CyclicDeque.cs

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// 
// CyclicDeque.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.Collections.Generic;
using System.Threading;

#if INSIDE_MONO_PARALLEL
namespace Mono.Threading.Tasks
#else
namespace System.Threading.Tasks
#endif
{
#if INSIDE_MONO_PARALLEL
    public
#endif
    class CyclicDeque<T> : IConcurrentDeque<T>
    {
        const int BaseSize = 11;
        
        long bottom;
        long top;
        long upperBound;
        CircularArray<T> array = new CircularArray<T> (BaseSize);
        
        public void PushBottom (T obj)
        {
            /* Read is implemented as a simple load operation on 64bits
             * so no need to make the distinction ourselves
             */
            long b = Interlocked.Read (ref bottom);
            var a = array;
            
            // Take care of growing
            if (b - upperBound >= a.Size - 1) {
                upperBound = Interlocked.Read (ref top);
                a = a.Grow (b, upperBound);
                array = a;
            }
            
            // Register the new value
            a.segment[b % a.size] = obj;
            Interlocked.Increment (ref bottom);
        }
        
        public PopResult PopBottom (out T obj)
        {
            obj = default (T);
            
            long b = Interlocked.Decrement (ref bottom);
            var a = array;
            long t = Interlocked.Read (ref top);
            long size = b - t;
            
            if (size < 0) {
                // Set bottom to t
                Interlocked.Add (ref bottom, t - b);
                return PopResult.Empty;
            }
            
            obj = a.segment[b % a.size];
            if (size > 0)
                return PopResult.Succeed;
            Interlocked.Add (ref bottom, t + 1 - b);
            
            if (Interlocked.CompareExchange (ref top, t + 1, t) != t)
                return PopResult.Empty;
            
            return PopResult.Succeed;
        }

        public bool PeekBottom (out T obj)
        {
            obj = default (T);

            long b = Interlocked.Decrement (ref bottom);
            var a = array;
            long t = Interlocked.Read (ref top);
            long size = b - t;

            if (size < 0)
                return false;

            obj = a.segment[b % a.size];
            return true;
        }
        
        public PopResult PopTop (out T obj)
        {
            obj = default (T);
            
            long t = Interlocked.Read (ref top);
            long b = Interlocked.Read (ref bottom);
            
            if (b - t <= 0)
                return PopResult.Empty;
            
            if (Interlocked.CompareExchange (ref top, t + 1, t) != t)
                return PopResult.Abort;
            
            var a = array;
            obj = a.segment[t % a.size];
            
            return PopResult.Succeed;
        }

        internal bool PeekTop (out T obj)
        {
            obj = default (T);

            long t = Interlocked.Read (ref top);
            long b = Interlocked.Read (ref bottom);

            if (b - t <= 0)
                return false;

            var a = array;
            obj = a.segment[t % a.size];

            return true;
        }
        
        public IEnumerable<T> GetEnumerable ()
        {
            var a = array;
            return a.GetEnumerable (bottom, ref top);
        }

        public bool IsEmpty {
            get {
                long t = Interlocked.Read (ref top);
                long b = Interlocked.Read (ref bottom);
                return b - t <= 0;
            }
        }
    }
    
    internal class CircularArray<T>
    {
        readonly int baseSize;
        public readonly int size;
        public readonly T[] segment;
        
        public CircularArray (int baseSize)
        {
            this.baseSize = baseSize;
            this.size = 1 << baseSize;
            this.segment = new T[size];
        }
        
        public long Size {
            get {
                return size;
            }
        }
        
        public T this[long index] {
            get {
                return segment[index % size];
            }
            set {
                segment[index % size] = value;
            }
        }
        
        public CircularArray<T> Grow (long bottom, long top)
        {
            var grow = new CircularArray<T> (baseSize + 1);
            
            for (long i = top; i < bottom; i++) {
                grow.segment[i] = segment[i % size];
            }
            
            return grow;
        }
        
        public IEnumerable<T> GetEnumerable (long bottom, ref long top)
        {
            long instantTop = top;
            T[] slice = new T[bottom - instantTop];
            int destIndex = -1;
            for (long i = instantTop; i < bottom; i++)
                slice[++destIndex] = segment[i % size];

            return RealGetEnumerable (slice, bottom, top, instantTop);
        }

        IEnumerable<T> RealGetEnumerable (T[] slice, long bottom, long realTop, long initialTop)
        {
            int destIndex = (int)(realTop - initialTop - 1);
            for (long i = realTop; i < bottom; ++i)
                yield return slice[++destIndex];
        }
    }
}
#endif