ListPartitioner.cs

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// 
// ListPartitioner.cs
//  
// Author:
//       Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
// 
// Copyright (c) 2009 Jérémie "Garuma" Laval
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#if NET_4_0

using System;
using System.Threading;
using System.Collections.Generic;
using System.Runtime.InteropServices;

namespace System.Collections.Concurrent.Partitioners
{
    // Represent a Range partitioner
    internal class ListPartitioner<T> : OrderablePartitioner<T>
    {
        IList<T> source;
        
        public ListPartitioner (IList<T> source) : base (true, true, true)
        {
            this.source = source;
        }
        
        public override IList<IEnumerator<KeyValuePair<long, T>>> GetOrderablePartitions (int partitionCount)
        {
            if (partitionCount <= 0)
                throw new ArgumentOutOfRangeException ("partitionCount");
            
            IEnumerator<KeyValuePair<long, T>>[] enumerators
                = new IEnumerator<KeyValuePair<long, T>>[partitionCount];
            
            int count = source.Count / partitionCount;
            int extra = 0;

            if (source.Count < partitionCount) {
                count = 1;
            } else {
                extra = source.Count % partitionCount;
                if (extra > 0)
                    ++count;
            }

            int currentIndex = 0;

            Range[] ranges = new Range[enumerators.Length];
            for (int i = 0; i < ranges.Length; i++) {
                ranges[i] = new Range (currentIndex,
                                       currentIndex + count);
                currentIndex += count;
                if (--extra == 0)
                    --count;
            }
            
            for (int i = 0; i < enumerators.Length; i++) {
                enumerators[i] = GetEnumeratorForRange (ranges, i);
            }
            
            return enumerators;
        }

        class Range
        {
            public int Actual;
            public readonly int LastIndex;

            public Range (int frm, int lastIndex)
            {
                Actual = frm;
                LastIndex = lastIndex;
            }
        }
        
        IEnumerator<KeyValuePair<long, T>> GetEnumeratorForRange (Range[] ranges, int workerIndex)
        {
            if (ranges[workerIndex].Actual >= source.Count)
              return GetEmpty ();
            
            return GetEnumeratorForRangeInternal (ranges, workerIndex);
        }

        IEnumerator<KeyValuePair<long, T>> GetEmpty ()
        {
            yield break;
        }
        
        IEnumerator<KeyValuePair<long, T>> GetEnumeratorForRangeInternal (Range[] ranges, int workerIndex)
        {
            Range range = ranges[workerIndex];
            int lastIndex = range.LastIndex;
            int index = range.Actual;

            for (int i = index; i < lastIndex; i = ++range.Actual) {
                yield return new KeyValuePair<long, T> (i, source[i]);
            }
        }
    }
}
#endif