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 #if NET_2_0
  47 using System;
  48 using System.Runtime.InteropServices;
  49 using System.Runtime.ConstrainedExecution;
  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                 protected SafeHandle (IntPtr invalidHandleValue, bool ownsHandle)
  66                 {
  67                         invalid_handle_value = invalidHandleValue;
  68                         owns_handle = ownsHandle;
  69                         refcount = 1;
  70                 }
  71
  72                 public void Close ()
  73                 {
  74                         if (refcount == 0)
  75                                 throw new ObjectDisposedException (GetType ().FullName);
  76
  77                         int newcount, current;
  78                         do {
  79                                 current = refcount;
  80                                 newcount = current-1;
  81                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
  82
  83                         if (newcount == 0 && owns_handle){
  84                                 ReleaseHandle ();
  85                                 handle = invalid_handle_value;
  86                         }
  87                 }
  88
  89                 //
  90                 // I do not know when we could not be able to increment the
  91                 // reference count and set success to false.   It might just
  92                 // be a convention used for the following code pattern:
  93                 //
  94                 // bool release = false
  95                 // try { x.DangerousAddRef (ref release); ... }
  96                 // finally { if (release) x.DangerousRelease (); }
  97                 //
  98                 public void DangerousAddRef (ref bool success)
  99                 {
 100                         if (refcount == 0)
 101                                 throw new ObjectDisposedException (GetType ().FullName);
 102
 103                         int newcount, current;
 104                         do {
 105                                 current = refcount;
 106                                 newcount = current + 1;
 107
 108                                 if (handle == invalid_handle_value || current == 0){
 109                                         //
 110                                         // In MS, calling sf.Close () followed by a call
 111                                         // to P/Invoke with SafeHandles throws this, but
 112                                         // am left wondering: when would "success" be
 113                                         // set to false?
 114                                         //
 115                                         throw new ObjectDisposedException (GetType ().FullName);
 116                                 }
 117                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
 118                         success = true;
 119                 }
 120
 121                 public IntPtr DangerousGetHandle ()
 122                 {
 123                         if (refcount == 0){
 124                                 throw new ObjectDisposedException (GetType ().FullName);
 125                         }
 126
 127                         return handle;
 128                 }
 129
 130                 public void DangerousRelease ()
 131                 {
 132                         if (refcount == 0)
 133                                 throw new ObjectDisposedException (GetType ().FullName);
 134
 135                         int newcount, current;
 136                         do {
 137                                 current = refcount;
 138                                 newcount = current-1;
 139                         } while (Interlocked.CompareExchange (ref refcount, newcount, current) != current);
 140
 141                         if (newcount == 0 && owns_handle){
 142                                 ReleaseHandle ();
 143                                 handle = invalid_handle_value;
 144                         }
 145                 }
 146
 147                 public virtual void Dispose ()
 148                 {
 149                         Dispose (true);
 150                         GC.SuppressFinalize (this);
 151                 }
 152
 153                 //
 154                 // See documentation, this invalidates the handle without
 155                 // closing it.
 156                 //
 157                 public void SetHandleAsInvalid ()
 158                 {
 159                         handle = invalid_handle_value;
 160                 }
 161
 162                 protected virtual void Dispose (bool disposing)
 163                 {
 164                         if (disposing)
 165                                 Close ();
 166                         else {
 167                                 //
 168                                 // The docs say `never call this with disposing=false',
 169                                 // the question is whether:
 170                                 //   * The runtime will ever call Dipose(false) for SafeHandles (special runtime case)
 171                                 //   * Whether we should just call ReleaseHandle regardless?
 172                                 //
 173                         }
 174                 }
 175
 176                 protected abstract bool ReleaseHandle ();
 177
 178                 protected void SetHandle (IntPtr handle)
 179                 {
 180                         this.handle = handle;
 181                 }
 182
 183                 public bool IsClosed {
 184                         get {
 185                                 return refcount == 0;
 186                         }
 187                 }
 188
 189                 public abstract bool IsInvalid {
 190                         get;
 191                 }
 192
 193                 ~SafeHandle ()
 194                 {
 195                         if (owns_handle){
 196                                 ReleaseHandle ();
 197                                 handle = invalid_handle_value;
 198                         }
 199                 }
 200         }
 201 }
 202 #endif