mono/mcs/class/corlib/System.Collections.Concurrent/ConcurrentQueue.cs

// ConcurrentQueue.cs
//
// Copyright (c) 2008 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 || BOOTSTRAP_NET_4_0

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

namespace System.Collections.Concurrent
{
	
	public class ConcurrentQueue<T> : IProducerConsumerCollection<T>, IEnumerable<T>, ICollection,
	                                  IEnumerable
	{
		class Node
		{
			public T Value;
			public Node Next;
		}
		
		Node head = new Node ();
		Node tail;
		int count;

		public ConcurrentQueue ()
		{
			tail = head;
		}
		
		public ConcurrentQueue (IEnumerable<T> enumerable): this()
		{
			foreach (T item in enumerable)
				Enqueue (item);
		}
		
		public void Enqueue (T item)
		{
			Node node  = new Node ();
			node.Value = item;
			
			Node oldTail = null;
			Node oldNext = null;
			
			bool update = false;
			while (!update) {
				oldTail = tail;
				oldNext = oldTail.Next;
				
				// Did tail was already updated ?
				if (tail == oldTail) {
					if (oldNext == null) {
						// The place is for us
						update = Interlocked.CompareExchange (ref tail.Next, node, null) == null;
					} else {
						// another Thread already used the place so give him a hand by putting tail where it should be
						Interlocked.CompareExchange (ref tail, oldNext, oldTail);
					}
				}
			}
			// At this point we added correctly our node, now we have to update tail. If it fails then it will be done by another thread
			Interlocked.CompareExchange (ref tail, node, oldTail);

			Interlocked.Increment (ref count);
		}
		
		bool IProducerConsumerCollection<T>.TryAdd (T item)
		{
			Enqueue (item);
			return true;
		}

		public bool TryDequeue (out T value)
		{
			value = default (T);
			bool advanced = false;

			while (!advanced) {
				Node oldHead = head;
				Node oldTail = tail;
				Node oldNext = oldHead.Next;
				
				if (oldHead == head) {
					// Empty case ?
					if (oldHead == oldTail) {	
						// This should be false then
						if (oldNext != null) {
							// If not then the linked list is mal formed, update tail
							Interlocked.CompareExchange (ref tail, oldNext, oldTail);
						}
						value = default (T);
						return false;
					} else {
						value = oldNext.Value;
						advanced = Interlocked.CompareExchange (ref head, oldNext, oldHead) == oldHead;
					}
				}
			}

			Interlocked.Decrement (ref count);

			return true;
		}
		
		public bool TryPeek (out T value)
		{
			if (IsEmpty) {
				value = default (T);
				return false;
			}
			
			Node first = head.Next;
			value = first.Value;
			return true;
		}
		
		internal void Clear ()
		{
			count = 0;
			tail = head = new Node ();
		}
		
		IEnumerator IEnumerable.GetEnumerator ()
		{
			return (IEnumerator)InternalGetEnumerator ();
		}
		
		public IEnumerator<T> GetEnumerator ()
		{
			return InternalGetEnumerator ();
		}
		
		IEnumerator<T> InternalGetEnumerator ()
		{
			Node my_head = head;
			while ((my_head = my_head.Next) != null) {
				yield return my_head.Value;
			}
		}
		
		void ICollection.CopyTo (Array array, int index)
		{
			T[] dest = array as T[];
			if (dest == null)
				return;
			CopyTo (dest, index);
		}
		
		public void CopyTo (T[] dest, int index)
		{
			IEnumerator<T> e = InternalGetEnumerator ();
			int i = index;
			while (e.MoveNext ()) {
				dest [i++] = e.Current;
			}
		}
		
		public T[] ToArray ()
		{
			T[] dest = new T [count];
			CopyTo (dest, 0);
			return dest;
		}
		
		bool ICollection.IsSynchronized {
			get { return true; }
		}

		bool IProducerConsumerCollection<T>.TryTake (out T item)
		{
			return TryDequeue (out item);
		}
		
		object syncRoot = new object();
		object ICollection.SyncRoot {
			get { return syncRoot; }
		}
		
		public int Count {
			get {
				return count;
			}
		}
		
		public bool IsEmpty {
			get {
				return count == 0;
			}
		}
	}
}
#endif