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

   1 // ConcurrentQueue.cs
   2 //
   3 // Copyright (c) 2008 Jérémie "Garuma" Laval
   4 //
   5 // Permission is hereby granted, free of charge, to any person obtaining a copy
   6 // of this software and associated documentation files (the "Software"), to deal
   7 // in the Software without restriction, including without limitation the rights
   8 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   9 // copies of the Software, and to permit persons to whom the Software is
  10 // furnished to do so, subject to the following conditions:
  11 //
  12 // The above copyright notice and this permission notice shall be included in
  13 // all copies or substantial portions of the Software.
  14 //
  15 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  18 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  20 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  21 // THE SOFTWARE.
  22 //
  23 //
  24
  25 #if NET_4_0 || MOBILE
  26
  27 using System;
  28 using System.Threading;
  29 using System.Collections;
  30 using System.Collections.Generic;
  31 using System.Runtime.Serialization;
  32
  33 namespace System.Collections.Concurrent
  34 {
  35
  36         [System.Diagnostics.DebuggerDisplay ("Count={Count}")]
  37         [System.Diagnostics.DebuggerTypeProxy (typeof (CollectionDebuggerView<>))]
  38         public class ConcurrentQueue<T> : IProducerConsumerCollection<T>, IEnumerable<T>, ICollection,
  39                                           IEnumerable
  40         {
  41                 class Node
  42                 {
  43                         public T Value;
  44                         public Node Next;
  45                 }
  46
  47                 Node head = new Node ();
  48                 Node tail;
  49                 int count;
  50
  51                 class NodeObjectPool : ObjectPool<Node> {
  52                         protected override Node Creator ()
  53                         {
  54                                 return new Node ();
  55                         }
  56                 }
  57                 static readonly NodeObjectPool pool = new NodeObjectPool ();
  58
  59                 static Node ZeroOut (Node node)
  60                 {
  61                         node.Value = default(T);
  62                         node.Next = null;
  63                         return node;
  64                 }
  65
  66                 public ConcurrentQueue ()
  67                 {
  68                         tail = head;
  69                 }
  70
  71                 public ConcurrentQueue (IEnumerable<T> collection): this()
  72                 {
  73                         foreach (T item in collection)
  74                                 Enqueue (item);
  75                 }
  76
  77                 public void Enqueue (T item)
  78                 {
  79                         Node node = pool.Take ();
  80                         node.Value = item;
  81
  82                         Node oldTail = null;
  83                         Node oldNext = null;
  84
  85                         bool update = false;
  86                         while (!update) {
  87                                 oldTail = tail;
  88                                 oldNext = oldTail.Next;
  89
  90                                 // Did tail was already updated ?
  91                                 if (tail == oldTail) {
  92                                         if (oldNext == null) {
  93                                                 // The place is for us
  94                                                 update = Interlocked.CompareExchange (ref tail.Next, node, null) == null;
  95                                         } else {
  96                                                 // another Thread already used the place so give him a hand by putting tail where it should be
  97                                                 Interlocked.CompareExchange (ref tail, oldNext, oldTail);
  98                                         }
  99                                 }
 100                         }
 101                         // 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
 102                         Interlocked.CompareExchange (ref tail, node, oldTail);
 103
 104                         Interlocked.Increment (ref count);
 105                 }
 106
 107                 bool IProducerConsumerCollection<T>.TryAdd (T item)
 108                 {
 109                         Enqueue (item);
 110                         return true;
 111                 }
 112
 113                 public bool TryDequeue (out T result)
 114                 {
 115                         result = default (T);
 116                         bool advanced = false;
 117
 118                         while (!advanced) {
 119                                 Node oldHead = head;
 120                                 Node oldTail = tail;
 121                                 Node oldNext = oldHead.Next;
 122
 123                                 if (oldHead == head) {
 124                                         // Empty case ?
 125                                         if (oldHead == oldTail) {
 126                                                 // This should be false then
 127                                                 if (oldNext != null) {
 128                                                         // If not then the linked list is mal formed, update tail
 129                                                         Interlocked.CompareExchange (ref tail, oldNext, oldTail);
 130                                                 }
 131                                                 result = default (T);
 132                                                 return false;
 133                                         } else {
 134                                                 result = oldNext.Value;
 135                                                 advanced = Interlocked.CompareExchange (ref head, oldNext, oldHead) == oldHead;
 136                                                 if (advanced)
 137                                                         pool.Release (ZeroOut (oldHead));
 138                                         }
 139                                 }
 140                         }
 141
 142                         Interlocked.Decrement (ref count);
 143
 144                         return true;
 145                 }
 146
 147                 public bool TryPeek (out T result)
 148                 {
 149                         if (IsEmpty) {
 150                                 result = default (T);
 151                                 return false;
 152                         }
 153
 154                         Node first = head.Next;
 155                         result = first.Value;
 156                         return true;
 157                 }
 158
 159                 internal void Clear ()
 160                 {
 161                         count = 0;
 162                         tail = head = new Node ();
 163                 }
 164
 165                 IEnumerator IEnumerable.GetEnumerator ()
 166                 {
 167                         return (IEnumerator)InternalGetEnumerator ();
 168                 }
 169
 170                 public IEnumerator<T> GetEnumerator ()
 171                 {
 172                         return InternalGetEnumerator ();
 173                 }
 174
 175                 IEnumerator<T> InternalGetEnumerator ()
 176                 {
 177                         Node my_head = head;
 178                         while ((my_head = my_head.Next) != null) {
 179                                 yield return my_head.Value;
 180                         }
 181                 }
 182
 183                 void ICollection.CopyTo (Array array, int index)
 184                 {
 185                         T[] dest = array as T[];
 186                         if (dest == null)
 187                                 return;
 188                         CopyTo (dest, index);
 189                 }
 190
 191                 public void CopyTo (T[] array, int index)
 192                 {
 193                         IEnumerator<T> e = InternalGetEnumerator ();
 194                         int i = index;
 195                         while (e.MoveNext ()) {
 196                                 array [i++] = e.Current;
 197                         }
 198                 }
 199
 200                 public T[] ToArray ()
 201                 {
 202                         T[] dest = new T [count];
 203                         CopyTo (dest, 0);
 204                         return dest;
 205                 }
 206
 207                 bool ICollection.IsSynchronized {
 208                         get { return true; }
 209                 }
 210
 211                 bool IProducerConsumerCollection<T>.TryTake (out T item)
 212                 {
 213                         return TryDequeue (out item);
 214                 }
 215
 216                 object syncRoot = new object();
 217                 object ICollection.SyncRoot {
 218                         get { return syncRoot; }
 219                 }
 220
 221                 public int Count {
 222                         get {
 223                                 return count;
 224                         }
 225                 }
 226
 227                 public bool IsEmpty {
 228                         get {
 229                                 return count == 0;
 230                         }
 231                 }
 232         }
 233 }
 234 #endif