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