mcs/class/corlib/System.Runtime.InteropServices/SafeHandle.cs

   1 //
   2 // System.Runtime.InteropServices.SafeHandle
   3 //
   4 // Copyright (C) 2005 Novell, Inc (http://www.novell.com)
   5 //
   6 // Permission is hereby granted, free of charge, to any person obtaining
   7 // a copy of this software and associated documentation files (the
   8 // "Software"), to deal in the Software without restriction, including
   9 // without limitation the rights to use, copy, modify, merge, publish,
  10 // distribute, sublicense, and/or sell copies of the Software, and to
  11 // permit persons to whom the Software is furnished to do so, subject to
  12 // the following conditions:
  13 //
  14 // The above copyright notice and this permission notice shall be
  15 // included in all copies or substantial portions of the Software.
  16 //
  17 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  18 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  19 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  20 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  21 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  22 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  23 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  24 //
  25 // Notes:
  26 //     This code is only API complete, but it lacks the runtime support
  27 //     for CriticalFinalizerObject and any P/Invoke wrapping that might
  28 //     happen.
  29 //
  30 //     For details, see:
  31 //     http://blogs.msdn.com/cbrumme/archive/2004/02/20/77460.aspx
  32 //
  33 //     CER-like behavior is implemented for Close and DangerousAddRef
  34 //     via the try/finally uninterruptible pattern in case of async
  35 //     exceptions like ThreadAbortException.
  36 //
  37 // On implementing SafeHandles:
  38 //     http://blogs.msdn.com/bclteam/archive/2005/03/15/396335.aspx
  39 //
  40 // Issues:
  41 //
  42 //     TODO: Although DangerousAddRef has been implemented, I need to
  43 //     find out whether the runtime performs the P/Invoke if the
  44 //     handle has been disposed already.
  45 //
  46 //
  47
  48 using System;
  49 using System.Runtime.InteropServices;
  50 using System.Runtime.ConstrainedExecution;
  51 using System.Runtime.CompilerServices;
  52 using System.Threading;
  53
  54 namespace System.Runtime.InteropServices
  55 {
  56         [StructLayout (LayoutKind.Sequential)]
  57         public abstract class SafeHandle : CriticalFinalizerObject, IDisposable {
  58                 //
  59                 // Warning: the offset of handle is mapped inside the runtime
  60                 // if you move this, you must updated the runtime definition of
  61                 // MonoSafeHandle
  62                 //
  63                 protected IntPtr handle;
  64                 int refcount;
  65                 bool owns_handle;
  66
  67 #if NET_2_1
  68                 protected SafeHandle ()
  69                 {
  70                         throw new NotImplementedException ();
  71                 }
  72 #endif
  73                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.MayFail)]
  74                 protected SafeHandle (IntPtr invalidHandleValue, bool ownsHandle)
  75                 {
  76                         handle = invalidHandleValue;
  77
  78                         if (!ownsHandle) {
  79                                 GC.SuppressFinalize (this);
  80                         } else {
  81                                 owns_handle = true;
  82                         }
  83
  84                         refcount = 1;
  85                 }
  86
  87                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  88                 public void Close ()
  89                 {
  90                         if (refcount <= 0) {
  91                                 if (refcount == 0)
  92                                         throw new ObjectDisposedException (GetType ().FullName);
  93
  94                                 return;
  95                         }
  96
  97                         int newcount = 0, current = 0;
  98                         bool registered = false;
  99                         RuntimeHelpers.PrepareConstrainedRegions ();
 100                         try {
 101                                 do {
 102                                         current = refcount;
 103                                         newcount = current-1;
 104
 105                                         // perform changes in finally to avoid async interruptions
 106                                         try {}
 107                                         finally {
 108                                                 if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
 109                                                         registered = true;
 110                                         }
 111                                 } while (!registered);
 112                         } finally {
 113                                 if (registered && newcount == 0) {
 114                                         if (owns_handle && !IsInvalid)
 115                                                 ReleaseHandle ();
 116                                         refcount = -1;
 117                                 }
 118                         }
 119                 }
 120
 121                 //
 122                 // I do not know when we could not be able to increment the
 123                 // reference count and set success to false.   It might just
 124                 // be a convention used for the following code pattern:
 125                 //
 126                 // bool release = false
 127                 // try { x.DangerousAddRef (ref release); ... }
 128                 // finally { if (release) x.DangerousRelease (); }
 129                 //
 130                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.MayFail)]
 131                 public void DangerousAddRef (ref bool success)
 132                 {
 133                         if (refcount <= 0)
 134                                 throw new ObjectDisposedException (GetType ().FullName);
 135
 136                         bool registered = false;
 137                         int newcount, current;
 138                         do {
 139                                 current = refcount;
 140                                 newcount = current + 1;
 141
 142                                 if (current <= 0){
 143                                         //
 144                                         // In MS, calling sf.Close () followed by a call
 145                                         // to P/Invoke with SafeHandles throws this, but
 146                                         // am left wondering: when would "success" be
 147                                         // set to false?
 148                                         //
 149                                         throw new ObjectDisposedException (GetType ().FullName);
 150                                 }
 151
 152                                 // perform changes in finally to avoid async interruptions
 153                                 RuntimeHelpers.PrepareConstrainedRegions ();
 154                                 try {}
 155                                 finally {
 156                                         if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
 157                                                 registered = success = true;
 158                                 }
 159                         } while (!registered);
 160                 }
 161
 162                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 163                 public IntPtr DangerousGetHandle ()
 164                 {
 165                         return handle;
 166                 }
 167
 168                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 169                 public void DangerousRelease ()
 170                 {
 171                         if (refcount <= 0)
 172                                 throw new ObjectDisposedException (GetType ().FullName);
 173
 174                         int newcount, current;
 175                         do {
 176                                 current = refcount;
 177                                 newcount = current-1;
 178                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
 179
 180                         if (newcount == 0 && owns_handle && !IsInvalid){
 181                                 ReleaseHandle ();
 182                         }
 183                 }
 184
 185                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 186                 public void Dispose ()
 187                 {
 188                         Dispose (true);
 189                         GC.SuppressFinalize (this);
 190                 }
 191
 192                 //
 193                 // See documentation, this invalidates the handle without
 194                 // closing it.
 195                 //
 196                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 197                 public void SetHandleAsInvalid ()
 198                 {
 199                         refcount = -1;
 200                 }
 201
 202                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 203                 protected virtual void Dispose (bool disposing)
 204                 {
 205                         if (disposing) {
 206                                 Close ();
 207                         } else {
 208                                 if (owns_handle && !IsInvalid){
 209                                         ReleaseHandle ();
 210                                 }
 211                         }
 212                 }
 213
 214                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 215                 protected abstract bool ReleaseHandle ();
 216
 217                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 218                 protected void SetHandle (IntPtr handle)
 219                 {
 220                         this.handle = handle;
 221                 }
 222
 223                 public bool IsClosed {
 224                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 225                         get {
 226                                 return refcount <= 0;
 227                         }
 228                 }
 229
 230                 public abstract bool IsInvalid {
 231                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 232                         get;
 233                 }
 234
 235                 ~SafeHandle ()
 236                 {
 237                         Dispose (false);
 238                 }
 239         }
 240 }