//******************************************************************************
   //
   // File:    WorkerIteration.java
   // Package: edu.rit.pj
   // Unit:    Class edu.rit.pj.WorkerIteration
   //
   // 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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  // combined work based on this library. Thus, the terms and conditions of the GNU
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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 WorkerIteration is the abstract base class for a worker iteration that
   * is executed inside a {@linkplain WorkerRegion}. The worker iteration lets you
   * iterate over a group of items, with a separate worker team thread processing
   * each item. The generic type parameter T specifies the items' data type. The
   * items can be the elements of an array, the items obtained from an {@linkplain
   * java.util.Iterator Iterator}, or the items contained in an {@linkplain
   * java.lang.Iterable Iterable} collection.
   * <P>
   * To execute a worker iteration, create a {@linkplain WorkerRegion} object;
   * create an instance of a concrete subclass of class WorkerIteration; 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()
   *         {
   *         ArrayList&lt;String&gt; list = new ArrayList&lt;String&gt;();
   *         . . .
   *         public void run()
   *             {
   *             . . .
   *             execute (list, new WorkerIteration&lt;String&gt;()
   *                 {
   *                 // Thread local variable declarations
   *                 . . .
   *                 public void start()
   *                     {
   *                     // Per-thread pre-loop initialization code
   *                     . . .
   *                     }
   *                 public void run (String item)
   *                     {
   *                     // 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
   * index, going from index 0 for the first worker thread in the first process to
  * index <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 sets up the source of items
  * to be iterated over -- either an array's elements, an iterator's items, or an
  * iterable collection's contents. 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 next item to
  * the worker's process; and (2) calls the worker iteration'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 from the worker's process containing the item that was
  * processed (whose state may have changed); and (2) calls the worker
  * iteration'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
  * iteration's <code>start()</code> method once before processing any items. 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 next item from the master's process; and (2) calls the worker
  * iteration'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 iteration's
  * <code>run()</code> method, passing in the item to be processed. 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 to the master's process
  * containing the item that was processed (whose state may have changed); and
  * (2) calls the worker iteration'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 iteration's <code>finish()</code> method. (Unlike a
  * {@linkplain ParallelIteration}'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>
  * 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 iteration class and passes that instance to the worker region's
  * <code>execute()</code> method. Thus, any fields declared in the worker iteration
  * 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 body. It does
  * whatever processing is needed on the one item passed in as an argument. Note
  * that, unlike a worker for loop (class {@linkplain WorkerForLoop}), a worker
  * iteration is not "chunked;" each worker team thread always processes just one
  * item at a time.
  * <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 iteration'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.
  *
  * @param <T> Data type of the items iterated over.
  * @author Alan Kaminsky
  * @version 07-Oct-2010
  */
 public abstract class WorkerIteration<T>
         extends WorkerConstruct {
 
 // Exported constructors.
     /**
      * Construct a new worker iteration.
      */
     public WorkerIteration() {
         super();
     }
 
 // Exported operations.
     /**
      * 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 item to be processed. 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 item Item to be processed.
      * @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(T item,
             Comm comm,
             int wRank,
             int tag)
             throws IOException {
     }
 
     /**
      * Receive input data associated with a task. Called by a worker thread. The
      * task is denoted by the given item to be processed. 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 item Item to be processed.
      * @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(T item,
             Comm comm,
             int mRank,
             int tag)
             throws IOException {
     }
 
     /**
      * Process one item in this worker iteration. The <code>run()</code> method must
      * perform the loop body for the given item.
      * <P>
      * The <code>run()</code> method must be overridden in a subclass.
      *
      * @param item Item.
      * @exception Exception The <code>run()</code> method may throw any exception.
      * @throws java.lang.Exception if any.
      */
     public abstract void run(T item)
             throws Exception;
 
     /**
      * Send additional output data associated with a task. Called by a worker
      * thread. The task is denoted by the given item that was processed (whose
      * state may have changed during processing). 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 item Item that was processed.
      * @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(T item,
             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 item that was processed
      * (whose state may have changed during processing). 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 item Item that was processed.
      * @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(T item,
             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 iteration in the master thread.
      *
      * @param generator Item generator.
      *
      * @exception IOException Thrown if an I/O error occurred.
      */
     void masterExecute(ItemGenerator<T> generator)
             throws IOException {
         int count = myTeam.count;
         int remaining = count;
         ObjectItemBuf<ItemHolder<T>> 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) {
             ItemHolder<T> holder = generator.nextItem();
             buf.item = holder;
             buf.reset();
             int r = myTeam.workerRank(w);
             int tag = tagFor(w);
             comm.send(r, tag, buf);
             if (holder == null) {
                 --remaining;
             } else {
                 sendTaskInput(holder.myItem, 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);
             ItemHolder<T> holder = buf.item;
             int r = status.fromRank;
             int tag = status.tag;
             int w = workerFor(tag);
             receiveTaskOutput(holder.myItem, comm, r, tag);
             holder = generator.nextItem();
             buf.item = holder;
             buf.reset();
             comm.send(r, tag, buf);
             if (holder == null) {
                 --remaining;
             } else {
                 sendTaskInput(holder.myItem, comm, r, tag);
             }
         }
     }
 
     /**
      * Execute this worker for loop in a worker thread.
      *
      * @param w Worker index.
      *
      * @exception Exception This method may throw any exception.
      */
     void workerExecute(int w)
             throws Exception {
         Comm comm = myTeam.comm;
         int r = myTeam.masterRank();
         int tag = tagFor(w);
         start();
         ObjectItemBuf<ItemHolder<T>> buf = ObjectBuf.buffer();
         for (;;) {
             comm.receive(r, tag, buf);
             ItemHolder<T> holder = buf.item;
             if (holder == null) {
                 break;
             }
             receiveTaskInput(holder.myItem, comm, r, tag);
             run(holder.myItem);
             buf.reset();
 
             // 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(holder.myItem, 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();
     }
 
 }