ConcurrentBag.cs

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// 
// ConcurrentBag.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;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.InteropServices;

using System.Threading;
using System.Threading.Tasks;

namespace System.Collections.Concurrent
{
    [ComVisible (false)]
    [DebuggerDisplay ("Count={Count}")]
    [DebuggerTypeProxy (typeof (CollectionDebuggerView<>))]
    public class ConcurrentBag<T> : IProducerConsumerCollection<T>, IEnumerable<T>, IEnumerable
    {
        // We store hints in a long
        long hints;

        int count;
        // The container area is where bag are added foreach thread
        ConcurrentDictionary<int, CyclicDeque<T>> container = new ConcurrentDictionary<int, CyclicDeque<T>> ();
        // The staging area is where non-empty bag are located for fast iteration
        ConcurrentDictionary<int, CyclicDeque<T>> staging = new ConcurrentDictionary<int, CyclicDeque<T>> ();
        
        public ConcurrentBag ()
        {
        }
        
        public ConcurrentBag (IEnumerable<T> collection) : this ()
        {
            foreach (T item in collection)
                Add (item);
        }
        
        public void Add (T item)
        {
            int index;
            CyclicDeque<T> bag = GetBag (out index);
            bag.PushBottom (item);
            AddHint (index);
            Interlocked.Increment (ref count);
        }

        bool IProducerConsumerCollection<T>.TryAdd (T element)
        {
            Add (element);
            return true;
        }
        
        public bool TryTake (out T result)
        {
            result = default (T);

            if (count == 0)
                return false;

            int hintIndex;
            CyclicDeque<T> bag = GetBag (out hintIndex, false);
            bool ret = true;
            
            if (bag == null || bag.PopBottom (out result) != PopResult.Succeed) {
                var self = bag;
                foreach (var other in staging) {
                    // Try to retrieve something based on a hint
                    ret = TryGetHint (out hintIndex) && (bag = container[hintIndex]).PopTop (out result) == PopResult.Succeed;

                    // We fall back to testing our slot
                    if (!ret && other.Value != self) {
                        var status = other.Value.PopTop (out result);
                        while (status == PopResult.Abort)
                            status = other.Value.PopTop (out result);
                        ret = status == PopResult.Succeed;
                        hintIndex = other.Key;
                        bag = other.Value;
                    }
                    
                    // If we found something, stop
                    if (ret)
                        break;
                }
            }

            if (ret) {
                TidyBag (hintIndex, bag);
                Interlocked.Decrement (ref count);
            }

            return ret;
        }

        public bool TryPeek (out T result)
        {
            result = default (T);

            if (count == 0)
                return false;

            int hintIndex;
            CyclicDeque<T> bag = GetBag (out hintIndex, false);
            bool ret = true;

            if (bag == null || !bag.PeekBottom (out result)) {
                var self = bag;
                foreach (var other in staging) {
                    // Try to retrieve something based on a hint
                    ret = TryGetHint (out hintIndex) && container[hintIndex].PeekTop (out result);

                    // We fall back to testing our slot
                    if (!ret && other.Value != self)
                        ret = other.Value.PeekTop (out result);

                    // If we found something, stop
                    if (ret)
                        break;
                }
            }

            return ret;
        }

        void AddHint (int index)
        {
            // We only take thread index that can be stored in 5 bits (i.e. thread ids 1-15)
            if (index > 0xF)
                return;
            var hs = hints;
            // If cas failed then we don't retry
            Interlocked.CompareExchange (ref hints, (long)(((ulong)hs) << 4 | (uint)index), (long)hs);
        }

        bool TryGetHint (out int index)
        {
            /* Funny little thing to know, since hints is a long (because CAS has no ulong overload),
             * a shift-right operation is an arithmetic shift which might set high-order right bits
             * to 1 instead of 0 if the number turns negative.
             */
            var hs = hints;
            index = 0;

            if (Interlocked.CompareExchange (ref hints, (long)(((ulong)hs) >> 4), hs) == hs)
                index = (int)(hs & 0xF);

            return index > 0;
        }
        
        public int Count {
            get {
                return count;
            }
        }
        
        public bool IsEmpty {
            get {
                return count == 0;
            }
        }
        
        object System.Collections.ICollection.SyncRoot  {
            get {
                return this;
            }
        }
        
        bool System.Collections.ICollection.IsSynchronized  {
            get {
                return true;
            }
        }
        
        IEnumerator IEnumerable.GetEnumerator ()
        {
            return GetEnumeratorInternal ();
        }
        
        public IEnumerator<T> GetEnumerator ()
        {
            return GetEnumeratorInternal ();
        }
        
        IEnumerator<T> GetEnumeratorInternal ()
        {
            foreach (var bag in container)
                foreach (T item in bag.Value.GetEnumerable ())
                    yield return item;
        }
        
        void System.Collections.ICollection.CopyTo (Array array, int index)
        {
            T[] a = array as T[];
            if (a == null)
                return;
            
            CopyTo (a, index);
        }
        
        public void CopyTo (T[] array, int index)
        {
            int c = count;
            if (array.Length < c + index)
                throw new InvalidOperationException ("Array is not big enough");
            
            CopyTo (array, index, c);
        }
        
        void CopyTo (T[] array, int index, int num)
        {
            int i = index;
            
            foreach (T item in this) {
                if (i >= num)
                    break;
                
                array[i++] = item;
            }
        }
        
        public T[] ToArray ()
        {
            int c = count;
            T[] temp = new T[c];
            
            CopyTo (temp, 0, c);
            
            return temp;
        }

        int GetIndex ()
        {
            return Thread.CurrentThread.ManagedThreadId;
        }
                
        CyclicDeque<T> GetBag (out int index, bool createBag = true)
        {
            index = GetIndex ();
            CyclicDeque<T> value;
            if (container.TryGetValue (index, out value))
                return value;

            var bag = createBag ? container.GetOrAdd (index, new CyclicDeque<T> ()) : null;
            if (bag != null)
                staging.TryAdd (index, bag);
            return bag;
        }

        void TidyBag (int index, CyclicDeque<T> bag)
        {
            if (bag != null && bag.IsEmpty) {
                if (staging.TryRemove (index, out bag) && !bag.IsEmpty)
                    staging.TryAdd (index, bag);
            }
        }
    }
}
#endif