mcs/class/System.Core/System.Linq.Parallel/OrderingEnumerator.cs

   1 //
   2 // OrderingEnumerator.cs
   3 //
   4 // Author:
   5 //       Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
   6 //
   7 // Copyright (c) 2010 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
  28 using System;
  29 using System.Threading;
  30 using System.Collections;
  31 using System.Collections.Generic;
  32 using System.Collections.Concurrent;
  33
  34 namespace System.Linq.Parallel
  35 {
  36         internal class OrderingEnumerator<T> : IEnumerator<T>
  37         {
  38                 internal class SlotBucket
  39                 {
  40                         readonly ConcurrentDictionary<long, T> temporaryArea = new ConcurrentDictionary<long, T> ();
  41                         readonly KeyValuePair<long, T>[] stagingArea;
  42
  43                         long currentIndex;
  44                         readonly int count;
  45
  46                         CountdownEvent stagingCount;
  47                         CountdownEvent participantCount;
  48
  49                         CancellationTokenSource src = new CancellationTokenSource ();
  50                         CancellationToken mergedToken;
  51
  52                         public SlotBucket (int count, CancellationToken token)
  53                         {
  54                                 this.count = count;
  55                                 stagingCount = new CountdownEvent (count);
  56                                 participantCount = new CountdownEvent (count);
  57                                 stagingArea = new KeyValuePair<long, T>[count];
  58                                 currentIndex = -count;
  59                                 mergedToken = CancellationTokenSource.CreateLinkedTokenSource (src.Token, token).Token;
  60                         }
  61
  62                         public void Add (KeyValuePair<long, T> value)
  63                         {
  64                                 long index = value.Key;
  65
  66                                 if (index >= currentIndex && index < currentIndex + count) {
  67                                         stagingArea[index % count] = value;
  68                                         stagingCount.Signal ();
  69                                 } else {
  70                                         temporaryArea.TryAdd (index, value.Value);
  71                                         if (index >= currentIndex && index < currentIndex + count) {
  72                                                 T dummy;
  73                                                 if (temporaryArea.TryRemove (index, out dummy)) {
  74                                                         stagingArea[index % count] = value;
  75                                                         stagingCount.Signal ();
  76                                                 }
  77                                         }
  78                                 }
  79                         }
  80
  81                         // Called by each worker's endAction
  82                         public void EndParticipation ()
  83                         {
  84                                 if (participantCount.Signal ())
  85                                         src.Cancel ();
  86                         }
  87
  88                         // Called at the end with ContinueAll
  89                         public void Stop ()
  90                         {
  91                                 src.Cancel ();
  92                         }
  93
  94                         bool Skim ()
  95                         {
  96                                 bool result = false;
  97
  98                                 for (int i = 0; i < count; i++) {
  99                                         T temp;
 100                                         int index = i + (int)currentIndex;
 101
 102                                         if (stagingArea[i].Key != -1)
 103                                                 continue;
 104
 105                                         if (!temporaryArea.TryRemove (index, out temp))
 106                                                 continue;
 107
 108                                         result = true;
 109                                         stagingArea [i] = new KeyValuePair<long, T> (index, temp);
 110                                         if (stagingCount.Signal ())
 111                                                 break;
 112                                 }
 113
 114                                 return result;
 115                         }
 116
 117                         void Clean ()
 118                         {
 119                                 for (int i = 0; i < stagingArea.Length; i++)
 120                                         stagingArea[i] = new KeyValuePair<long, T> (-1, default (T));
 121                         }
 122
 123                         public KeyValuePair<long, T>[] Wait ()
 124                         {
 125                                 Clean ();
 126                                 stagingCount.Reset ();
 127
 128                                 Interlocked.Add (ref currentIndex, count);
 129
 130                                 Skim ();
 131
 132                                 while (!stagingCount.IsSet) {
 133                                         if (!participantCount.IsSet)
 134                                                 try {
 135                                                         stagingCount.Wait (mergedToken);
 136                                                 } catch {
 137                                                         Skim ();
 138                                                 }
 139
 140
 141                                         // Ok so basically we hit the case where we return null but there is actually
 142                                         // every remaining element inside temporaryArea. Thing is that index are basically getting messed up (probably)
 143                                         // So Skim doesn't see them and inaccurately say there is nothing remaining.
 144                                         // To prove this, adding a if (temporaryArea.IsEmpty) before returning null result in infinite loop
 145                                         // plus if it was a problem with something here it would show elsewhere so the problem definitely comes from
 146                                         // SelectMany.
 147                                         if (participantCount.IsSet) {
 148                                                 if (Skim ())
 149                                                         continue;
 150                                                 // Totally finished
 151                                                 if (stagingArea.Any (s => s.Key != -1))
 152                                                         break;
 153                                                 else
 154                                                         return null;
 155                                         }
 156                                 }
 157
 158                                 return stagingArea;
 159                         }
 160                 }
 161
 162                 SlotBucket slotBucket;
 163
 164                 KeyValuePair<long, T>[] slot;
 165                 int current;
 166
 167                 internal OrderingEnumerator (int num, CancellationToken token)
 168                 {
 169                         slotBucket = new SlotBucket (num, token);
 170                 }
 171
 172                 public void Dispose ()
 173                 {
 174                         slotBucket.Stop ();
 175                 }
 176
 177                 public void Reset ()
 178                 {
 179
 180                 }
 181
 182                 public bool MoveNext ()
 183                 {
 184                         do {
 185                                 if (slot == null || ++current >= slot.Length) {
 186                                         if ((slot = slotBucket.Wait ()) == null)
 187                                                 return false;
 188                                         current = 0;
 189                                 }
 190                         } while (slot[current].Key == -1);
 191
 192                         return true;
 193                 }
 194
 195                 public T Current {
 196                         get {
 197                                 return slot[current].Value;
 198                         }
 199                 }
 200
 201                 object IEnumerator.Current {
 202                         get {
 203                                 return slot[current].Value;
 204                         }
 205                 }
 206
 207                 public void Add (KeyValuePair<long, T> value, CancellationToken token)
 208                 {
 209                         slotBucket.Add (value);
 210                 }
 211
 212                 // Called by each worker's endAction
 213                 public void EndParticipation ()
 214                 {
 215                         slotBucket.EndParticipation ();
 216                 }
 217
 218                 // Called at the end with ContinueAll
 219                 public void Stop ()
 220                 {
 221                         slotBucket.Stop ();
 222                 }
 223         }
 224 }
 225 #endif