//******************************************************************************
   //
   // File:    WorkerIntegerStrideForLoop.java
   // Package: edu.rit.pj
   // Unit:    Class edu.rit.pj.WorkerIntegerStrideForLoop
   //
   // This Java source file is copyright (C) 2010 by Alan Kaminsky. All rights
   // reserved. For further information, contact the author, Alan Kaminsky, at
   // ark@cs.rit.edu.
  //
  // This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
  // software; you can redistribute it and/or modify it under the terms of the GNU
  // General Public License as published by the Free Software Foundation; either
  // version 3 of the License, or (at your option) any later version.
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  // WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  // A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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  // Linking this library statically or dynamically with other modules is making a
  // combined work based on this library. Thus, the terms and conditions of the GNU
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  // permission to link this library with independent modules to produce an
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  //******************************************************************************
  package edu.rit.pj;
  
  import java.io.IOException;
  
  import edu.rit.mp.ObjectBuf;
  import edu.rit.mp.buf.ObjectItemBuf;
  import edu.rit.util.Range;
  
  /**
   * Class WorkerIntegerStrideForLoop is the abstract base class for one variation
   * of a worker for loop that is executed inside a {@linkplain WorkerRegion}. The
   * loop index data type is <code>int</code>. The loop stride is explicitly
   * specified.
   * <P>
   * To execute a worker for loop, create a {@linkplain WorkerRegion} object;
   * create an instance of a concrete subclass of class
   * WorkerIntegerStrideForLoop; and pass this instance to the worker region's
   * <code>execute()</code> method. Either every worker team thread must call the
   * worker region's <code>execute()</code> method with identical arguments, or every
   * thread must not call the <code>execute()</code> method. You can do all this using
   * an anonymous inner class; for example:
   * <PRE>
   *     new WorkerRegion()
   *         {
   *         . . .
   *         public void run()
   *             {
   *             . . .
   *             execute (0, 98, 2, new WorkerIntegerStrideForLoop()
   *                 {
   *                 // Thread local variable declarations
   *                 . . .
   *                 public void start()
   *                     {
   *                     // Per-thread pre-loop initialization code
   *                     . . .
   *                     }
   *                 public void run (int first, int last, int stride)
   *                     {
   *                     // Loop code
   *                     . . .
   *                     }
   *                 public void finish()
   *                     {
   *                     // Per-thread post-loop finalization code
   *                     . . .
   *                     }
   *                 });
   *             }
   *         . . .
   *         }
   * </PRE>
   * <P>
   * In each process of a cluster parallel program, the worker team has one or
   * more worker threads. Every worker thread in every process has a unique worker
   * tag, going from tag 0 for the first worker thread in the first process to tag
   * <I>K</I>&minus;1 for the last worker thread in the last process, where
   * <I>K</I> is the total number of worker threads in all the processes. In
   * addition, in one process there is a master thread. The worker and master
   * threads all call the worker region's <code>execute()</code> method to execute the
  * worker for loop. However, the worker and master threads differ in their
  * actions.
  * <P>
  * The master thread does the following. The master obtains the worker for
  * loop's schedule as returned by the <code>schedule()</code> method. The range of
  * loop indexes is divided into "chunks" and the chunks are apportioned among
  * the workers in accordance with the schedule. The master repeatedly sends
  * "tasks" to the workers and receives "responses" from the workers. To send a
  * task to a particular worker, the master (1) sends a message containing the
  * chunk index range to the worker's process; and (2) calls the worker for
  * loop's <code>sendTaskInput()</code> method. This method's default implementation
  * does nothing, but it can be overridden to send additional task input data to
  * the worker. To receive a response from a particular worker, the master (1)
  * receives a message containing the chunk index range from the worker's
  * process; and (2) calls the worker for loop's <code>receiveTaskOutput()</code>
  * method. This method's default implementation does nothing, but it can be
  * overridden to receive additional task output data from the worker. Once all
  * tasks have been sent to the workers and all responses have been received from
  * the workers, the master returns from the worker region's <code>execute()</code>
  * method.
  * <P>
  * Each worker thread does the following. The worker calls the worker for loop's
  * <code>start()</code> method once before beginning any loop iterations. The worker
  * repeatedly receives tasks from the master and sends responses to the master.
  * To receive a task from the master, the worker (1) receives a message
  * containing the chunk index range from the master's process; and (2) calls the
  * worker for loop's <code>receiveTaskInput()</code> method. This method's default
  * implementation does nothing, but it can be overridden to receive additional
  * task input data from the master. The worker now calls the worker for loop's
  * <code>run()</code> method, passing in the chunk index range lower and upper
  * bounds. When the <code>run()</code> method returns, the worker sends the response
  * to the master. To send the response, the worker (1) sends a message
  * containing the chunk index range to the master's process; and (2) calls the
  * worker for loop's <code>sendTaskOutput()</code> method. This method's default
  * implementation does nothing, but it can be overridden to send additional task
  * output data to the master. Once all tasks have been received from the master
  * and all responses have been sent to the master, the worker calls the worker
  * for loop's <code>finish()</code> method. (Unlike a {@linkplain ParallelTeam}'s
  * threads, the workers do <I>not</I> synchronize with each other at a barrier
  * at this point.) The worker then returns from the worker region's
  * <code>execute()</code> method.
  * <P>
  * If the worker for loop has a fixed schedule (in which there is exactly one
  * chunk with a predetermined index range for each worker), then the messages
  * containing the chunk index range are omitted, and each worker gets its chunk
  * index range directly from the fixed schedule. However, the task input data
  * (if any) and task output data (if any) are still sent and received.
  * <P>
  * Each message described above is sent with a message tag equal to
  * <I>W</I>+<I>T</I>, where <I>W</I> is the worker index and <I>T</I> is the
  * "tag offset." The tag offset is <code>Integer.MIN_VALUE</code> by default, but
  * this can be changed by overriding the <code>tagOffset()</code> method. Thus, the
  * message tags fall in the range <I>T</I> .. <I>K</I>&minus;1+<I>T</I>, where
  * <I>K</I> is the total number of workers in all the processes. The program
  * should not use message tags in this range except to send and receive the
  * messages described above.
  * <P>
  * Note that each worker team thread actually creates its own instance of the
  * worker for loop class and passes that instance to the worker region's
  * <code>execute()</code> method. Thus, any fields declared in the worker for loop
  * class will <I>not</I> be shared by all the workers, but instead will be
  * private to each worker.
  * <P>
  * The <code>start()</code> method is intended for performing per-thread
  * initialization before starting the loop iterations. If no such initialization
  * is needed, omit the <code>start()</code> method.
  * <P>
  * The <code>run()</code> method contains the code for the loop. The first and last
  * indexes for a chunk of loop iterations are passed in as arguments. The loop
  * stride, which is always positive, is also explicitly specified as an
  * argument. The worker for loop's <code>run()</code> method must be coded this way:
  * <PRE>
  *     public void run (int first, int last, int stride)
  *         {
  *         for (int i = first; i &lt;= last; i += stride)
  *             {
  *             // Loop body code
  *             . . .
  *             }
  *         }
  * </PRE> with the loop indexes running from <code>first</code> to <code>last</code>
  * inclusive and increasing by <code>stride</code> on each iteration.
  * <P>
  * The <code>finish()</code> method is intended for performing per-thread
  * finalization after finishing the loop iterations. If no such finalization is
  * needed, omit the <code>finish()</code> method.
  * <P>
  * If the worker for loop's <code>start()</code>, <code>run()</code>, or
  * <code>finish()</code> method throws an exception in one of the worker threads,
  * then that worker thread executes no further code in the loop, and the worker
  * region's <code>execute()</code> method throws that same exception in that thread.
  * However, the other worker threads in the worker team continue to execute.
  *
  * @author Alan Kaminsky
  * @version 27-Jan-2010
  */
 public abstract class WorkerIntegerStrideForLoop
         extends WorkerForLoop {
 
 // Exported constructors.
     /**
      * Construct a new worker for loop.
      */
     public WorkerIntegerStrideForLoop() {
         super();
     }
 
 // Exported operations.
     /**
      * Determine this worker for loop's schedule. Called by the master and
      * worker threads. The schedule determines how the loop iterations are
      * apportioned among the worker team threads. For further information, see
      * class {@linkplain IntegerSchedule}.
      * <P>
      * The <code>schedule()</code> method may be overridden in a subclass to return
      * the desired schedule. If not overridden, the default is a runtime
      * schedule (see {@link edu.rit.pj.IntegerSchedule#runtime()}).
      *
      * @return Schedule for this worker for loop.
      */
     public IntegerSchedule schedule() {
         return IntegerSchedule.runtime();
     }
 
     /**
      * Perform per-thread initialization actions before starting the loop
      * iterations. Called by a worker thread.
      * <P>
      * The <code>start()</code> method may be overridden in a subclass. If not
      * overridden, the <code>start()</code> method does nothing.
      *
      * @exception Exception The <code>start()</code> method may throw any exception.
      * @throws java.lang.Exception if any.
      */
     public void start()
             throws Exception {
     }
 
     /**
      * Send additional input data associated with a task. Called by the master
      * thread. The task is denoted by the given chunk of loop iterations. The
      * input data must be sent using the given communicator, to the given worker
      * process rank, with the given message tag.
      * <P>
      * The <code>sendTaskInput()</code> method may be overridden in a subclass. If
      * not overridden, the <code>sendTaskInput()</code> method does nothing.
      *
      * @param range Chunk of loop iterations.
      * @param comm Communicator.
      * @param wRank Worker process rank.
      * @param tag Message tag.
      * @exception IOException Thrown if an I/O error occurred.
      * @throws java.io.IOException if any.
      */
     public void sendTaskInput(Range range,
             Comm comm,
             int wRank,
             int tag)
             throws IOException {
     }
 
     /**
      * Receive additional input data associated with a task. Called by a worker
      * thread. The task is denoted by the given chunk of loop iterations. The
      * input data must be received using the given communicator, from the given
      * master process rank, with the given message tag.
      * <P>
      * The <code>receiveTaskInput()</code> method may be overridden in a subclass.
      * If not overridden, the <code>receiveTaskInput()</code> method does nothing.
      *
      * @param range Chunk of loop iterations.
      * @param comm Communicator.
      * @param mRank Master process rank.
      * @param tag Message tag.
      * @exception IOException Thrown if an I/O error occurred.
      * @throws java.io.IOException if any.
      */
     public void receiveTaskInput(Range range,
             Comm comm,
             int mRank,
             int tag)
             throws IOException {
     }
 
     /**
      * Execute one chunk of iterations of this worker for loop. Called by a
      * worker thread. The <code>run()</code> method must perform the loop body for
      * indexes <code>first</code> through <code>last</code> inclusive, increasing the
      * loop index by <code>stride</code> after each iteration.
      * <P>
      * The <code>run()</code> method must be overridden in a subclass.
      *
      * @param first First loop index.
      * @param last Last loop index.
      * @param stride Loop index stride, always positive.
      * @exception Exception The <code>run()</code> method may throw any exception.
      * @throws java.lang.Exception if any.
      */
     public abstract void run(int first,
             int last,
             int stride)
             throws Exception;
 
     /**
      * Send additional output data associated with a task. Called by a worker
      * thread. The task is denoted by the given chunk of loop iterations. The
      * output data must be sent using the given communicator, to the given
      * master process rank, with the given message tag.
      * <P>
      * The <code>sendTaskOutput()</code> method may be overridden in a subclass. If
      * not overridden, the <code>sendTaskOutput()</code> method does nothing.
      *
      * @param range Chunk of loop iterations.
      * @param comm Communicator.
      * @param mRank Master process rank.
      * @param tag Message tag.
      * @exception IOException Thrown if an I/O error occurred.
      * @throws java.io.IOException if any.
      */
     public void sendTaskOutput(Range range,
             Comm comm,
             int mRank,
             int tag)
             throws IOException {
     }
 
     /**
      * Receive additional output data associated with a task. Called by the
      * master thread. The task is denoted by the given chunk of loop iterations.
      * The output data must be received using the given communicator, from the
      * given worker process rank, with the given message tag.
      * <P>
      * The <code>receiveTaskOutput()</code> method may be overridden in a subclass.
      * If not overridden, the <code>receiveTaskOutput()</code> method does nothing.
      *
      * @param range Chunk of loop iterations.
      * @param comm Communicator.
      * @param wRank Worker process rank.
      * @param tag Message tag.
      * @exception IOException Thrown if an I/O error occurred.
      * @throws java.io.IOException if any.
      */
     public void receiveTaskOutput(Range range,
             Comm comm,
             int wRank,
             int tag)
             throws IOException {
     }
 
     /**
      * Perform per-thread finalization actions after finishing the loop
      * iterations. Called by a worker thread.
      * <P>
      * The <code>finish()</code> method may be overridden in a subclass. If not
      * overridden, the <code>finish()</code> method does nothing.
      *
      * @exception Exception The <code>finish()</code> method may throw any
      * exception.
      * @throws java.lang.Exception if any.
      */
     public void finish()
             throws Exception {
     }
 
     /**
      * Returns the tag offset for this worker for loop. Each message between the
      * master and worker threads is sent with a message tag equal to
      * <I>W</I>+<I>T</I>, where <I>W</I> is the worker index and <I>T</I> is the
      * tag offset.
      * <P>
      * The <code>tagOffset()</code> method may be overridden in a subclass. If not
      * overridden, the <code>tagOffset()</code> returns a default tag offset of
      * <code>Integer.MIN_VALUE</code>.
      *
      * @return Tag offset.
      */
     public int tagOffset() {
         return Integer.MIN_VALUE;
     }
 
 // Hidden operations.
     /**
      * Execute this worker for loop in the master thread.
      *
      * @param range Loop index range.
      *
      * @exception IOException Thrown if an I/O error occurred.
      */
     void masterExecute(Range range)
             throws IOException {
         IntegerSchedule sch = schedule();
         if (sch.isFixedSchedule()) {
             masterExecuteFixed(range, sch);
         } else {
             masterExecuteNonFixed(range, sch);
         }
     }
 
     /**
      * Execute this worker for loop in the master thread with a fixed schedule.
      *
      * @param range Loop index range.
      * @param sch Schedule.
      *
      * @exception IOException Thrown if an I/O error occurred.
      */
     void masterExecuteFixed(Range range,
             IntegerSchedule sch)
             throws IOException {
         int count = myTeam.count;
         Comm comm = myTeam.comm;
 
         // Send additional task input to each worker.
         sch.start(count, range);
         for (int w = 0; w < count; ++w) {
             Range chunk = sch.next(w);
             if (chunk != null) {
                 sendTaskInput(chunk, comm, myTeam.workerRank(w), tagFor(w));
             }
         }
 
         // Receive additional task output from each worker.
         sch.start(count, range);
         for (int w = 0; w < count; ++w) {
             Range chunk = sch.next(w);
             if (chunk != null) {
                 receiveTaskOutput(chunk, comm, myTeam.workerRank(w), tagFor(w));
             }
         }
     }
 
     /**
      * Execute this worker for loop in the master thread with a non-fixed
      * schedule.
      *
      * @param range Loop index range.
      * @param sch Schedule.
      *
      * @exception IOException Thrown if an I/O error occurred.
      */
     void masterExecuteNonFixed(Range range,
             IntegerSchedule sch)
             throws IOException {
         int count = myTeam.count;
         sch.start(count, range);
         int remaining = count;
         ObjectItemBuf<Range> buf = ObjectBuf.buffer();
         Range tagRange = new Range(tagFor(0), tagFor(count - 1));
         Comm comm = myTeam.comm;
 
         // Send initial task to each worker.
         for (int w = 0; w < count; ++w) {
             Range chunk = sch.next(w);
             buf.item = chunk;
             buf.reset();
             int r = myTeam.workerRank(w);
             int tag = tagFor(w);
             comm.send(r, tag, buf);
             if (chunk == null) {
                 --remaining;
             } else {
                 sendTaskInput(chunk, comm, r, tag);
             }
         }
 
         // Repeatedly receive a response from a worker and send next task to
         // that worker.
         while (remaining > 0) {
             CommStatus status = comm.receive(null, tagRange, buf);
             Range chunk = buf.item;
             int r = status.fromRank;
             int tag = status.tag;
             int w = workerFor(tag);
             receiveTaskOutput(chunk, comm, r, tag);
             chunk = sch.next(w);
             buf.item = chunk;
             buf.reset();
             comm.send(r, tag, buf);
             if (chunk == null) {
                 --remaining;
             } else {
                 sendTaskInput(chunk, comm, r, tag);
             }
         }
     }
 
     /**
      * Execute this worker for loop in a worker thread.
      *
      * @param tag Worker tag.
      * @param range Loop index range.
      *
      * @exception Exception This method may throw any exception.
      */
     void workerExecute(int tag,
             Range range)
             throws Exception {
         IntegerSchedule sch = schedule();
         if (sch.isFixedSchedule()) {
             sch.start(myTeam.count, range);
             workerExecuteFixed(sch.next(tag), tag);
         } else {
             workerExecuteNonFixed(tag);
         }
     }
 
     /**
      * Execute this worker for loop in a worker thread using a fixed schedule.
      *
      * @param range Chunk of loop iterations.
      * @param w Worker index.
      *
      * @exception Exception This method may throw any exception.
      */
     void workerExecuteFixed(Range range,
             int w)
             throws Exception {
         start();
         if (range != null) {
             Comm comm = myTeam.comm;
             int r = myTeam.masterRank();
             int tag = tagFor(w);
             receiveTaskInput(range, comm, r, tag);
             run(range.lb(), range.ub(), range.stride());
             sendTaskOutput(range, comm, r, tag);
         }
         finish();
     }
 
     /**
      * Execute this worker for loop in a worker thread using a non-fixed
      * schedule.
      *
      * @param w Worker index.
      *
      * @exception Exception This method may throw any exception.
      */
     void workerExecuteNonFixed(int w)
             throws Exception {
         Comm comm = myTeam.comm;
         int r = myTeam.masterRank();
         int tag = tagFor(w);
         start();
         ObjectItemBuf<Range> buf = ObjectBuf.buffer();
         for (;;) {
             comm.receive(r, tag, buf);
             Range range = buf.item;
             if (range == null) {
                 break;
             }
             receiveTaskInput(range, comm, r, tag);
             run(range.lb(), range.ub(), range.stride());
 
             // The next two statements constitute a critical section; other
             // workers in this team must not send messages in between these two
             // messages, or the master can deadlock.
             synchronized (myTeam) {
                 comm.send(r, tag, buf);
                 sendTaskOutput(range, comm, r, tag);
             }
         }
         finish();
     }
 
     /**
      * Returns the message tag for the given worker index.
      *
      * @param w Worker index.
      *
      * @return Message tag.
      */
     private int tagFor(int w) {
         return w + tagOffset();
     }
 
     /**
      * Returns the worker index for the given message tag.
      *
      * @param tag Message tag.
      *
      * @return Worker index.
      */
     private int workerFor(int tag) {
         return tag - tagOffset();
     }
 
 }