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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.53 by dl, Wed Aug 11 18:45:12 2010 UTC vs.
Revision 1.69 by dl, Mon Nov 22 12:24:34 2010 UTC

# Line 6 | Line 6
6  
7   package jsr166y;
8  
9 import java.util.concurrent.*;
10
9   import java.io.Serializable;
10   import java.util.Collection;
11   import java.util.Collections;
# Line 15 | Line 13 | import java.util.List;
13   import java.util.RandomAccess;
14   import java.util.Map;
15   import java.util.WeakHashMap;
16 + import java.util.concurrent.Callable;
17 + import java.util.concurrent.CancellationException;
18 + import java.util.concurrent.ExecutionException;
19 + import java.util.concurrent.Executor;
20 + import java.util.concurrent.ExecutorService;
21 + import java.util.concurrent.Future;
22 + import java.util.concurrent.RejectedExecutionException;
23 + import java.util.concurrent.RunnableFuture;
24 + import java.util.concurrent.TimeUnit;
25 + import java.util.concurrent.TimeoutException;
26  
27   /**
28   * Abstract base class for tasks that run within a {@link ForkJoinPool}.
# Line 28 | Line 36 | import java.util.WeakHashMap;
36   * start other subtasks.  As indicated by the name of this class,
37   * many programs using {@code ForkJoinTask} employ only methods
38   * {@link #fork} and {@link #join}, or derivatives such as {@link
39 < * #invokeAll}.  However, this class also provides a number of other
40 < * methods that can come into play in advanced usages, as well as
41 < * extension mechanics that allow support of new forms of fork/join
42 < * processing.
39 > * #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
40 > * provides a number of other methods that can come into play in
41 > * advanced usages, as well as extension mechanics that allow
42 > * support of new forms of fork/join processing.
43   *
44   * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
45   * The efficiency of {@code ForkJoinTask}s stems from a set of
# Line 100 | Line 108 | import java.util.WeakHashMap;
108   * ForkJoinTasks (as may be determined using method {@link
109   * #inForkJoinPool}).  Attempts to invoke them in other contexts
110   * result in exceptions or errors, possibly including
111 < * ClassCastException.
111 > * {@code ClassCastException}.
112 > *
113 > * <p>Method {@link #join} and its variants are appropriate for use
114 > * only when completion dependencies are acyclic; that is, the
115 > * parallel computation can be described as a directed acyclic graph
116 > * (DAG). Otherwise, executions may encounter a form of deadlock as
117 > * tasks cyclically wait for each other.  However, this framework
118 > * supports other methods and techniques (for example the use of
119 > * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
120 > * may be of use in constructing custom subclasses for problems that
121 > * are not statically structured as DAGs.
122   *
123   * <p>Most base support methods are {@code final}, to prevent
124   * overriding of implementations that are intrinsically tied to the
# Line 153 | Line 171 | public abstract class ForkJoinTask<V> im
171       * single int to minimize footprint and to ensure atomicity (via
172       * CAS).  Status is initially zero, and takes on nonnegative
173       * values until completed, upon which status holds value
174 <     * COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
174 >     * NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
175       * waits by other threads have the SIGNAL bit set.  Completion of
176       * a stolen task with SIGNAL set awakens any waiters via
177       * notifyAll. Even though suboptimal for some purposes, we use
# Line 205 | Line 223 | public abstract class ForkJoinTask<V> im
223      }
224  
225      /**
226 <     * Record exception and set exceptional completion
226 >     * Records exception and sets exceptional completion.
227 >     *
228       * @return status on exit
229       */
230      private void setExceptionalCompletion(Throwable rex) {
# Line 214 | Line 233 | public abstract class ForkJoinTask<V> im
233      }
234  
235      /**
236 <     * Blocks a worker thread until completion. Called only by pool.
236 >     * Blocks a worker thread until completion. Called only by
237 >     * pool. Currently unused -- pool-based waits use timeout
238 >     * version below.
239       */
240      final void internalAwaitDone() {
241          int s;         // the odd construction reduces lock bias effects
242          while ((s = status) >= 0) {
243              try {
244 <                synchronized(this) {
244 >                synchronized (this) {
245                      if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
246                          wait();
247                  }
# Line 231 | Line 252 | public abstract class ForkJoinTask<V> im
252      }
253  
254      /**
255 +     * Blocks a worker thread until completed or timed out.  Called
256 +     * only by pool.
257 +     *
258 +     * @return status on exit
259 +     */
260 +    final int internalAwaitDone(long millis, int nanos) {
261 +        int s;
262 +        if ((s = status) >= 0) {
263 +            try {
264 +                synchronized (this) {
265 +                    if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
266 +                        wait(millis, nanos);
267 +                }
268 +            } catch (InterruptedException ie) {
269 +                cancelIfTerminating();
270 +            }
271 +            s = status;
272 +        }
273 +        return s;
274 +    }
275 +
276 +    /**
277       * Blocks a non-worker-thread until completion.
278       */
279      private void externalAwaitDone() {
280          int s;
281          while ((s = status) >= 0) {
282 <            synchronized(this) {
283 <                if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
282 >            synchronized (this) {
283 >                if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
284                      boolean interrupted = false;
285                      while (status >= 0) {
286                          try {
# Line 297 | Line 340 | public abstract class ForkJoinTask<V> im
340      }
341  
342      /**
343 <     * Returns the result of the computation when it {@link #isDone is done}.
344 <     * This method differs from {@link #get()} in that
343 >     * Returns the result of the computation when it {@link #isDone is
344 >     * done}.  This method differs from {@link #get()} in that
345       * abnormal completion results in {@code RuntimeException} or
346 <     * {@code Error}, not {@code ExecutionException}.
346 >     * {@code Error}, not {@code ExecutionException}, and that
347 >     * interrupts of the calling thread do <em>not</em> cause the
348 >     * method to abruptly return by throwing {@code
349 >     * InterruptedException}.
350       *
351       * @return the computed result
352       */
# Line 314 | Line 360 | public abstract class ForkJoinTask<V> im
360  
361      /**
362       * Commences performing this task, awaits its completion if
363 <     * necessary, and return its result, or throws an (unchecked)
364 <     * exception if the underlying computation did so.
363 >     * necessary, and returns its result, or throws an (unchecked)
364 >     * {@code RuntimeException} or {@code Error} if the underlying
365 >     * computation did so.
366       *
367       * @return the computed result
368       */
# Line 330 | Line 377 | public abstract class ForkJoinTask<V> im
377      /**
378       * Forks the given tasks, returning when {@code isDone} holds for
379       * each task or an (unchecked) exception is encountered, in which
380 <     * case the exception is rethrown.  If either task encounters an
381 <     * exception, the other one may be, but is not guaranteed to be,
382 <     * cancelled.  If both tasks throw an exception, then this method
383 <     * throws one of them.  The individual status of each task may be
384 <     * checked using {@link #getException()} and related methods.
380 >     * case the exception is rethrown. If more than one task
381 >     * encounters an exception, then this method throws any one of
382 >     * these exceptions. If any task encounters an exception, the
383 >     * other may be cancelled. However, the execution status of
384 >     * individual tasks is not guaranteed upon exceptional return. The
385 >     * status of each task may be obtained using {@link
386 >     * #getException()} and related methods to check if they have been
387 >     * cancelled, completed normally or exceptionally, or left
388 >     * unprocessed.
389       *
390       * <p>This method may be invoked only from within {@code
391 <     * ForkJoinTask} computations (as may be determined using method
391 >     * ForkJoinPool} computations (as may be determined using method
392       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
393       * result in exceptions or errors, possibly including {@code
394       * ClassCastException}.
# Line 355 | Line 406 | public abstract class ForkJoinTask<V> im
406      /**
407       * Forks the given tasks, returning when {@code isDone} holds for
408       * each task or an (unchecked) exception is encountered, in which
409 <     * case the exception is rethrown. If any task encounters an
410 <     * exception, others may be, but are not guaranteed to be,
411 <     * cancelled.  If more than one task encounters an exception, then
412 <     * this method throws any one of these exceptions.  The individual
413 <     * status of each task may be checked using {@link #getException()}
414 <     * and related methods.
409 >     * case the exception is rethrown. If more than one task
410 >     * encounters an exception, then this method throws any one of
411 >     * these exceptions. If any task encounters an exception, others
412 >     * may be cancelled. However, the execution status of individual
413 >     * tasks is not guaranteed upon exceptional return. The status of
414 >     * each task may be obtained using {@link #getException()} and
415 >     * related methods to check if they have been cancelled, completed
416 >     * normally or exceptionally, or left unprocessed.
417       *
418       * <p>This method may be invoked only from within {@code
419 <     * ForkJoinTask} computations (as may be determined using method
419 >     * ForkJoinPool} computations (as may be determined using method
420       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
421       * result in exceptions or errors, possibly including {@code
422       * ClassCastException}.
# Line 407 | Line 460 | public abstract class ForkJoinTask<V> im
460      /**
461       * Forks all tasks in the specified collection, returning when
462       * {@code isDone} holds for each task or an (unchecked) exception
463 <     * is encountered.  If any task encounters an exception, others
464 <     * may be, but are not guaranteed to be, cancelled.  If more than
465 <     * one task encounters an exception, then this method throws any
466 <     * one of these exceptions.  The individual status of each task
467 <     * may be checked using {@link #getException()} and related
468 <     * methods.  The behavior of this operation is undefined if the
469 <     * specified collection is modified while the operation is in
470 <     * progress.
463 >     * is encountered, in which case the exception is rethrown. If
464 >     * more than one task encounters an exception, then this method
465 >     * throws any one of these exceptions. If any task encounters an
466 >     * exception, others may be cancelled. However, the execution
467 >     * status of individual tasks is not guaranteed upon exceptional
468 >     * return. The status of each task may be obtained using {@link
469 >     * #getException()} and related methods to check if they have been
470 >     * cancelled, completed normally or exceptionally, or left
471 >     * unprocessed.
472       *
473       * <p>This method may be invoked only from within {@code
474 <     * ForkJoinTask} computations (as may be determined using method
474 >     * ForkJoinPool} computations (as may be determined using method
475       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
476       * result in exceptions or errors, possibly including {@code
477       * ClassCastException}.
# Line 469 | Line 523 | public abstract class ForkJoinTask<V> im
523  
524      /**
525       * Attempts to cancel execution of this task. This attempt will
526 <     * fail if the task has already completed, has already been
527 <     * cancelled, or could not be cancelled for some other reason. If
528 <     * successful, and this task has not started when cancel is
529 <     * called, execution of this task is suppressed, {@link
530 <     * #isCancelled} will report true, and {@link #join} will result
531 <     * in a {@code CancellationException} being thrown.
526 >     * fail if the task has already completed or could not be
527 >     * cancelled for some other reason. If successful, and this task
528 >     * has not started when {@code cancel} is called, execution of
529 >     * this task is suppressed. After this method returns
530 >     * successfully, unless there is an intervening call to {@link
531 >     * #reinitialize}, subsequent calls to {@link #isCancelled},
532 >     * {@link #isDone}, and {@code cancel} will return {@code true}
533 >     * and calls to {@link #join} and related methods will result in
534 >     * {@code CancellationException}.
535       *
536       * <p>This method may be overridden in subclasses, but if so, must
537 <     * still ensure that these minimal properties hold. In particular,
538 <     * the {@code cancel} method itself must not throw exceptions.
537 >     * still ensure that these properties hold. In particular, the
538 >     * {@code cancel} method itself must not throw exceptions.
539       *
540       * <p>This method is designed to be invoked by <em>other</em>
541       * tasks. To terminate the current task, you can just return or
542       * throw an unchecked exception from its computation method, or
543       * invoke {@link #completeExceptionally}.
544       *
545 <     * @param mayInterruptIfRunning this value is ignored in the
546 <     * default implementation because tasks are not
547 <     * cancelled via interruption
545 >     * @param mayInterruptIfRunning this value has no effect in the
546 >     * default implementation because interrupts are not used to
547 >     * control cancellation.
548       *
549       * @return {@code true} if this task is now cancelled
550       */
# Line 510 | Line 567 | public abstract class ForkJoinTask<V> im
567      }
568  
569      /**
570 <     * Cancels ignoring exceptions if worker is terminating
570 >     * Cancels if current thread is a terminating worker thread,
571 >     * ignoring any exceptions thrown by cancel.
572       */
573      final void cancelIfTerminating() {
574          Thread t = Thread.currentThread();
# Line 587 | Line 645 | public abstract class ForkJoinTask<V> im
645  
646      /**
647       * Completes this task, and if not already aborted or cancelled,
648 <     * returning a {@code null} result upon {@code join} and related
649 <     * operations. This method may be used to provide results for
650 <     * asynchronous tasks, or to provide alternative handling for
651 <     * tasks that would not otherwise complete normally. Its use in
652 <     * other situations is discouraged. This method is
653 <     * overridable, but overridden versions must invoke {@code super}
654 <     * implementation to maintain guarantees.
648 >     * returning the given value as the result of subsequent
649 >     * invocations of {@code join} and related operations. This method
650 >     * may be used to provide results for asynchronous tasks, or to
651 >     * provide alternative handling for tasks that would not otherwise
652 >     * complete normally. Its use in other situations is
653 >     * discouraged. This method is overridable, but overridden
654 >     * versions must invoke {@code super} implementation to maintain
655 >     * guarantees.
656       *
657       * @param value the result value for this task
658       */
# Line 607 | Line 666 | public abstract class ForkJoinTask<V> im
666          setCompletion(NORMAL);
667      }
668  
669 +    /**
670 +     * Waits if necessary for the computation to complete, and then
671 +     * retrieves its result.
672 +     *
673 +     * @return the computed result
674 +     * @throws CancellationException if the computation was cancelled
675 +     * @throws ExecutionException if the computation threw an
676 +     * exception
677 +     * @throws InterruptedException if the current thread is not a
678 +     * member of a ForkJoinPool and was interrupted while waiting
679 +     */
680      public final V get() throws InterruptedException, ExecutionException {
681 <        quietlyJoin();
682 <        if (Thread.interrupted())
683 <            throw new InterruptedException();
684 <        int s = status;
681 >        int s;
682 >        if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
683 >            quietlyJoin();
684 >            s = status;
685 >        }
686 >        else {
687 >            while ((s = status) >= 0) {
688 >                synchronized (this) { // interruptible form of awaitDone
689 >                    if (UNSAFE.compareAndSwapInt(this, statusOffset,
690 >                                                 s, SIGNAL)) {
691 >                        while (status >= 0)
692 >                            wait();
693 >                    }
694 >                }
695 >            }
696 >        }
697          if (s < NORMAL) {
698              Throwable ex;
699              if (s == CANCELLED)
# Line 622 | Line 704 | public abstract class ForkJoinTask<V> im
704          return getRawResult();
705      }
706  
707 +    /**
708 +     * Waits if necessary for at most the given time for the computation
709 +     * to complete, and then retrieves its result, if available.
710 +     *
711 +     * @param timeout the maximum time to wait
712 +     * @param unit the time unit of the timeout argument
713 +     * @return the computed result
714 +     * @throws CancellationException if the computation was cancelled
715 +     * @throws ExecutionException if the computation threw an
716 +     * exception
717 +     * @throws InterruptedException if the current thread is not a
718 +     * member of a ForkJoinPool and was interrupted while waiting
719 +     * @throws TimeoutException if the wait timed out
720 +     */
721      public final V get(long timeout, TimeUnit unit)
722          throws InterruptedException, ExecutionException, TimeoutException {
723 <        Thread t = Thread.currentThread();
724 <        ForkJoinPool pool;
725 <        if (t instanceof ForkJoinWorkerThread) {
726 <            ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
727 <            if (status >= 0 && w.unpushTask(this))
728 <                quietlyExec();
729 <            pool = w.pool;
730 <        }
731 <        else
732 <            pool = null;
733 <        /*
734 <         * Timed wait loop intermixes cases for FJ (pool != null) and
735 <         * non FJ threads. For FJ, decrement pool count but don't try
736 <         * for replacement; increment count on completion. For non-FJ,
737 <         * deal with interrupts. This is messy, but a little less so
738 <         * than is splitting the FJ and nonFJ cases.
739 <         */
644 <        boolean interrupted = false;
645 <        boolean dec = false; // true if pool count decremented
646 <        for (;;) {
647 <            if (Thread.interrupted() && pool == null) {
648 <                interrupted = true;
649 <                break;
723 >        long nanos = unit.toNanos(timeout);
724 >        if (status >= 0) {
725 >            Thread t = Thread.currentThread();
726 >            if (t instanceof ForkJoinWorkerThread) {
727 >                ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
728 >                boolean completed = false; // timed variant of quietlyJoin
729 >                if (w.unpushTask(this)) {
730 >                    try {
731 >                        completed = exec();
732 >                    } catch (Throwable rex) {
733 >                        setExceptionalCompletion(rex);
734 >                    }
735 >                }
736 >                if (completed)
737 >                    setCompletion(NORMAL);
738 >                else if (status >= 0)
739 >                    w.joinTask(this, true, nanos);
740              }
741 <            int s = status;
742 <            if (s < 0)
743 <                break;
654 <            if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
741 >            else if (Thread.interrupted())
742 >                throw new InterruptedException();
743 >            else {
744                  long startTime = System.nanoTime();
745 <                long nanos = unit.toNanos(timeout);
746 <                long nt; // wait time
658 <                while (status >= 0 &&
745 >                int s; long nt;
746 >                while ((s = status) >= 0 &&
747                         (nt = nanos - (System.nanoTime() - startTime)) > 0) {
748 <                    if (pool != null && !dec)
749 <                        dec = pool.tryDecrementRunningCount();
662 <                    else {
748 >                    if (UNSAFE.compareAndSwapInt(this, statusOffset, s,
749 >                                                 SIGNAL)) {
750                          long ms = nt / 1000000;
751                          int ns = (int) (nt % 1000000);
752 <                        try {
753 <                            synchronized(this) {
754 <                                if (status >= 0)
668 <                                    wait(ms, ns);
669 <                            }
670 <                        } catch (InterruptedException ie) {
671 <                            if (pool != null)
672 <                                cancelIfTerminating();
673 <                            else {
674 <                                interrupted = true;
675 <                                break;
676 <                            }
752 >                        synchronized (this) {
753 >                            if (status >= 0)
754 >                                wait(ms, ns); // exit on IE throw
755                          }
756                      }
757                  }
680                break;
758              }
759          }
683        if (pool != null && dec)
684            pool.incrementRunningCount();
685        if (interrupted)
686            throw new InterruptedException();
760          int es = status;
761          if (es != NORMAL) {
762              Throwable ex;
# Line 720 | Line 793 | public abstract class ForkJoinTask<V> im
793                          return;
794                      }
795                  }
796 <                w.joinTask(this);
796 >                w.joinTask(this, false, 0L);
797              }
798          }
799          else
# Line 730 | Line 803 | public abstract class ForkJoinTask<V> im
803      /**
804       * Commences performing this task and awaits its completion if
805       * necessary, without returning its result or throwing its
806 <     * exception. This method may be useful when processing
734 <     * collections of tasks when some have been cancelled or otherwise
735 <     * known to have aborted.
806 >     * exception.
807       */
808      public final void quietlyInvoke() {
809          if (status >= 0) {
# Line 758 | Line 829 | public abstract class ForkJoinTask<V> im
829       * processed.
830       *
831       * <p>This method may be invoked only from within {@code
832 <     * ForkJoinTask} computations (as may be determined using method
832 >     * ForkJoinPool} computations (as may be determined using method
833       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
834       * result in exceptions or errors, possibly including {@code
835       * ClassCastException}.
# Line 777 | Line 848 | public abstract class ForkJoinTask<V> im
848       * under any other usage conditions are not guaranteed.
849       * This method may be useful when executing
850       * pre-constructed trees of subtasks in loops.
851 +     *
852 +     * <p>Upon completion of this method, {@code isDone()} reports
853 +     * {@code false}, and {@code getException()} reports {@code
854 +     * null}. However, the value returned by {@code getRawResult} is
855 +     * unaffected. To clear this value, you can invoke {@code
856 +     * setRawResult(null)}.
857       */
858      public void reinitialize() {
859          if (status == EXCEPTIONAL)
# Line 817 | Line 894 | public abstract class ForkJoinTask<V> im
894       * were not, stolen.
895       *
896       * <p>This method may be invoked only from within {@code
897 <     * ForkJoinTask} computations (as may be determined using method
897 >     * ForkJoinPool} computations (as may be determined using method
898       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
899       * result in exceptions or errors, possibly including {@code
900       * ClassCastException}.
# Line 836 | Line 913 | public abstract class ForkJoinTask<V> im
913       * fork other tasks.
914       *
915       * <p>This method may be invoked only from within {@code
916 <     * ForkJoinTask} computations (as may be determined using method
916 >     * ForkJoinPool} computations (as may be determined using method
917       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
918       * result in exceptions or errors, possibly including {@code
919       * ClassCastException}.
# Line 859 | Line 936 | public abstract class ForkJoinTask<V> im
936       * exceeded.
937       *
938       * <p>This method may be invoked only from within {@code
939 <     * ForkJoinTask} computations (as may be determined using method
939 >     * ForkJoinPool} computations (as may be determined using method
940       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
941       * result in exceptions or errors, possibly including {@code
942       * ClassCastException}.
# Line 917 | Line 994 | public abstract class ForkJoinTask<V> im
994       * otherwise.
995       *
996       * <p>This method may be invoked only from within {@code
997 <     * ForkJoinTask} computations (as may be determined using method
997 >     * ForkJoinPool} computations (as may be determined using method
998       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
999       * result in exceptions or errors, possibly including {@code
1000       * ClassCastException}.
# Line 936 | Line 1013 | public abstract class ForkJoinTask<V> im
1013       * be useful otherwise.
1014       *
1015       * <p>This method may be invoked only from within {@code
1016 <     * ForkJoinTask} computations (as may be determined using method
1016 >     * ForkJoinPool} computations (as may be determined using method
1017       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1018       * result in exceptions or errors, possibly including {@code
1019       * ClassCastException}.
# Line 959 | Line 1036 | public abstract class ForkJoinTask<V> im
1036       * otherwise.
1037       *
1038       * <p>This method may be invoked only from within {@code
1039 <     * ForkJoinTask} computations (as may be determined using method
1039 >     * ForkJoinPool} computations (as may be determined using method
1040       * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1041       * result in exceptions or errors, possibly including {@code
1042       * ClassCastException}.
# Line 1069 | Line 1146 | public abstract class ForkJoinTask<V> im
1146      private static final long serialVersionUID = -7721805057305804111L;
1147  
1148      /**
1149 <     * Saves the state to a stream.
1149 >     * Saves the state to a stream (that is, serializes it).
1150       *
1151       * @serialData the current run status and the exception thrown
1152       * during execution, or {@code null} if none
# Line 1082 | Line 1159 | public abstract class ForkJoinTask<V> im
1159      }
1160  
1161      /**
1162 <     * Reconstitutes the instance from a stream.
1162 >     * Reconstitutes the instance from a stream (that is, deserializes it).
1163       *
1164       * @param s the stream
1165       */

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