package org.apidesign.reentrant;

 import java.util.Collection;

 import java.util.concurrent.atomic.AtomicInteger;

 public class CriticalSectionReentrantImmutable<T extends Comparable<T>> implements CriticalSection<T> {

     private ImmutableData<T> data = new ImmutableData<T>();

     public void assignPilot(T pilot) {

         data = data.newPilot(pilot);

     }

     // BEGIN: reentrant.merge.immutable

     public int sumBigger(Collection<T> args) {

         for (;;) {

             ImmutableData<T> previous;

             synchronized (this) {

                 previous = this.data;

             }

             int[] ret = { 0 };

             ImmutableData<T> now = doCriticalSection(args, previous, ret);

             synchronized (this) {

                 // if there was no parallel or reentrant change, 

                 // apply and return. Otherwise try once more.

                 if (previous == this.data) {

                     this.data = now;

                     return ret[0];

                 }

             }

         }

     }

     // END: reentrant.merge.immutable

     private ImmutableData<T> doCriticalSection(Collection<T> args, ImmutableData<T> data, int[] result) {

         result[0] = 0;

         for (T cmp : args) {

             if (data.pilot.compareTo(cmp) < 0) {

                 result[0]++;

             }

         }

         return data.newCnt(data.cnt + result[0]);

     }

     public int getCount() {

         return data.cnt;

     }

     private static final class ImmutableData<T> {

         final T pilot;

         final int cnt;

         public ImmutableData() {

             pilot = null;

             cnt = 0;

         }

         private ImmutableData(T pilot, int cnt) {

             this.pilot = pilot;

             this.cnt = cnt;

         }

         public ImmutableData<T> newPilot(T pilot) {

             return new ImmutableData(pilot, this.cnt);

         }

         public ImmutableData<T> newCnt(int cnt) {

             return new ImmutableData(this.pilot, cnt);

         }

     }

 }