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 using System.Runtime.InteropServices;
  38 using System.Runtime.ConstrainedExecution;
  39
  40
  41 namespace System.Threading
  42 {
  43         [ComVisible (true)]
  44         public sealed class ReaderWriterLock: CriticalFinalizerObject
  45         {
  46                 private int seq_num = 1;
  47                 private int state;
  48                 private int readers;
  49                 private LockQueue writer_queue;
  50                 private Hashtable reader_locks;
  51                 private int writer_lock_owner;
  52
  53                 public ReaderWriterLock()
  54                 {
  55                         writer_queue = new LockQueue (this);
  56                         reader_locks = new Hashtable ();
  57
  58                         GC.SuppressFinalize (this);
  59                 }
  60
  61                 ~ReaderWriterLock ()
  62                 {
  63                 }
  64
  65                 public bool IsReaderLockHeld {
  66                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  67                         get {
  68                                 lock (this) return reader_locks.ContainsKey (Thread.CurrentThreadId);
  69                         }
  70                 }
  71
  72                 public bool IsWriterLockHeld {
  73                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  74                         get {
  75                                 lock (this) return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
  76                         }
  77                 }
  78
  79                 public int WriterSeqNum {
  80                         get {
  81                                 lock (this) return seq_num;
  82                         }
  83                 }
  84
  85                 public void AcquireReaderLock (int millisecondsTimeout)
  86                 {
  87                         AcquireReaderLock (millisecondsTimeout, 1);
  88                 }
  89
  90                 void AcquireReaderLock (int millisecondsTimeout, int initialLockCount)
  91                 {
  92                         lock (this) {
  93                                 if (HasWriterLock ()) {
  94                                         AcquireWriterLock (millisecondsTimeout, initialLockCount);
  95                                         return;
  96                                 }
  97
  98                                 object nlocks = reader_locks [Thread.CurrentThreadId];
  99                                 if (nlocks == null)
 100                                 {
 101                                         // Not currently holding a reader lock
 102                                         // Wait if there is a write lock
 103                                         readers++;
 104                                         try {
 105                                                 if (state < 0 || !writer_queue.IsEmpty) {
 106                                                         do {
 107                                                                 if (!Monitor.Wait (this, millisecondsTimeout))
 108                                                                         throw new ApplicationException ("Timeout expired");
 109                                                         } while (state < 0);
 110                                                 }
 111                                         }
 112                                         finally {
 113                                                 readers--;
 114                                         }
 115
 116                                         reader_locks [Thread.CurrentThreadId] = initialLockCount;
 117                                         state += initialLockCount;
 118                                 }
 119                                 else {
 120                                         reader_locks [Thread.CurrentThreadId] = ((int)nlocks) + 1;
 121                                         state++;
 122                                 }
 123                         }
 124                 }
 125
 126                 public void AcquireReaderLock(TimeSpan timeout)
 127                 {
 128                         int ms = CheckTimeout (timeout);
 129                         AcquireReaderLock (ms, 1);
 130                 }
 131
 132                 public void AcquireWriterLock (int millisecondsTimeout)
 133                 {
 134                         AcquireWriterLock (millisecondsTimeout, 1);
 135                 }
 136
 137                 void AcquireWriterLock (int millisecondsTimeout, int initialLockCount)
 138                 {
 139                         lock (this) {
 140                                 if (HasWriterLock ()) {
 141                                         state--;
 142                                         return;
 143                                 }
 144
 145                                 // wait while there are reader locks or another writer lock, or
 146                                 // other threads waiting for the writer lock
 147                                 if (state != 0 || !writer_queue.IsEmpty) {
 148                                         do {
 149                                                 if (!writer_queue.Wait (millisecondsTimeout))
 150                                                         throw new ApplicationException ("Timeout expired");
 151                                         } while (state != 0);
 152                                 }
 153
 154                                 state = -initialLockCount;
 155                                 writer_lock_owner = Thread.CurrentThreadId;
 156                                 seq_num++;
 157                         }
 158                 }
 159
 160                 public void AcquireWriterLock(TimeSpan timeout) {
 161                         int ms = CheckTimeout (timeout);
 162                         AcquireWriterLock (ms, 1);
 163                 }
 164
 165                 public bool AnyWritersSince(int seqNum) {
 166                         lock (this) {
 167                                 return (this.seq_num > seqNum);
 168                         }
 169                 }
 170
 171                 public void DowngradeFromWriterLock(ref LockCookie lockCookie)
 172                 {
 173                         lock (this) {
 174                                 if (!HasWriterLock())
 175                                         throw new ApplicationException ("The thread does not have the writer lock.");
 176
 177                                 state = lockCookie.ReaderLocks;
 178                                 reader_locks [Thread.CurrentThreadId] = state;
 179                                 if (readers > 0) {
 180                                         Monitor.PulseAll (this);
 181                                 }
 182
 183                                 // MSDN: A thread does not block when downgrading from the writer lock,
 184                                 // even if other threads are waiting for the writer lock
 185                         }
 186                 }
 187
 188                 public LockCookie ReleaseLock()
 189                 {
 190                         LockCookie cookie;
 191                         lock (this) {
 192                                 cookie = GetLockCookie ();
 193                                 if (cookie.WriterLocks != 0)
 194                                         ReleaseWriterLock (cookie.WriterLocks);
 195                                 else if (cookie.ReaderLocks != 0) {
 196                                         ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
 197                                 }
 198                         }
 199                         return cookie;
 200                 }
 201
 202                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 203                 public void ReleaseReaderLock()
 204                 {
 205                         lock (this) {
 206                                 if (HasWriterLock ()) {
 207                                         ReleaseWriterLock ();
 208                                         return;
 209                                 }
 210                                 else if (state > 0) {
 211                                         object read_lock_count = reader_locks [Thread.CurrentThreadId];
 212                                         if (read_lock_count != null) {
 213                                                 ReleaseReaderLock ((int)read_lock_count, 1);
 214                                                 return;
 215                                         }
 216                                 }
 217
 218                                 throw new ApplicationException ("The thread does not have any reader or writer locks.");
 219                         }
 220                 }
 221
 222                 void ReleaseReaderLock (int currentCount, int releaseCount)
 223                 {
 224                         int new_count = currentCount - releaseCount;
 225
 226                         if (new_count == 0)
 227                                 reader_locks.Remove (Thread.CurrentThreadId);
 228                         else
 229                                 reader_locks [Thread.CurrentThreadId] = new_count;
 230
 231                         state -= releaseCount;
 232                         if (state == 0 && !writer_queue.IsEmpty)
 233                                 writer_queue.Pulse ();
 234                 }
 235
 236                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 237                 public void ReleaseWriterLock()
 238                 {
 239                         lock (this) {
 240                                 if (!HasWriterLock())
 241                                         throw new ApplicationException ("The thread does not have the writer lock.");
 242
 243                                 ReleaseWriterLock (1);
 244                         }
 245                 }
 246
 247                 void ReleaseWriterLock (int releaseCount)
 248                 {
 249                         state += releaseCount;
 250                         if (state == 0) {
 251                                 if (readers > 0) {
 252                                         Monitor.PulseAll (this);
 253                                 }
 254                                 else if (!writer_queue.IsEmpty)
 255                                         writer_queue.Pulse ();
 256                         }
 257                 }
 258
 259                 public void RestoreLock(ref LockCookie lockCookie)
 260                 {
 261                         lock (this) {
 262                                 if (lockCookie.WriterLocks != 0)
 263                                         AcquireWriterLock (-1, lockCookie.WriterLocks);
 264                                 else if (lockCookie.ReaderLocks != 0)
 265                                         AcquireReaderLock (-1, lockCookie.ReaderLocks);
 266                         }
 267                 }
 268
 269                 public LockCookie UpgradeToWriterLock(int millisecondsTimeout)
 270                 {
 271                         LockCookie cookie;
 272                         lock (this) {
 273                                 cookie = GetLockCookie ();
 274                                 if (cookie.WriterLocks != 0) {
 275                                         state--;
 276                                         return cookie;
 277                                 }
 278
 279                                 if (cookie.ReaderLocks != 0)
 280                                         ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
 281                         }
 282
 283                         // Don't do this inside the lock, since it can cause a deadlock.
 284                         AcquireWriterLock (millisecondsTimeout);
 285                         return cookie;
 286                 }
 287
 288                 public LockCookie UpgradeToWriterLock(TimeSpan timeout)
 289                 {
 290                         int ms = CheckTimeout (timeout);
 291                         return UpgradeToWriterLock (ms);
 292                 }
 293
 294                 LockCookie GetLockCookie ()
 295                 {
 296                         LockCookie cookie = new LockCookie (Thread.CurrentThreadId);
 297
 298                         if (HasWriterLock())
 299                                 cookie.WriterLocks = -state;
 300                         else {
 301                                 object locks = reader_locks [Thread.CurrentThreadId];
 302                                 if (locks != null) cookie.ReaderLocks = (int)locks;
 303                         }
 304                         return cookie;
 305                 }
 306
 307                 bool HasWriterLock ()
 308                 {
 309                         return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
 310                 }
 311
 312                 private int CheckTimeout (TimeSpan timeout)
 313                 {
 314                         int ms = (int) timeout.TotalMilliseconds;
 315
 316                         if (ms < -1)
 317                                 throw new ArgumentOutOfRangeException ("timeout",
 318                                                 "Number must be either non-negative or -1");
 319                         return ms;
 320                 }
 321         }
 322 }
 323