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 // On implementing SafeHandles:
  34 //     http://blogs.msdn.com/bclteam/archive/2005/03/15/396335.aspx
  35 //
  36 // Issues:
  37 //     The System.Runtime.ConstrainedExecution.ReliabilityContractAttribute has
  38 //     not been applied to any APIs here yet.
  39 //
  40 //     TODO: Although DangerousAddRef has been implemented, I need to
  41 //     find out whether the runtime performs the P/Invoke if the
  42 //     handle has been disposed already.
  43 //
  44 //
  45
  46 using System;
  47 using System.Runtime.InteropServices;
  48 using System.Runtime.ConstrainedExecution;
  49 using System.Runtime.CompilerServices;
  50 using System.Threading;
  51
  52 namespace System.Runtime.InteropServices
  53 {
  54         public abstract class SafeHandle : CriticalFinalizerObject, IDisposable {
  55                 //
  56                 // Warning: the offset of handle is mapped inside the runtime
  57                 // if you move this, you must updated the runtime definition of
  58                 // MonoSafeHandle
  59                 //
  60                 protected IntPtr handle;
  61                 IntPtr invalid_handle_value;
  62                 int refcount = 0;
  63                 bool owns_handle;
  64
  65 #if NET_2_1
  66                 protected SafeHandle ()
  67                 {
  68                         throw new NotImplementedException ();
  69                 }
  70 #endif
  71                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.MayFail)]
  72                 protected SafeHandle (IntPtr invalidHandleValue, bool ownsHandle)
  73                 {
  74                         invalid_handle_value = invalidHandleValue;
  75                         owns_handle = ownsHandle;
  76                         refcount = 1;
  77                 }
  78
  79                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
  80                 public void Close ()
  81                 {
  82                         if (refcount == 0)
  83                                 throw new ObjectDisposedException (GetType ().FullName);
  84
  85                         int newcount = 0, current = 0;
  86                         bool registered = false;
  87                         RuntimeHelpers.PrepareConstrainedRegions ();
  88                         try {
  89                                 do {
  90                                         current = refcount;
  91                                         newcount = current-1;
  92
  93                                         try {}
  94                                         finally {
  95                                                 if (Interlocked.CompareExchange (ref refcount, newcount, current) == current)
  96                                                         registered = true;
  97                                         }
  98                                 } while (!registered);
  99                         } finally {
 100                                 if (registered && newcount == 0 && owns_handle && !IsInvalid){
 101                                         ReleaseHandle ();
 102                                         handle = invalid_handle_value;
 103                                         refcount = -1;
 104                                 }
 105                         }
 106                 }
 107
 108                 //
 109                 // I do not know when we could not be able to increment the
 110                 // reference count and set success to false.   It might just
 111                 // be a convention used for the following code pattern:
 112                 //
 113                 // bool release = false
 114                 // try { x.DangerousAddRef (ref release); ... }
 115                 // finally { if (release) x.DangerousRelease (); }
 116                 //
 117                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.MayFail)]
 118                 public void DangerousAddRef (ref bool success)
 119                 {
 120                         if (refcount <= 0)
 121                                 throw new ObjectDisposedException (GetType ().FullName);
 122
 123                         int newcount, current;
 124                         do {
 125                                 current = refcount;
 126                                 newcount = current + 1;
 127
 128                                 if (current <= 0){
 129                                         //
 130                                         // In MS, calling sf.Close () followed by a call
 131                                         // to P/Invoke with SafeHandles throws this, but
 132                                         // am left wondering: when would "success" be
 133                                         // set to false?
 134                                         //
 135                                         throw new ObjectDisposedException (GetType ().FullName);
 136                                 }
 137                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
 138                         success = true;
 139                 }
 140
 141                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 142                 public IntPtr DangerousGetHandle ()
 143                 {
 144                         if (refcount <= 0){
 145                                 throw new ObjectDisposedException (GetType ().FullName);
 146                         }
 147
 148                         return handle;
 149                 }
 150
 151                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 152                 public void DangerousRelease ()
 153                 {
 154                         if (refcount <= 0)
 155                                 throw new ObjectDisposedException (GetType ().FullName);
 156
 157                         int newcount, current;
 158                         do {
 159                                 current = refcount;
 160                                 newcount = current-1;
 161                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
 162
 163                         if (newcount == 0 && owns_handle && !IsInvalid){
 164                                 ReleaseHandle ();
 165                                 handle = invalid_handle_value;
 166                         }
 167                 }
 168
 169                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 170                 public void Dispose ()
 171                 {
 172                         Dispose (true);
 173                         GC.SuppressFinalize (this);
 174                 }
 175
 176                 //
 177                 // See documentation, this invalidates the handle without
 178                 // closing it.
 179                 //
 180                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 181                 public void SetHandleAsInvalid ()
 182                 {
 183                         handle = invalid_handle_value;
 184                 }
 185
 186                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 187                 protected virtual void Dispose (bool disposing)
 188                 {
 189                         if (disposing)
 190                                 Close ();
 191                         else {
 192                                 //
 193                                 // The docs say `never call this with disposing=false',
 194                                 // the question is whether:
 195                                 //   * The runtime will ever call Dipose(false) for SafeHandles (special runtime case)
 196                                 //   * Whether we should just call ReleaseHandle regardless?
 197                                 //
 198                         }
 199                 }
 200
 201                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 202                 protected abstract bool ReleaseHandle ();
 203
 204                 [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 205                 protected void SetHandle (IntPtr handle)
 206                 {
 207                         this.handle = handle;
 208                 }
 209
 210                 public bool IsClosed {
 211                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 212                         get {
 213                                 return refcount <= 0;
 214                         }
 215                 }
 216
 217                 public abstract bool IsInvalid {
 218                         [ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
 219                         get;
 220                 }
 221
 222                 ~SafeHandle ()
 223                 {
 224                         if (owns_handle && !IsInvalid){
 225                                 ReleaseHandle ();
 226                                 handle = invalid_handle_value;
 227                         }
 228                 }
 229         }
 230 }