mcs/class/corlib/System.Threading/ReaderWriterLock.cs

   1 //
   2 // System.Threading.ReaderWriterLock.cs
   3 //
   4 // Author:
   5 //   Dick Porter (dick@ximian.com)
   6 //   Jackson Harper (jackson@ximian.com)
   7 //   Lluis Sanchez Gual (lluis@ximian.com)
   8 //
   9 // (C) Ximian, Inc.  http://www.ximian.com
  10 // (C) 2004 Novell, Inc (http://www.novell.com)
  11 //
  12
  13 //
  14 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
  15 //
  16 // Permission is hereby granted, free of charge, to any person obtaining
  17 // a copy of this software and associated documentation files (the
  18 // "Software"), to deal in the Software without restriction, including
  19 // without limitation the rights to use, copy, modify, merge, publish,
  20 // distribute, sublicense, and/or sell copies of the Software, and to
  21 // permit persons to whom the Software is furnished to do so, subject to
  22 // the following conditions:
  23 //
  24 // The above copyright notice and this permission notice shall be
  25 // included in all copies or substantial portions of the Software.
  26 //
  27 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  28 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  29 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  30 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  31 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  32 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  33 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  34 //
  35
  36 using System.Collections;
  37
  38 #if NET_2_0
  39 using System.Runtime.InteropServices;
  40 using System.Runtime.ConstrainedExecution;
  41 #endif
  42
  43 namespace System.Threading
  44 {
  45 #if NET_2_0
  46         [ComVisible (true)]
  47         public sealed class ReaderWriterLock: CriticalFinalizerObject
  48 #else
  49         public sealed class ReaderWriterLock
  50 #endif
  51         {
  52                 private int seq_num = 1;
  53                 private int state;
  54                 private int readers;
  55                 private LockQueue writer_queue;
  56                 private Hashtable reader_locks;
  57                 private int writer_lock_owner;
  58
  59                 public ReaderWriterLock()
  60                 {
  61                         writer_queue = new LockQueue (this);
  62                         reader_locks = new Hashtable ();
  63
  64 #if NET_2_0
  65                         GC.SuppressFinalize (this);
  66 #endif
  67                 }
  68
  69 #if NET_2_0
  70                 [MonoTODO]
  71                 ~ReaderWriterLock ()
  72                 {
  73                 }
  74 #endif
  75
  76                 public bool IsReaderLockHeld {
  77 #if NET_2_0
  78                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  79 #endif
  80                         get {
  81                                 lock (this) return reader_locks.ContainsKey (Thread.CurrentThreadId);
  82                         }
  83                 }
  84
  85                 public bool IsWriterLockHeld {
  86 #if NET_2_0
  87                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  88 #endif
  89                         get {
  90                                 lock (this) return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
  91                         }
  92                 }
  93
  94                 public int WriterSeqNum {
  95                         get {
  96                                 lock (this) return seq_num;
  97                         }
  98                 }
  99
 100                 public void AcquireReaderLock (int millisecondsTimeout)
 101                 {
 102                         AcquireReaderLock (millisecondsTimeout, 1);
 103                 }
 104
 105                 void AcquireReaderLock (int millisecondsTimeout, int initialLockCount)
 106                 {
 107                         lock (this) {
 108                                 if (HasWriterLock ()) {
 109                                         AcquireWriterLock (millisecondsTimeout, initialLockCount);
 110                                         return;
 111                                 }
 112
 113                                 object nlocks = reader_locks [Thread.CurrentThreadId];
 114                                 if (nlocks == null)
 115                                 {
 116                                         // Not currently holding a reader lock
 117                                         // Wait if there is a write lock
 118                                         readers++;
 119                                         try {
 120                                                 if (state < 0 || !writer_queue.IsEmpty) {
 121                                                         do {
 122                                                                 if (!Monitor.Wait (this, millisecondsTimeout))
 123                                                                         throw new ApplicationException ("Timeout expired");
 124                                                         } while (state < 0);
 125                                                 }
 126                                         }
 127                                         finally {
 128                                                 readers--;
 129                                         }
 130
 131                                         reader_locks [Thread.CurrentThreadId] = initialLockCount;
 132                                         state += initialLockCount;
 133                                 }
 134                                 else {
 135                                         reader_locks [Thread.CurrentThreadId] = ((int)nlocks) + 1;
 136                                         state++;
 137                                 }
 138                         }
 139                 }
 140
 141                 public void AcquireReaderLock(TimeSpan timeout)
 142                 {
 143                         int ms = CheckTimeout (timeout);
 144                         AcquireReaderLock (ms, 1);
 145                 }
 146
 147                 public void AcquireWriterLock (int millisecondsTimeout)
 148                 {
 149                         AcquireWriterLock (millisecondsTimeout, 1);
 150                 }
 151
 152                 void AcquireWriterLock (int millisecondsTimeout, int initialLockCount)
 153                 {
 154                         lock (this) {
 155                                 if (HasWriterLock ()) {
 156                                         state--;
 157                                         return;
 158                                 }
 159
 160                                 // wait while there are reader locks or another writer lock, or
 161                                 // other threads waiting for the writer lock
 162                                 if (state != 0 || !writer_queue.IsEmpty) {
 163                                         do {
 164                                                 if (!writer_queue.Wait (millisecondsTimeout))
 165                                                         throw new ApplicationException ("Timeout expired");
 166                                         } while (state != 0);
 167                                 }
 168
 169                                 state = -initialLockCount;
 170                                 writer_lock_owner = Thread.CurrentThreadId;
 171                                 seq_num++;
 172                         }
 173                 }
 174
 175                 public void AcquireWriterLock(TimeSpan timeout) {
 176                         int ms = CheckTimeout (timeout);
 177                         AcquireWriterLock (ms, 1);
 178                 }
 179
 180                 public bool AnyWritersSince(int seqNum) {
 181                         lock (this) {
 182                                 return (this.seq_num > seqNum);
 183                         }
 184                 }
 185
 186                 public void DowngradeFromWriterLock(ref LockCookie lockCookie)
 187                 {
 188                         lock (this) {
 189                                 if (!HasWriterLock())
 190                                         throw new ApplicationException ("The thread does not have the writer lock.");
 191
 192                                 state = lockCookie.ReaderLocks;
 193                                 reader_locks [Thread.CurrentThreadId] = state;
 194                                 if (readers > 0) {
 195                                         Monitor.PulseAll (this);
 196                                 }
 197
 198                                 // MSDN: A thread does not block when downgrading from the writer lock,
 199                                 // even if other threads are waiting for the writer lock
 200                         }
 201                 }
 202
 203                 public LockCookie ReleaseLock()
 204                 {
 205                         LockCookie cookie;
 206                         lock (this) {
 207                                 cookie = GetLockCookie ();
 208                                 if (cookie.WriterLocks != 0)
 209                                         ReleaseWriterLock (cookie.WriterLocks);
 210                                 else if (cookie.ReaderLocks != 0) {
 211                                         ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
 212                                 }
 213                         }
 214                         return cookie;
 215                 }
 216
 217 #if NET_2_0
 218                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 219 #endif
 220                 public void ReleaseReaderLock()
 221                 {
 222                         lock (this) {
 223                                 if (HasWriterLock ()) {
 224                                         ReleaseWriterLock ();
 225                                         return;
 226                                 }
 227                                 else if (state > 0) {
 228                                         object read_lock_count = reader_locks [Thread.CurrentThreadId];
 229                                         if (read_lock_count != null) {
 230                                                 ReleaseReaderLock ((int)read_lock_count, 1);
 231                                                 return;
 232                                         }
 233                                 }
 234
 235                                 throw new ApplicationException ("The thread does not have any reader or writer locks.");
 236                         }
 237                 }
 238
 239                 void ReleaseReaderLock (int currentCount, int releaseCount)
 240                 {
 241                         int new_count = currentCount - releaseCount;
 242
 243                         if (new_count == 0)
 244                                 reader_locks.Remove (Thread.CurrentThreadId);
 245                         else
 246                                 reader_locks [Thread.CurrentThreadId] = new_count;
 247
 248                         state -= releaseCount;
 249                         if (state == 0 && !writer_queue.IsEmpty)
 250                                 writer_queue.Pulse ();
 251                 }
 252
 253 #if NET_2_0
 254                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 255 #endif
 256                 public void ReleaseWriterLock()
 257                 {
 258                         lock (this) {
 259                                 if (!HasWriterLock())
 260                                         throw new ApplicationException ("The thread does not have the writer lock.");
 261
 262                                 ReleaseWriterLock (1);
 263                         }
 264                 }
 265
 266                 void ReleaseWriterLock (int releaseCount)
 267                 {
 268                         state += releaseCount;
 269                         if (state == 0) {
 270                                 if (readers > 0) {
 271                                         Monitor.PulseAll (this);
 272                                 }
 273                                 else if (!writer_queue.IsEmpty)
 274                                         writer_queue.Pulse ();
 275                         }
 276                 }
 277
 278                 public void RestoreLock(ref LockCookie lockCookie)
 279                 {
 280                         lock (this) {
 281                                 if (lockCookie.WriterLocks != 0)
 282                                         AcquireWriterLock (-1, lockCookie.WriterLocks);
 283                                 else if (lockCookie.ReaderLocks != 0)
 284                                         AcquireReaderLock (-1, lockCookie.ReaderLocks);
 285                         }
 286                 }
 287
 288                 public LockCookie UpgradeToWriterLock(int millisecondsTimeout)
 289                 {
 290                         LockCookie cookie;
 291                         lock (this) {
 292                                 cookie = GetLockCookie ();
 293                                 if (cookie.WriterLocks != 0) {
 294                                         state--;
 295                                         return cookie;
 296                                 }
 297
 298                                 if (cookie.ReaderLocks != 0)
 299                                         ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
 300                         }
 301
 302                         // Don't do this inside the lock, since it can cause a deadlock.
 303                         AcquireWriterLock (millisecondsTimeout);
 304                         return cookie;
 305                 }
 306
 307                 public LockCookie UpgradeToWriterLock(TimeSpan timeout)
 308                 {
 309                         int ms = CheckTimeout (timeout);
 310                         return UpgradeToWriterLock (ms);
 311                 }
 312
 313                 LockCookie GetLockCookie ()
 314                 {
 315                         LockCookie cookie = new LockCookie (Thread.CurrentThreadId);
 316
 317                         if (HasWriterLock())
 318                                 cookie.WriterLocks = -state;
 319                         else {
 320                                 object locks = reader_locks [Thread.CurrentThreadId];
 321                                 if (locks != null) cookie.ReaderLocks = (int)locks;
 322                         }
 323                         return cookie;
 324                 }
 325
 326                 bool HasWriterLock ()
 327                 {
 328                         return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
 329                 }
 330
 331                 private int CheckTimeout (TimeSpan timeout)
 332                 {
 333                         int ms = (int) timeout.TotalMilliseconds;
 334
 335                         if (ms < -1)
 336                                 throw new ArgumentOutOfRangeException ("timeout",
 337                                                 "Number must be either non-negative or -1");
 338                         return ms;
 339                 }
 340         }
 341 }
 342