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         class CyclicDeque<T> : IConcurrentDeque<T>
  43         {
  44                 const int BaseSize = 11;
  45
  46                 long bottom;
  47                 long top;
  48                 long upperBound;
  49                 CircularArray<T> array = new CircularArray<T> (BaseSize);
  50
  51                 public void PushBottom (T obj)
  52                 {
  53                         /* Read is implemented as a simple load operation on 64bits
  54                          * so no need to make the distinction ourselves
  55                          */
  56                         long b = Interlocked.Read (ref bottom);
  57                         var a = array;
  58
  59                         // Take care of growing
  60                         if (b - upperBound >= a.Size - 1) {
  61                                 upperBound = Interlocked.Read (ref top);
  62                                 a = a.Grow (b, upperBound);
  63                                 array = a;
  64                         }
  65
  66                         // Register the new value
  67                         a.segment[b % a.size] = obj;
  68                         Interlocked.Increment (ref bottom);
  69                 }
  70
  71                 public PopResult PopBottom (out T obj)
  72                 {
  73                         obj = default (T);
  74
  75                         long b = Interlocked.Decrement (ref bottom);
  76                         var a = array;
  77                         long t = Interlocked.Read (ref top);
  78                         long size = b - t;
  79
  80                         if (size < 0) {
  81                                 // Set bottom to t
  82                                 Interlocked.Add (ref bottom, t - b);
  83                                 return PopResult.Empty;
  84                         }
  85
  86                         obj = a.segment[b % a.size];
  87                         if (size > 0)
  88                                 return PopResult.Succeed;
  89                         Interlocked.Add (ref bottom, t + 1 - b);
  90
  91                         if (Interlocked.CompareExchange (ref top, t + 1, t) != t)
  92                                 return PopResult.Empty;
  93
  94                         return PopResult.Succeed;
  95                 }
  96
  97                 public PopResult PopTop (out T obj)
  98                 {
  99                         obj = default (T);
 100
 101                         long t = Interlocked.Read (ref top);
 102                         long b = Interlocked.Read (ref bottom);
 103
 104                         if (b - t <= 0)
 105                                 return PopResult.Empty;
 106
 107                         if (Interlocked.CompareExchange (ref top, t + 1, t) != t)
 108                                 return PopResult.Abort;
 109
 110                         var a = array;
 111                         obj = a.segment[t % a.size];
 112
 113                         return PopResult.Succeed;
 114                 }
 115
 116                 public IEnumerable<T> GetEnumerable ()
 117                 {
 118                         var a = array;
 119                         return a.GetEnumerable (bottom, ref top);
 120                 }
 121         }
 122
 123         internal class CircularArray<T>
 124         {
 125                 readonly int baseSize;
 126                 public readonly int size;
 127                 public readonly T[] segment;
 128
 129                 public CircularArray (int baseSize)
 130                 {
 131                         this.baseSize = baseSize;
 132                         this.size = 1 << baseSize;
 133                         this.segment = new T[size];
 134                 }
 135
 136                 public long Size {
 137                         get {
 138                                 return size;
 139                         }
 140                 }
 141
 142                 public T this[long index] {
 143                         get {
 144                                 return segment[index % size];
 145                         }
 146                         set {
 147                                 segment[index % size] = value;
 148                         }
 149                 }
 150
 151                 public CircularArray<T> Grow (long bottom, long top)
 152                 {
 153                         var grow = new CircularArray<T> (baseSize + 1);
 154
 155                         for (long i = top; i < bottom; i++) {
 156                                 grow.segment[i] = segment[i % size];
 157                         }
 158
 159                         return grow;
 160                 }
 161
 162                 public IEnumerable<T> GetEnumerable (long bottom, ref long top)
 163                 {
 164                         long instantTop = top;
 165                         T[] slice = new T[bottom - instantTop];
 166                         int destIndex = -1;
 167                         for (long i = instantTop; i < bottom; i++)
 168                                 slice[++destIndex] = segment[i % size];
 169
 170                         return RealGetEnumerable (slice, bottom, top, instantTop);
 171                 }
 172
 173                 IEnumerable<T> RealGetEnumerable (T[] slice, long bottom, long realTop, long initialTop)
 174                 {
 175                         int destIndex = (int)(realTop - initialTop - 1);
 176                         for (long i = realTop; i < bottom; ++i)
 177                                 yield return slice[++destIndex];
 178                 }
 179         }
 180 }
 181 #endif