EnumerablePartitioner.cs

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// 
// EnumerablePartitioner.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 || UNITY_5_3_OR_NEWER

using System;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;

namespace System.Collections.Concurrent.Partitioners
{
    // Represent a chunk partitioner
    internal class EnumerablePartitioner<T> : OrderablePartitioner<T>
    {
        IEnumerable<T> source;
        
        const int InitialPartitionSize = 1;
        const int PartitionMultiplier = 2;
        
        int initialPartitionSize;
        int partitionMultiplier;

        public EnumerablePartitioner (IEnumerable<T> source)
            : this (source, InitialPartitionSize, PartitionMultiplier)
        {

        }
        
        // This is used to get striped partitionning (for Take and Skip for instance
        public EnumerablePartitioner (IEnumerable<T> source, int initialPartitionSize, int partitionMultiplier)
             : base (true, false, true)
        {
            this.source = source;
            this.initialPartitionSize = initialPartitionSize;
            this.partitionMultiplier = partitionMultiplier;
        }
        
        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];

            PartitionerState state = new PartitionerState ();
            IEnumerator<T> src = source.GetEnumerator ();
            bool isSimple = initialPartitionSize == 1 && partitionMultiplier == 1;

            for (int i = 0; i < enumerators.Length; i++) {
                enumerators[i] = isSimple ? GetPartitionEnumeratorSimple (src, state, i == enumerators.Length - 1) : GetPartitionEnumerator (src, state);
            }
            
            return enumerators;
        }

        // This partitioner that is simpler than the general case (don't use a list) is called in the case
        // of initialPartitionSize == partitionMultiplier == 1
        IEnumerator<KeyValuePair<long, T>> GetPartitionEnumeratorSimple (IEnumerator<T> src,
                                                                         PartitionerState state,
                                                                         bool last)
        {
            long index = -1;
            var value = default (T);

            try {
                do {
                    lock (state.SyncLock) {
                        if (state.Finished)
                            break;
                        if (state.Finished = !src.MoveNext ())
                            break;

                        index = state.Index++;
                        value = src.Current;
                    }

                    yield return new KeyValuePair<long, T> (index, value);
                } while (!state.Finished);
            } finally {
                if (last)
                    src.Dispose ();
            }
        }
        
        IEnumerator<KeyValuePair<long, T>> GetPartitionEnumerator (IEnumerator<T> src, PartitionerState state)
        {
            int count = initialPartitionSize;
            List<T> list = new List<T> ();
            
            while (!state.Finished) {
                list.Clear ();
                long ind = -1;
                
                lock (state.SyncLock) {
                    if (state.Finished)
                        break;

                    ind = state.Index;
                    
                    for (int i = 0; i < count; i++) {
                        if (state.Finished = !src.MoveNext ()) {
                            if (list.Count == 0)
                                yield break;
                            else
                                break;
                        }
                        
                        list.Add (src.Current);
                        state.Index++;
                    }                   
                }
                
                for (int i = 0; i < list.Count; i++)
                    yield return new KeyValuePair<long, T> (ind + i, list[i]);
                
                count *= partitionMultiplier;
            }
        }

        class PartitionerState
        {
            public bool Finished;
            public long Index = 0;
            public readonly object SyncLock = new object ();
        }
    }
}
#endif