//******************************************************************************
   //
   // File:    ParallelTeam.java
   // Package: edu.rit.pj
   // Unit:    Class edu.rit.pj.ParallelTeam
   //
   // This Java source file is copyright (C) 2008 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.
  //
  // PJ is distributed in the hope that it will be useful, but WITHOUT ANY
  // WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  // A PARTICULAR PURPOSE. See the GNU General Public License for more details.
  //
  // 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
  // General Public License cover the whole combination.
  //
  // As a special exception, the copyright holders of this library give you
  // permission to link this library with independent modules to produce an
  // executable, regardless of the license terms of these independent modules, and
  // to copy and distribute the resulting executable under terms of your choice,
  // provided that you also meet, for each linked independent module, the terms
  // and conditions of the license of that module. An independent module is a module
  // which is not derived from or based on this library. If you modify this library,
  // you may extend this exception to your version of the library, but you are not
  // obligated to do so. If you do not wish to do so, delete this exception
  // statement from your version.
  //
  // A copy of the GNU General Public License is provided in the file gpl.txt. You
  // may also obtain a copy of the GNU General Public License on the World Wide
  // Web at http://www.gnu.org/licenses/gpl.html.
  //
  //******************************************************************************
  
  //******************************************************************************
  // File modified 10/8/2014 by Jacob Litman to enable garbage collection of
  // ParallelTeamThreads.
  //******************************************************************************
  package edu.rit.pj;
  
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.Semaphore;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * Class ParallelTeam provides a team of threads for executing a {@linkplain
   * ParallelRegion} in parallel.
   * <P>
   * To execute a parallel region, create a ParallelTeam object; create an
   * instance of a concrete subclass of class {@linkplain ParallelRegion}; and
   * pass this instance to the parallel team's <code>execute()</code> method. For
   * further information, see class {@linkplain ParallelRegion}.
   *
   * @author Alan Kaminsky
   * @version 19-May-2008
   */
  public class ParallelTeam {
  
  // Hidden data members.
      // Number of threads.
      int K;
  
      // Array of threads in the team.
      ParallelTeamThread[] myThread;
  
      // Parallel region being executed, or null if none is being executed.
      ParallelRegion myRegion;
  
      // Semaphore for synchronizing threads at the end of a parallel region.
      Semaphore myRegionEndSemaphore = new Semaphore(0);
  
      // Exception map for parallel region, or null if none is being executed.
      ConcurrentHashMap<Integer, Throwable> myExceptionMap;
  
      // Team barrier flag. Used by the ParallelRegion.barrier() method.
      volatile int myBarrierFlag;
  
      // Parallel construct counter. Counts how many parallel constructs have been
      // encountered.
      AtomicInteger myConstructCount = new AtomicInteger(0);
      
      // Set false if the ParallelTeam is shut down.
      boolean isActive = true;
  
  // Exported constructors.
      /**
       * Construct a new parallel team with the default number of threads. If the
       * <code>"pj.nt"</code> Java property is specified, that property gives the
       * default number of threads, which must be an integer greater than or equal
       * to 1. If the <code>"pj.nt"</code> Java property is not specified, the default
       * number of threads is the value returned by the
       * <code>Runtime.availableProcessors()</code> method. You can specify the
       * default number of threads on the Java command line like this:
      * <PRE>
      *     java -Dpj.nt=4 . . .
      * </PRE>
      *
      * @exception IllegalArgumentException (unchecked exception) Thrown if the
      * <code>"pj.nt"</code> property value is not an integer greater than or equal
      * to 1.
      */
     public ParallelTeam() {
         this(getDefaultThreadCount());
     }
 
     /**
      * Construct a new parallel team with the given number of threads.
      *
      * @param K Number of threads.
      * @exception IllegalArgumentException (unchecked exception) Thrown if
      * <I>K</I> is less than 1.
      */
     public ParallelTeam(int K) {
         if (K < 1) {
             throw new IllegalArgumentException("ParallelTeam(): K must be >= 1");
         }
         this.K = K;
 
         myThread = new ParallelTeamThread[K];
         myThread[0] = new ParallelTeamThread_0(this, 0);
         for (int i = 1; i < K; ++i) {
             myThread[i] = new ParallelTeamThread(this, i);
         }
     }
 
 // Exported operations.
     /**
      * Execute the given parallel region.
      *
      * @param theRegion Parallel region.
      * @exception NullPointerException (unchecked exception) Thrown if
      * <code>theRegion</code> is null.
      * @exception IllegalStateException (unchecked exception) Thrown if this
      * parallel team is already executing a parallel region. Thrown if
      * <code>theRegion</code> is already being executed by a parallel team.
      * @exception Exception Exception thrown by the parallel region's
      * <code>start()</code>,
      * <code>run()</code>, or <code>finish()</code> methods.
      * @throws java.lang.Exception if any.
      */
     public final void execute(ParallelRegion theRegion)
             throws Exception {
         // Verify preconditions.
         if (theRegion == null) {
             throw new NullPointerException("ParallelTeam.execute(): theRegion is null");
         }
         if (myRegion != null) {
             throw new IllegalStateException("ParallelTeam.execute(): Already executing a parallel region");
         }
         if (theRegion.myTeam != null) {
             throw new IllegalStateException("ParallelTeam.execute(): theRegion already being executed by a parallel team");
         }
         if (!isActive) {
             throw new IllegalStateException("ParallelTeam.execute(): The team has been shut down.");
         }
 
         // Record parallel region.
         myRegion = theRegion;
         myExceptionMap = new ConcurrentHashMap<>(K, 0.75f, K);
         theRegion.myTeam = this;
 
         try {
             // Perform the parallel region's start() method. Any exception
             // aborts the execute() method.
             myRegion.start();
 
             // Release the team threads to perform the parallel region's run()
             // method.
             for (ParallelTeamThread thread : myThread) {
                 thread.myRegionBeginSemaphore.release();
             }
 
             // Wait until all team threads have returned from the parallel
             // region's run() method.
             myRegionEndSemaphore.acquireUninterruptibly(K);
 
             // Propagate any exceptions thrown by the run() method.
             if (myExceptionMap.isEmpty()) {
             } else if (myExceptionMap.size() == 1) {
                 rethrow(myExceptionMap.values().iterator().next());
             } else {
                 throw new MultipleParallelException("ParallelTeam.execute(): Multiple threads threw exceptions",
                         myExceptionMap);
             }
 
             // Perform the parallel region's finish() method. Any exception
             // aborts the execute() method.
             myRegion.finish();
         } finally {
             // Clean up.
             myRegion.myTeam = null;
             myExceptionMap = null;
             myRegion = null;
         }
     }
 
     /**
      * Determine if this parallel team is executing a parallel region.
      *
      * @return True if this parallel team is executing a parallel region, false
      * otherwise.
      */
     public final boolean isExecutingInParallel() {
         return myRegion != null;
     }
 
     /**
      * Returns the parallel region of code that this parallel team is executing.
      *
      * @return Parallel region.
      * @exception IllegalStateException (unchecked exception) Thrown if this
      * parallel team is not executing a parallel region.
      */
     public final ParallelRegion region() {
         if (myRegion == null) {
             throw new IllegalStateException("ParallelTeam.region(): Not executing a parallel region");
         }
         return myRegion;
     }
 
     /**
      * Determine the number of threads in this parallel team.
      *
      * @return Number of threads in the team.
      */
     public final int getThreadCount() {
         return K;
     }
 
     /**
      * Determine the default number of threads for a parallel team. If the
      * <code>"pj.nt"</code> Java property is specified, that property gives the
      * default number of threads, which must be an integer greater than or equal
      * to 1. If the <code>"pj.nt"</code> Java property is not specified, the default
      * number of threads is the value returned by the
      * <code>Runtime.availableProcessors()</code> method. You can specify the
      * default number of threads on the Java command line like this:
      * <PRE>
      *     java -Dpj.nt=4 . . .
      * </PRE>
      *
      * @return Default number of threads for a parallel team.
      * @exception IllegalArgumentException (unchecked exception) Thrown if the
      * <code>"pj.nt"</code> property value is not an integer greater than or equal
      * to 1.
      */
     public static int getDefaultThreadCount() {
         int k = PJProperties.getPjNt();
         if (k == 0) {
             k = Runtime.getRuntime().availableProcessors();
         }
         return k;
     }
 
 // Hidden operations.
     /**
      * Do the thread-0 portion of a barrier with no barrier action. This method
      * is called by thread 0 of the parallel team.
      */
     void barrier() {
         // Get the new team barrier flag.
         int newBarrierFlag = myBarrierFlag ^ 1;
 
         // Wait until each team thread 1 .. K-1 has switched to the new
         // barrier flag.
         for (int i = 1; i < K; ++i) {
             ParallelTeamThread thread_i = myThread[i];
             if (thread_i.myBarrierFlag != newBarrierFlag) {
                 Spinner spinner = new Spinner();
                 while (thread_i.myBarrierFlag != newBarrierFlag) {
                     spinner.spin();
                 }
             }
         }
 
         // Switch to the new team barrier flag.
         myBarrierFlag = newBarrierFlag;
     }
 
     /**
      * Do the thread-0 portion of a barrier with a barrier action. This method
      * is called by thread 0 of the parallel team.
      *
      * @param action Barrier action.
      *
      * @exception Exception Thrown if the <code>action</code>'s <code>run()</code>
      * method throws an exception.
      */
     void barrier(BarrierAction action)
             throws Exception {
         // Get the new team barrier flag.
         int newBarrierFlag = myBarrierFlag ^ 1;
 
         // Wait until each team thread 1 .. K-1 has switched to the new
         // barrier flag.
         for (int i = 1; i < K; ++i) {
             ParallelTeamThread thread_i = myThread[i];
             if (thread_i.myBarrierFlag != newBarrierFlag) {
                 Spinner spinner = new Spinner();
                 while (thread_i.myBarrierFlag != newBarrierFlag) {
                     spinner.spin();
                 }
             }
         }
 
         try {
             // Do the barrier action.
             action.myTeam = this;
             action.run();
         } finally {
             action.myTeam = null;
 
             // Switch to the new team barrier flag.
             myBarrierFlag = newBarrierFlag;
         }
     }
 
     /**
      * Re-throw the given object as a checked or unchecked exception. If the
      * given object is null or is not throwable, do nothing.
      */
     static void rethrow(Object exc)
             throws Exception {
         if (exc instanceof RuntimeException) {
             throw (RuntimeException) exc;
         } else if (exc instanceof Exception) {
             throw (Exception) exc;
         } else if (exc instanceof Error) {
             throw (Error) exc;
         }
     }
     
     /**
      * Kills the team's threads run() methods so that they are no longer GC roots.
      * Useful if you are repetitively constructing ParallelTeam objects, although
      * it is slightly more elegant just to keep the same ParallelTeam objects through
      * the entire execution of a program.
      *
      * @throws java.lang.Exception if any.
      */
     public void shutdown() throws Exception {
         if (isActive) {
             this.execute(new KillRegion());
             isActive = false;
         }
     }
 }