SimpleConcurrentBag.cs

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// 
// SimpleConcurrentBag.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;

namespace System.Threading.Tasks
{

    internal class SimpleConcurrentBag<T>
    {
        readonly IConcurrentDeque<T>[] deques;
        readonly bool unique;
        int index = -1;
        
        [ThreadStatic]
        int stealIndex;
        
        public SimpleConcurrentBag (int num)
        {
            deques = new CyclicDeque<T>[num];
            for (int i = 0; i < deques.Length; i++) {
                deques[i] = new CyclicDeque<T> ();
            }
            unique = num <= 1;
        }
        
        public int GetNextIndex ()
        {
            return Interlocked.Increment (ref index);
        }
        
        public bool TryTake (int index, out T value)
        {
            value = default (T);
            
            return deques[index].PopBottom (out value) == PopResult.Succeed;
        }
        
        public bool TrySteal (int index, out T value)
        {
            value = default (T);
            
            if (unique)
                return false;
            
            const int roundThreshold = 3;
            
            for (int round = 0; round < roundThreshold; ++round) {
                if (stealIndex == index)
                    stealIndex = (stealIndex + 1) % deques.Length;
            
                if (deques[(stealIndex = (stealIndex + 1) % deques.Length)].PopTop (out value) == PopResult.Succeed)
                    return true;
            }
            
            return false;
        }
        
        public void Add (int index, T value)
        {
            deques[index].PushBottom (value);
        }
    }
}
#endif