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
  65                 public bool IsReaderLockHeld {
  66 #if NET_2_0
  67                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  68 #endif
  69                         get {
  70                                 lock (this) return reader_locks.ContainsKey (Thread.CurrentThreadId);
  71                         }
  72                 }
  73
  74                 public bool IsWriterLockHeld {
  75 #if NET_2_0
  76                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  77 #endif
  78                         get {
  79                                 lock (this) return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
  80                         }
  81                 }
  82
  83                 public int WriterSeqNum {
  84                         get {
  85                                 lock (this) return seq_num;
  86                         }
  87                 }
  88
  89                 public void AcquireReaderLock (int millisecondsTimeout)
  90                 {
  91                         AcquireReaderLock (millisecondsTimeout, 1);
  92                 }
  93
  94                 void AcquireReaderLock (int millisecondsTimeout, int initialLockCount)
  95                 {
  96                         lock (this) {
  97                                 if (HasWriterLock ()) {
  98                                         AcquireWriterLock (millisecondsTimeout, initialLockCount);
  99                                         return;
 100                                 }
 101
 102                                 object nlocks = reader_locks [Thread.CurrentThreadId];
 103                                 if (nlocks == null)
 104                                 {
 105                                         // Not currently holding a reader lock
 106                                         // Wait if there is a write lock
 107                                         readers++;
 108                                         try {
 109                                                 if (state < 0 || !writer_queue.IsEmpty) {
 110                                                         do {
 111                                                                 if (!Monitor.Wait (this, millisecondsTimeout))
 112                                                                         throw new ApplicationException ("Timeout expired");
 113                                                         } while (state < 0);
 114                                                 }
 115                                         }
 116                                         finally {
 117                                                 readers--;
 118                                         }
 119
 120                                         reader_locks [Thread.CurrentThreadId] = initialLockCount;
 121                                         state += initialLockCount;
 122                                 }
 123                                 else {
 124                                         reader_locks [Thread.CurrentThreadId] = ((int)nlocks) + 1;
 125                                         state++;
 126                                 }
 127                         }
 128                 }
 129
 130                 public void AcquireReaderLock(TimeSpan timeout)
 131                 {
 132                         int ms = CheckTimeout (timeout);
 133                         AcquireReaderLock (ms, 1);
 134                 }
 135
 136                 public void AcquireWriterLock (int millisecondsTimeout)
 137                 {
 138                         AcquireWriterLock (millisecondsTimeout, 1);
 139                 }
 140
 141                 void AcquireWriterLock (int millisecondsTimeout, int initialLockCount)
 142                 {
 143                         lock (this) {
 144                                 if (HasWriterLock ()) {
 145                                         state--;
 146                                         return;
 147                                 }
 148
 149                                 // wait while there are reader locks or another writer lock, or
 150                                 // other threads waiting for the writer lock
 151                                 if (state != 0 || !writer_queue.IsEmpty) {
 152                                         do {
 153                                                 if (!writer_queue.Wait (millisecondsTimeout))
 154                                                         throw new ApplicationException ("Timeout expired");
 155                                         } while (state != 0);
 156                                 }
 157
 158                                 state = -initialLockCount;
 159                                 writer_lock_owner = Thread.CurrentThreadId;
 160                                 seq_num++;
 161                         }
 162                 }
 163
 164                 public void AcquireWriterLock(TimeSpan timeout) {
 165                         int ms = CheckTimeout (timeout);
 166                         AcquireWriterLock (ms, 1);
 167                 }
 168
 169                 public bool AnyWritersSince(int seqNum) {
 170                         lock (this) {
 171                                 return (this.seq_num > seqNum);
 172                         }
 173                 }
 174
 175                 public void DowngradeFromWriterLock(ref LockCookie lockCookie)
 176                 {
 177                         lock (this) {
 178                                 if (!HasWriterLock())
 179                                         throw new ApplicationException ("The thread does not have the writer lock.");
 180
 181                                 state = lockCookie.ReaderLocks;
 182                                 reader_locks [Thread.CurrentThreadId] = state;
 183                                 if (readers > 0) {
 184                                         Monitor.PulseAll (this);
 185                                 }
 186
 187                                 // MSDN: A thread does not block when downgrading from the writer lock,
 188                                 // even if other threads are waiting for the writer lock
 189                         }
 190                 }
 191
 192                 public LockCookie ReleaseLock()
 193                 {
 194                         LockCookie cookie;
 195                         lock (this) {
 196                                 cookie = GetLockCookie ();
 197                                 if (cookie.WriterLocks != 0)
 198                                         ReleaseWriterLock (cookie.WriterLocks);
 199                                 else if (cookie.ReaderLocks != 0) {
 200                                         ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
 201                                 }
 202                         }
 203                         return cookie;
 204                 }
 205
 206 #if NET_2_0
 207                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 208 #endif
 209                 public void ReleaseReaderLock()
 210                 {
 211                         lock (this) {
 212                                 if (HasWriterLock ()) {
 213                                         ReleaseWriterLock ();
 214                                         return;
 215                                 }
 216                                 else if (state > 0) {
 217                                         object read_lock_count = reader_locks [Thread.CurrentThreadId];
 218                                         if (read_lock_count != null) {
 219                                                 ReleaseReaderLock ((int)read_lock_count, 1);
 220                                                 return;
 221                                         }
 222                                 }
 223
 224                                 throw new ApplicationException ("The thread does not have any reader or writer locks.");
 225                         }
 226                 }
 227
 228                 void ReleaseReaderLock (int currentCount, int releaseCount)
 229                 {
 230                         int new_count = currentCount - releaseCount;
 231
 232                         if (new_count == 0)
 233                                 reader_locks.Remove (Thread.CurrentThreadId);
 234                         else
 235                                 reader_locks [Thread.CurrentThreadId] = new_count;
 236
 237                         state -= releaseCount;
 238                         if (state == 0 && !writer_queue.IsEmpty)
 239                                 writer_queue.Pulse ();
 240                 }
 241
 242 #if NET_2_0
 243                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 244 #endif
 245                 public void ReleaseWriterLock()
 246                 {
 247                         lock (this) {
 248                                 if (!HasWriterLock())
 249                                         throw new ApplicationException ("The thread does not have the writer lock.");
 250
 251                                 ReleaseWriterLock (1);
 252                         }
 253                 }
 254
 255                 void ReleaseWriterLock (int releaseCount)
 256                 {
 257                         state += releaseCount;
 258                         if (state == 0) {
 259                                 if (readers > 0) {
 260                                         Monitor.PulseAll (this);
 261                                 }
 262                                 else if (!writer_queue.IsEmpty)
 263                                         writer_queue.Pulse ();
 264                         }
 265                 }
 266
 267                 public void RestoreLock(ref LockCookie lockCookie)
 268                 {
 269                         lock (this) {
 270                                 if (lockCookie.WriterLocks != 0)
 271                                         AcquireWriterLock (-1, lockCookie.WriterLocks);
 272                                 else if (lockCookie.ReaderLocks != 0)
 273                                         AcquireReaderLock (-1, lockCookie.ReaderLocks);
 274                         }
 275                 }
 276
 277                 public LockCookie UpgradeToWriterLock(int millisecondsTimeout)
 278                 {
 279                         LockCookie cookie;
 280                         lock (this) {
 281                                 cookie = GetLockCookie ();
 282                                 if (cookie.WriterLocks != 0) {
 283                                         state--;
 284                                         return cookie;
 285                                 }
 286
 287                                 if (cookie.ReaderLocks != 0)
 288                                         ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
 289                         }
 290
 291                         // Don't do this inside the lock, since it can cause a deadlock.
 292                         AcquireWriterLock (millisecondsTimeout);
 293                         return cookie;
 294                 }
 295
 296                 public LockCookie UpgradeToWriterLock(TimeSpan timeout)
 297                 {
 298                         int ms = CheckTimeout (timeout);
 299                         return UpgradeToWriterLock (ms);
 300                 }
 301
 302                 LockCookie GetLockCookie ()
 303                 {
 304                         LockCookie cookie = new LockCookie (Thread.CurrentThreadId);
 305
 306                         if (HasWriterLock())
 307                                 cookie.WriterLocks = -state;
 308                         else {
 309                                 object locks = reader_locks [Thread.CurrentThreadId];
 310                                 if (locks != null) cookie.ReaderLocks = (int)locks;
 311                         }
 312                         return cookie;
 313                 }
 314
 315                 bool HasWriterLock ()
 316                 {
 317                         return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
 318                 }
 319
 320                 private int CheckTimeout (TimeSpan timeout)
 321                 {
 322                         int ms = (int) timeout.TotalMilliseconds;
 323
 324                         if (ms < -1)
 325                                 throw new ArgumentOutOfRangeException ("timeout",
 326                                                 "Number must be either non-negative or -1");
 327                         return ms;
 328                 }
 329         }
 330 }
 331