mcs/class/corlib/System.Threading.Tasks/CyclicDeque.cs

   1 //
   2 // CyclicDeque.cs
   3 //
   4 // Author:
   5 //       Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
   6 //
   7 // Copyright (c) 2009 Jérémie "Garuma" Laval
   8 //
   9 // Permission is hereby granted, free of charge, to any person obtaining a copy
  10 // of this software and associated documentation files (the "Software"), to deal
  11 // in the Software without restriction, including without limitation the rights
  12 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  13 // copies of the Software, and to permit persons to whom the Software is
  14 // furnished to do so, subject to the following conditions:
  15 //
  16 // The above copyright notice and this permission notice shall be included in
  17 // all copies or substantial portions of the Software.
  18 //
  19 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  22 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  23 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  24 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  25 // THE SOFTWARE.
  26
  27 #if NET_4_0 || MOBILE
  28
  29 using System;
  30 using System.Collections.Generic;
  31 using System.Threading;
  32
  33 #if INSIDE_MONO_PARALLEL
  34 namespace Mono.Threading.Tasks
  35 #else
  36 namespace System.Threading.Tasks
  37 #endif
  38 {
  39 #if INSIDE_MONO_PARALLEL
  40         public
  41 #endif
  42         enum PopResult  {
  43                 Succeed,
  44                 Empty,
  45                 Abort
  46         }
  47
  48 #if INSIDE_MONO_PARALLEL
  49         public
  50 #endif
  51         interface IConcurrentDeque<T>
  52         {
  53                 void PushBottom (T obj);
  54                 PopResult PopBottom (out T obj);
  55                 PopResult PopTop (out T obj);
  56                 IEnumerable<T> GetEnumerable ();
  57         }
  58
  59 #if INSIDE_MONO_PARALLEL
  60         public
  61 #endif
  62         class CyclicDeque<T> : IConcurrentDeque<T>
  63         {
  64                 const int BaseSize = 11;
  65
  66                 long bottom;
  67                 long top;
  68                 long upperBound;
  69                 CircularArray<T> array = new CircularArray<T> (BaseSize);
  70
  71                 public void PushBottom (T obj)
  72                 {
  73                         /* Read is implemented as a simple load operation on 64bits
  74                          * so no need to make the distinction ourselves
  75                          */
  76                         long b = Interlocked.Read (ref bottom);
  77                         var a = array;
  78
  79                         // Take care of growing
  80                         if (b - upperBound >= a.Size - 1) {
  81                                 upperBound = Interlocked.Read (ref top);
  82                                 a = a.Grow (b, upperBound);
  83                                 array = a;
  84                         }
  85
  86                         // Register the new value
  87                         a.segment[b % a.size] = obj;
  88                         Interlocked.Increment (ref bottom);
  89                 }
  90
  91                 public PopResult PopBottom (out T obj)
  92                 {
  93                         obj = default (T);
  94
  95                         long b = Interlocked.Decrement (ref bottom);
  96                         var a = array;
  97                         long t = Interlocked.Read (ref top);
  98                         long size = b - t;
  99
 100                         if (size < 0) {
 101                                 // Set bottom to t
 102                                 Interlocked.Add (ref bottom, t - b);
 103                                 return PopResult.Empty;
 104                         }
 105
 106                         obj = a.segment[b % a.size];
 107                         if (size > 0)
 108                                 return PopResult.Succeed;
 109                         Interlocked.Add (ref bottom, t + 1 - b);
 110
 111                         if (Interlocked.CompareExchange (ref top, t + 1, t) != t)
 112                                 return PopResult.Empty;
 113
 114                         return PopResult.Succeed;
 115                 }
 116
 117                 public PopResult PopTop (out T obj)
 118                 {
 119                         obj = default (T);
 120
 121                         long t = Interlocked.Read (ref top);
 122                         long b = Interlocked.Read (ref bottom);
 123
 124                         if (b - t <= 0)
 125                                 return PopResult.Empty;
 126
 127                         if (Interlocked.CompareExchange (ref top, t + 1, t) != t)
 128                                 return PopResult.Abort;
 129
 130                         var a = array;
 131                         obj = a.segment[t % a.size];
 132
 133                         return PopResult.Succeed;
 134                 }
 135
 136                 public IEnumerable<T> GetEnumerable ()
 137                 {
 138                         var a = array;
 139                         return a.GetEnumerable (bottom, ref top);
 140                 }
 141         }
 142
 143         internal class CircularArray<T>
 144         {
 145                 readonly int baseSize;
 146                 public readonly int size;
 147                 public readonly T[] segment;
 148
 149                 public CircularArray (int baseSize)
 150                 {
 151                         this.baseSize = baseSize;
 152                         this.size = 1 << baseSize;
 153                         this.segment = new T[size];
 154                 }
 155
 156                 public long Size {
 157                         get {
 158                                 return size;
 159                         }
 160                 }
 161
 162                 public T this[long index] {
 163                         get {
 164                                 return segment[index % size];
 165                         }
 166                         set {
 167                                 segment[index % size] = value;
 168                         }
 169                 }
 170
 171                 public CircularArray<T> Grow (long bottom, long top)
 172                 {
 173                         var grow = new CircularArray<T> (baseSize + 1);
 174
 175                         for (long i = top; i < bottom; i++) {
 176                                 grow.segment[i] = segment[i % size];
 177                         }
 178
 179                         return grow;
 180                 }
 181
 182                 public IEnumerable<T> GetEnumerable (long bottom, ref long top)
 183                 {
 184                         long instantTop = top;
 185                         T[] slice = new T[bottom - instantTop];
 186                         int destIndex = -1;
 187                         for (long i = instantTop; i < bottom; i++)
 188                                 slice[++destIndex] = segment[i % size];
 189
 190                         return RealGetEnumerable (slice, bottom, top, instantTop);
 191                 }
 192
 193                 IEnumerable<T> RealGetEnumerable (T[] slice, long bottom, long realTop, long initialTop)
 194                 {
 195                         int destIndex = (int)(realTop - initialTop - 1);
 196                         for (long i = realTop; i < bottom; ++i)
 197                                 yield return slice[++destIndex];
 198                 }
 199         }
 200 }
 201 #endif