// ******************************************************************************
   //
   // Title:       Force Field X.
   // Description: Force Field X - Software for Molecular Biophysics.
   // Copyright:   Copyright (c) Michael J. Schnieders 2001-2025.
   //
   // This file is part of Force Field X.
   //
   // Force Field X is free software; you can redistribute it and/or modify it
  // under the terms of the GNU General Public License version 3 as published by
  // the Free Software Foundation.
  //
  // Force Field X 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.
  //
  // You should have received a copy of the GNU General Public License along with
  // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
  // Place, Suite 330, Boston, MA 02111-1307 USA
  //
  // 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.
  //
  // ******************************************************************************
  package ffx.numerics.atomic;
  
  import edu.rit.pj.IntegerForLoop;
  import edu.rit.pj.ParallelRegion;
  import edu.rit.pj.ParallelTeam;
  import java.util.concurrent.atomic.DoubleAdder;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  /**
   * AdderDoubleArray implements the AtomicDoubleArray interface using an array of <code>
   * java.util.concurrent.atomic.DoubleAdder</code>.
   *
   * @author Michael J. Schnieders
   * @since 1.0
   */
  public class AdderDoubleArray implements AtomicDoubleArray {
  
    private static final Logger logger = Logger.getLogger(AdderDoubleArray.class.getName());
  
    /**
     * The zero value used for resetting the array.
     */
    private static final double ZERO_VALUE = 0.0;
  
    /**
     * Atomic operations are handled by an array of DoubleAdder instances.
     */
    private DoubleAdder[] doubleAdders;
  
    /**
     * The size of the array.
     */
    private int arraySize;
  
    /**
     * Construct an AdderDoubleArray.
     *
     * @param size Size of the array.
     */
    public AdderDoubleArray(int size) {
      this.arraySize = size;
      this.doubleAdders = createDoubleAdders(size);
    }
  
    /**
     * Creates the internal array of DoubleAdder instances.
     *
     * @param size The size of the array.
     * @return An array of initialized DoubleAdder objects.
     */
    private DoubleAdder[] createDoubleAdders(int size) {
      DoubleAdder[] adders = new DoubleAdder[size];
      for (int i = 0; i < size; i++) {
        adders[i] = new DoubleAdder();
      }
      return adders;
    }
  
    /**
     * {@inheritDoc}
     */
   @Override
   public void add(int threadID, int index, double value) {
     doubleAdders[index].add(value);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void alloc(int size) {
     this.arraySize = size;
     if (doubleAdders.length < size) {
       this.doubleAdders = createDoubleAdders(size);
     }
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public double get(int index) {
     return doubleAdders[index].sum();
   }
 
   /**
    * The AtomicDoubleArray handles the reduction automatically, so this method does nothing.
    */
   @Override
   public void reduce(int lb, int ub) {
     // Nothing to do.
   }
 
   /**
    * The AtomicDoubleArray handles the reduction automatically, so this method does nothing.
    */
   @Override
   public void reduce(ParallelTeam parallelTeam, int lb, int ub) {
     // Nothing to do.
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void reset(int threadID, int lb, int ub) {
     resetRange(lb, ub);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void reset(ParallelTeam parallelTeam, int lb, int ub) {
     try {
       parallelTeam.execute(
           new ParallelRegion() {
             @Override
             public void run() throws Exception {
               execute(lb, ub,
                   new IntegerForLoop() {
                     @Override
                     public void run(int first, int last) {
                       resetRange(first, last);
                     }
                   });
             }
           });
     } catch (Exception e) {
       logger.log(Level.WARNING, "Exception resetting an AdderDoubleArray", e);
     }
   }
 
   /**
    * Resets an inclusive range of DoubleAdders in the array.
    */
   private void resetRange(int start, int end) {
     for (int i = start; i <= end; i++) {
       resetAdder(doubleAdders[i]);
     }
   }
 
   /**
    * Resets a single DoubleAdder to the zero value.
    *
    * @param adder The DoubleAdder to reset.
    */
   private void resetAdder(DoubleAdder adder) {
     adder.reset();
     adder.add(ZERO_VALUE);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void scale(int threadID, int index, double value) {
     double current = doubleAdders[index].sumThenReset();
     doubleAdders[index].add(current * value);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void set(int threadID, int index, double value) {
     resetAdder(doubleAdders[index]);
     doubleAdders[index].add(value);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public int size() {
     return arraySize;
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void sub(int threadID, int index, double value) {
     doubleAdders[index].add(-value);
   }
 }