionException if the computation threw an
+     * exception
+     * @throws InterruptedException if the current thread is not a
+     * member of a ForkJoinPool and was interrupted while waiting
+     */
     public final V get() throws InterruptedException, ExecutionException {
-        quietlyJoin();
-        if (Thread.interrupted())
-            throw new InterruptedException();
-        int s = status;
-        if (s < NORMAL) {
-            Throwable ex;
-            if (s == CANCELLED)
-                throw new CancellationException();
-            if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
-                throw new ExecutionException(ex);
-        }
+        int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
+            doJoin() : externalInterruptibleAwaitDone(0L);
+        Throwable ex;
+        if (s == CANCELLED)
+            throw new CancellationException();
+        if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
+            throw new ExecutionException(ex);
         return getRawResult();
     }
 
+    /**
+     * Waits if necessary for at most the given time for the computation
+     * to complete, and then retrieves its result, if available.
+     *
+     * @param timeout the maximum time to wait
+     * @param unit the time unit of the timeout argument
+     * @return the computed result
+     * @throws CancellationException if the computation was cancelled
+     * @throws ExecutionException if the computation threw an
+     * exception
+     * @throws InterruptedException if the current thread is not a
+     * member of a ForkJoinPool and was interrupted while waiting
+     * @throws TimeoutException if the wait timed out
+     */
     public final V get(long timeout, TimeUnit unit)
         throws InterruptedException, ExecutionException, TimeoutException {
         Thread t = Thread.currentThread();
-        ForkJoinPool pool;
         if (t instanceof ForkJoinWorkerThread) {
             ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
-            if (status >= 0 && w.unpushTask(this))
-                quietlyExec();
-            pool = w.pool;
-        }
-        else
-            pool = null;
-        /*
-         * Timed wait loop intermixes cases for FJ (pool != null) and
-         * non FJ threads. For FJ, decrement pool count but don't try
-         * for replacement; increment count on completion. For non-FJ,
-         * deal with interrupts. This is messy, but a little less so
-         * than is splitting the FJ and nonFJ cases.
-         */
-        boolean interrupted = false;
-        boolean dec = false; // true if pool count decremented
-        for (;;) {
-            if (Thread.interrupted() && pool == null) {
-                interrupted = true;
-                break;
-            }
-            int s = status;
-            if (s < 0)
-                break;
-            if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
-                long startTime = System.nanoTime();
-                long nanos = unit.toNanos(timeout);
-                long nt; // wait time
-                while (status >= 0 &&
-                       (nt = nanos - (System.nanoTime() - startTime)) > 0) {
-                    if (pool != null && !dec)
-                        dec = pool.tryDecrementRunningCount();
-                    else {
-                        long ms = nt / 1000000;
-                        int ns = (int) (nt % 1000000);
-                        try {
-                            synchronized(this) {
-                                if (status >= 0)
-                                    wait(ms, ns);
-                            }
-                        } catch (InterruptedException ie) {
-                            if (pool != null)
-                                cancelIfTerminating();
-                            else {
-                                interrupted = true;
-                                break;
-                            }
-                        }
+            long nanos = unit.toNanos(timeout);
+            if (status >= 0) {
+                boolean completed = false;
+                if (w.unpushTask(this)) {
+                    try {
+                        completed = exec();
+                    } catch (Throwable rex) {
+                        setExceptionalCompletion(rex);
                     }
                 }
-                break;
+                if (completed)
+                    setCompletion(NORMAL);
+                else if (status >= 0 && nanos > 0)
+                    w.pool.timedAwaitJoin(this, nanos);
             }
         }
-        if (pool != null && dec)
-            pool.incrementRunningCount();
-        if (interrupted)
-            throw new InterruptedException();
-        int es = status;
-        if (es != NORMAL) {
+        else {
+            long millis = unit.toMillis(timeout);
+            if (millis > 0)
+                externalInterruptibleAwaitDone(millis);
+        }
+        int s = status;
+        if (s != NORMAL) {
             Throwable ex;
-            if (es == CANCELLED)
+            if (s == CANCELLED)
                 throw new CancellationException();
-            if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+            if (s != EXCEPTIONAL)
+                throw new TimeoutException();
+            if ((ex = getThrowableException()) != null)
                 throw new ExecutionException(ex);
-            throw new TimeoutException();
         }
         return getRawResult();
     }
@@ -703,51 +974,16 @@ public abstract class ForkJoinTask<V> im
      * known to have aborted.
      */
     public final void quietlyJoin() {
-        Thread t;
-        if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
-            ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
-            if (status >= 0) {
-                if (w.unpushTask(this)) {
-                    boolean completed;
-                    try {
-                        completed = exec();
-                    } catch (Throwable rex) {
-                        setExceptionalCompletion(rex);
-                        return;
-                    }
-                    if (completed) {
-                        setCompletion(NORMAL);
-                        return;
-                    }
-                }
-                w.joinTask(this);
-            }
-        }
-        else
-            externalAwaitDone();
+        doJoin();
     }
 
     /**
      * Commences performing this task and awaits its completion if
      * necessary, without returning its result or throwing its
-     * exception. This method may be useful when processing
-     * collections of tasks when some have been cancelled or otherwise
-     * known to have aborted.
+     * exception.
      */
     public final void quietlyInvoke() {
-        if (status >= 0) {
-            boolean completed;
-            try {
-                completed = exec();
-            } catch (Throwable rex) {
-                setExceptionalCompletion(rex);
-                return;
-            }
-            if (completed)
-                setCompletion(NORMAL);
-            else
-                quietlyJoin();
-        }
+        doInvoke();
     }
 
     /**
@@ -758,7 +994,7 @@ public abstract class ForkJoinTask<V> im
      * processed.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -777,11 +1013,18 @@ public abstract class ForkJoinTask<V> im
      * under any other usage conditions are not guaranteed.
      * This method may be useful when executing
      * pre-constructed trees of subtasks in loops.
+     *
+     * <p>Upon completion of this method, {@code isDone()} reports
+     * {@code false}, and {@code getException()} reports {@code
+     * null}. However, the value returned by {@code getRawResult} is
+     * unaffected. To clear this value, you can invoke {@code
+     * setRawResult(null)}.
      */
     public void reinitialize() {
         if (status == EXCEPTIONAL)
-            exceptionMap.remove(this);
-        status = 0;
+            clearExceptionalCompletion();
+        else
+            status = 0;
     }
 
     /**
@@ -798,11 +1041,12 @@ public abstract class ForkJoinTask<V> im
     }
 
     /**
-     * Returns {@code true} if the current thread is executing as a
-     * ForkJoinPool computation.
+     * Returns {@code true} if the current thread is a {@link
+     * ForkJoinWorkerThread} executing as a ForkJoinPool computation.
      *
-     * @return {@code true} if the current thread is executing as a
-     * ForkJoinPool computation, or false otherwise
+     * @return {@code true} if the current thread is a {@link
+     * ForkJoinWorkerThread} executing as a ForkJoinPool computation,
+     * or {@code false} otherwise
      */
     public static boolean inForkJoinPool() {
         return Thread.currentThread() instanceof ForkJoinWorkerThread;
@@ -817,7 +1061,7 @@ public abstract class ForkJoinTask<V> im
      * were not, stolen.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -836,7 +1080,7 @@ public abstract class ForkJoinTask<V> im
      * fork other tasks.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -859,7 +1103,7 @@ public abstract class ForkJoinTask<V> im
      * exceeded.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -917,7 +1161,7 @@ public abstract class ForkJoinTask<V> im
      * otherwise.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -936,7 +1180,7 @@ public abstract class ForkJoinTask<V> im
      * be useful otherwise.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -959,7 +1203,7 @@ public abstract class ForkJoinTask<V> im
      * otherwise.
      *
      * <p>This method may be invoked only from within {@code
-     * ForkJoinTask} computations (as may be determined using method
+     * ForkJoinPool} computations (as may be determined using method
      * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
      * result in exceptions or errors, possibly including {@code
      * ClassCastException}.
@@ -1069,7 +1313,7 @@ public abstract class ForkJoinTask<V> im
     private static final long serialVersionUID = -7721805057305804111L;
 
     /**
-     * Saves the state to a stream.
+     * Saves the state to a stream (that is, serializes it).
      *
      * @serialData the current run status and the exception thrown
      * during execution, or {@code null} if none
@@ -1082,7 +1326,7 @@ public abstract class ForkJoinTask<V> im
     }
 
     /**
-     * Reconstitutes the instance from a stream.
+     * Reconstitutes the instance from a stream (that is, deserializes it).
      *
      * @param s the stream
      */
@@ -1091,23 +1335,22 @@ public abstract class ForkJoinTask<V> im
         s.defaultReadObject();
         Object ex = s.readObject();
         if (ex != null)
-            setExceptionalCompletion((Throwable) ex);
+            setExceptionalCompletion((Throwable)ex);
     }
 
     // Unsafe mechanics
-
-    private static final sun.misc.Unsafe UNSAFE = getUnsafe();
-    private static final long statusOffset =
-        objectFieldOffset("status", ForkJoinTask.class);
-
-    private static long objectFieldOffset(String field, Class<?> klazz) {
+    private static final sun.misc.Unsafe UNSAFE;
+    private static final long statusOffset;
+    static {
+        exceptionTableLock = new ReentrantLock();
+        exceptionTableRefQueue = new ReferenceQueue<Object>();
+        exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
         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;
+            UNSAFE = getUnsafe();
+            statusOffset = UNSAFE.objectFieldOffset
+                (ForkJoinTask.class.getDeclaredField("status"));
+        } catch (Exception e) {
+            throw new Error(e);
         }
     }