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                 public ConcurrentQueue ()
  52                 {
  53                         tail = head;
  54                 }
  55
  56                 public ConcurrentQueue (IEnumerable<T> collection): this()
  57                 {
  58                         foreach (T item in collection)
  59                                 Enqueue (item);
  60                 }
  61
  62                 public void Enqueue (T item)
  63                 {
  64                         Node node  = new Node ();
  65                         node.Value = item;
  66
  67                         Node oldTail = null;
  68                         Node oldNext = null;
  69
  70                         bool update = false;
  71                         while (!update) {
  72                                 oldTail = tail;
  73                                 oldNext = oldTail.Next;
  74
  75                                 // Did tail was already updated ?
  76                                 if (tail == oldTail) {
  77                                         if (oldNext == null) {
  78                                                 // The place is for us
  79                                                 update = Interlocked.CompareExchange (ref tail.Next, node, null) == null;
  80                                         } else {
  81                                                 // another Thread already used the place so give him a hand by putting tail where it should be
  82                                                 Interlocked.CompareExchange (ref tail, oldNext, oldTail);
  83                                         }
  84                                 }
  85                         }
  86                         // 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
  87                         Interlocked.CompareExchange (ref tail, node, oldTail);
  88
  89                         Interlocked.Increment (ref count);
  90                 }
  91
  92                 bool IProducerConsumerCollection<T>.TryAdd (T item)
  93                 {
  94                         Enqueue (item);
  95                         return true;
  96                 }
  97
  98                 public bool TryDequeue (out T result)
  99                 {
 100                         result = default (T);
 101                         bool advanced = false;
 102
 103                         while (!advanced) {
 104                                 Node oldHead = head;
 105                                 Node oldTail = tail;
 106                                 Node oldNext = oldHead.Next;
 107
 108                                 if (oldHead == head) {
 109                                         // Empty case ?
 110                                         if (oldHead == oldTail) {
 111                                                 // This should be false then
 112                                                 if (oldNext != null) {
 113                                                         // If not then the linked list is mal formed, update tail
 114                                                         Interlocked.CompareExchange (ref tail, oldNext, oldTail);
 115                                                 }
 116                                                 result = default (T);
 117                                                 return false;
 118                                         } else {
 119                                                 result = oldNext.Value;
 120                                                 advanced = Interlocked.CompareExchange (ref head, oldNext, oldHead) == oldHead;
 121                                         }
 122                                 }
 123                         }
 124
 125                         Interlocked.Decrement (ref count);
 126
 127                         return true;
 128                 }
 129
 130                 public bool TryPeek (out T result)
 131                 {
 132                         if (IsEmpty) {
 133                                 result = default (T);
 134                                 return false;
 135                         }
 136
 137                         Node first = head.Next;
 138                         result = first.Value;
 139                         return true;
 140                 }
 141
 142                 internal void Clear ()
 143                 {
 144                         count = 0;
 145                         tail = head = new Node ();
 146                 }
 147
 148                 IEnumerator IEnumerable.GetEnumerator ()
 149                 {
 150                         return (IEnumerator)InternalGetEnumerator ();
 151                 }
 152
 153                 public IEnumerator<T> GetEnumerator ()
 154                 {
 155                         return InternalGetEnumerator ();
 156                 }
 157
 158                 IEnumerator<T> InternalGetEnumerator ()
 159                 {
 160                         Node my_head = head;
 161                         while ((my_head = my_head.Next) != null) {
 162                                 yield return my_head.Value;
 163                         }
 164                 }
 165
 166                 void ICollection.CopyTo (Array array, int index)
 167                 {
 168                         T[] dest = array as T[];
 169                         if (dest == null)
 170                                 return;
 171                         CopyTo (dest, index);
 172                 }
 173
 174                 public void CopyTo (T[] array, int index)
 175                 {
 176                         IEnumerator<T> e = InternalGetEnumerator ();
 177                         int i = index;
 178                         while (e.MoveNext ()) {
 179                                 array [i++] = e.Current;
 180                         }
 181                 }
 182
 183                 public T[] ToArray ()
 184                 {
 185                         T[] dest = new T [count];
 186                         CopyTo (dest, 0);
 187                         return dest;
 188                 }
 189
 190                 bool ICollection.IsSynchronized {
 191                         get { return true; }
 192                 }
 193
 194                 bool IProducerConsumerCollection<T>.TryTake (out T item)
 195                 {
 196                         return TryDequeue (out item);
 197                 }
 198
 199                 object syncRoot = new object();
 200                 object ICollection.SyncRoot {
 201                         get { return syncRoot; }
 202                 }
 203
 204                 public int Count {
 205                         get {
 206                                 return count;
 207                         }
 208                 }
 209
 210                 public bool IsEmpty {
 211                         get {
 212                                 return count == 0;
 213                         }
 214                 }
 215         }
 216 }
 217 #endif