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 = 0;
  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                         owns_handle = ownsHandle;
  79                         refcount = 1;
  80                 }
  81
  82                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  83                 public void Close ()
  84                 {
  85                         if (refcount == 0)
  86                                 throw new ObjectDisposedException (GetType ().FullName);
  87
  88                         int newcount = 0, current = 0;
  89                         bool registered = false;
  90                         RuntimeHelpers.PrepareConstrainedRegions ();
  91                         try {
  92                                 do {
  93                                         current = refcount;
  94                                         newcount = current-1;
  95
  96                                         // perform changes in finally to avoid async interruptions
  97                                         try {}
  98                                         finally {
  99                                                 if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
 100                                                         registered = true;
 101                                         }
 102                                 } while (!registered);
 103                         } finally {
 104                                 if (registered && newcount == 0 && owns_handle && !IsInvalid){
 105                                         ReleaseHandle ();
 106                                         handle = invalid_handle_value;
 107                                         refcount = -1;
 108                                 }
 109                         }
 110                 }
 111
 112                 //
 113                 // I do not know when we could not be able to increment the
 114                 // reference count and set success to false.   It might just
 115                 // be a convention used for the following code pattern:
 116                 //
 117                 // bool release = false
 118                 // try { x.DangerousAddRef (ref release); ... }
 119                 // finally { if (release) x.DangerousRelease (); }
 120                 //
 121                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.MayFail)]
 122                 public void DangerousAddRef (ref bool success)
 123                 {
 124                         if (refcount <= 0)
 125                                 throw new ObjectDisposedException (GetType ().FullName);
 126
 127                         bool registered = false;
 128                         int newcount, current;
 129                         do {
 130                                 current = refcount;
 131                                 newcount = current + 1;
 132
 133                                 if (current <= 0){
 134                                         //
 135                                         // In MS, calling sf.Close () followed by a call
 136                                         // to P/Invoke with SafeHandles throws this, but
 137                                         // am left wondering: when would "success" be
 138                                         // set to false?
 139                                         //
 140                                         throw new ObjectDisposedException (GetType ().FullName);
 141                                 }
 142
 143                                 // perform changes in finally to avoid async interruptions
 144                                 RuntimeHelpers.PrepareConstrainedRegions ();
 145                                 try {}
 146                                 finally {
 147                                         if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
 148                                                 registered = success = true;
 149                                 }
 150                         } while (!registered);
 151                 }
 152
 153                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 154                 public IntPtr DangerousGetHandle ()
 155                 {
 156                         if (refcount <= 0){
 157                                 throw new ObjectDisposedException (GetType ().FullName);
 158                         }
 159
 160                         return handle;
 161                 }
 162
 163                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 164                 public void DangerousRelease ()
 165                 {
 166                         if (refcount <= 0)
 167                                 throw new ObjectDisposedException (GetType ().FullName);
 168
 169                         int newcount, current;
 170                         do {
 171                                 current = refcount;
 172                                 newcount = current-1;
 173                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
 174
 175                         if (newcount == 0 && owns_handle && !IsInvalid){
 176                                 ReleaseHandle ();
 177                                 handle = invalid_handle_value;
 178                         }
 179                 }
 180
 181                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 182                 public void Dispose ()
 183                 {
 184                         Dispose (true);
 185                         GC.SuppressFinalize (this);
 186                 }
 187
 188                 //
 189                 // See documentation, this invalidates the handle without
 190                 // closing it.
 191                 //
 192                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 193                 public void SetHandleAsInvalid ()
 194                 {
 195                         handle = invalid_handle_value;
 196                 }
 197
 198                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 199                 protected virtual void Dispose (bool disposing)
 200                 {
 201                         if (disposing)
 202                                 Close ();
 203                         else {
 204                                 //
 205                                 // The docs say `never call this with disposing=false',
 206                                 // the question is whether:
 207                                 //   * The runtime will ever call Dipose(false) for SafeHandles (special runtime case)
 208                                 //   * Whether we should just call ReleaseHandle regardless?
 209                                 //
 210                         }
 211                 }
 212
 213                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 214                 protected abstract bool ReleaseHandle ();
 215
 216                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 217                 protected void SetHandle (IntPtr handle)
 218                 {
 219                         this.handle = handle;
 220                 }
 221
 222                 public bool IsClosed {
 223                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 224                         get {
 225                                 return refcount <= 0;
 226                         }
 227                 }
 228
 229                 public abstract bool IsInvalid {
 230                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 231                         get;
 232                 }
 233
 234                 ~SafeHandle ()
 235                 {
 236                         if (owns_handle && !IsInvalid){
 237                                 ReleaseHandle ();
 238                                 handle = invalid_handle_value;
 239                         }
 240                 }
 241         }
 242 }