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                 IntPtr invalid_handle_value;
  65                 int refcount;
  66                 bool owns_handle;
  67
  68 #if NET_2_1
  69                 protected SafeHandle ()
  70                 {
  71                         throw new NotImplementedException ();
  72                 }
  73 #endif
  74                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.MayFail)]
  75                 protected SafeHandle (IntPtr invalidHandleValue, bool ownsHandle)
  76                 {
  77                         invalid_handle_value = invalidHandleValue;
  78
  79                         if (!ownsHandle) {
  80                                 GC.SuppressFinalize (this);
  81                         } else {
  82                                 owns_handle = true;
  83                         }
  84
  85                         refcount = 1;
  86                 }
  87
  88                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  89                 public void Close ()
  90                 {
  91                         if (refcount == 0)
  92                                 throw new ObjectDisposedException (GetType ().FullName);
  93
  94                         int newcount = 0, current = 0;
  95                         bool registered = false;
  96                         RuntimeHelpers.PrepareConstrainedRegions ();
  97                         try {
  98                                 do {
  99                                         current = refcount;
 100                                         newcount = current-1;
 101
 102                                         // perform changes in finally to avoid async interruptions
 103                                         try {}
 104                                         finally {
 105                                                 if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
 106                                                         registered = true;
 107                                         }
 108                                 } while (!registered);
 109                         } finally {
 110                                 if (registered && newcount == 0 && owns_handle && !IsInvalid){
 111                                         ReleaseHandle ();
 112                                         handle = invalid_handle_value;
 113                                         refcount = -1;
 114                                 }
 115                         }
 116                 }
 117
 118                 //
 119                 // I do not know when we could not be able to increment the
 120                 // reference count and set success to false.   It might just
 121                 // be a convention used for the following code pattern:
 122                 //
 123                 // bool release = false
 124                 // try { x.DangerousAddRef (ref release); ... }
 125                 // finally { if (release) x.DangerousRelease (); }
 126                 //
 127                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.MayFail)]
 128                 public void DangerousAddRef (ref bool success)
 129                 {
 130                         if (refcount <= 0)
 131                                 throw new ObjectDisposedException (GetType ().FullName);
 132
 133                         bool registered = false;
 134                         int newcount, current;
 135                         do {
 136                                 current = refcount;
 137                                 newcount = current + 1;
 138
 139                                 if (current <= 0){
 140                                         //
 141                                         // In MS, calling sf.Close () followed by a call
 142                                         // to P/Invoke with SafeHandles throws this, but
 143                                         // am left wondering: when would "success" be
 144                                         // set to false?
 145                                         //
 146                                         throw new ObjectDisposedException (GetType ().FullName);
 147                                 }
 148
 149                                 // perform changes in finally to avoid async interruptions
 150                                 RuntimeHelpers.PrepareConstrainedRegions ();
 151                                 try {}
 152                                 finally {
 153                                         if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
 154                                                 registered = success = true;
 155                                 }
 156                         } while (!registered);
 157                 }
 158
 159                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 160                 public IntPtr DangerousGetHandle ()
 161                 {
 162                         if (refcount <= 0){
 163                                 throw new ObjectDisposedException (GetType ().FullName);
 164                         }
 165
 166                         return handle;
 167                 }
 168
 169                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 170                 public void DangerousRelease ()
 171                 {
 172                         if (refcount <= 0)
 173                                 throw new ObjectDisposedException (GetType ().FullName);
 174
 175                         int newcount, current;
 176                         do {
 177                                 current = refcount;
 178                                 newcount = current-1;
 179                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
 180
 181                         if (newcount == 0 && owns_handle && !IsInvalid){
 182                                 ReleaseHandle ();
 183                                 handle = invalid_handle_value;
 184                         }
 185                 }
 186
 187                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 188                 public void Dispose ()
 189                 {
 190                         Dispose (true);
 191                         GC.SuppressFinalize (this);
 192                 }
 193
 194                 //
 195                 // See documentation, this invalidates the handle without
 196                 // closing it.
 197                 //
 198                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 199                 public void SetHandleAsInvalid ()
 200                 {
 201                         handle = invalid_handle_value;
 202                 }
 203
 204                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 205                 protected virtual void Dispose (bool disposing)
 206                 {
 207                         if (disposing) {
 208                                 Close ();
 209                         } else {
 210                                 if (owns_handle && !IsInvalid){
 211                                         ReleaseHandle ();
 212                                         handle = invalid_handle_value;
 213                                 }
 214                         }
 215                 }
 216
 217                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 218                 protected abstract bool ReleaseHandle ();
 219
 220                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 221                 protected void SetHandle (IntPtr handle)
 222                 {
 223                         this.handle = handle;
 224                 }
 225
 226                 public bool IsClosed {
 227                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 228                         get {
 229                                 return refcount <= 0;
 230                         }
 231                 }
 232
 233                 public abstract bool IsInvalid {
 234                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 235                         get;
 236                 }
 237
 238                 ~SafeHandle ()
 239                 {
 240                         Dispose (false);
 241                 }
 242         }
 243 }