mcs/class/referencesource/System.Web/Util/GCUtil.cs

   1 //------------------------------------------------------------------------------
   2 // <copyright file="GCUtil.cs" company="Microsoft">
   3 //     Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 //------------------------------------------------------------------------------
   6
   7 namespace System.Web.Util {
   8     using System;
   9     using System.Runtime.InteropServices;
  10     using System.Security.Permissions;
  11
  12     // Provides helper methods for wrapping managed objects so that they can be passed to and from unmanaged code.
  13     // Unmanaged code can't actually inspect these objects at all since they're just GCHandles. And these handles
  14     // cannot be reused (they're single-shot).
  15
  16     [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]
  17     internal static class GCUtil {
  18
  19         public static IntPtr RootObject(object obj) {
  20             return (obj != null)
  21                 ? (IntPtr)GCHandle.Alloc(obj)
  22                 : IntPtr.Zero;
  23         }
  24
  25         public static object UnrootObject(IntPtr pointer) {
  26             if (pointer != IntPtr.Zero) {
  27                 GCHandle gcHandle = (GCHandle)pointer;
  28                 if (gcHandle.IsAllocated) {
  29                     object target = gcHandle.Target;
  30                     gcHandle.Free();
  31                     return target;
  32                 }
  33             }
  34
  35             return null;
  36         }
  37
  38     }
  39
  40     // This wrapper around a managed object is opaque to SizedReference GC handle
  41     // and therefore helps with calculating size of only relevant graph of objects
  42     internal class DisposableGCHandleRef<T> : IDisposable
  43     where T : class, IDisposable {
  44         GCHandle _handle;
  45         [PermissionSet(SecurityAction.Assert, Unrestricted = true)]
  46         public DisposableGCHandleRef(T t) {
  47             Debug.Assert(t != null);
  48             _handle = GCHandle.Alloc(t);
  49         }
  50
  51         public T Target {
  52             [PermissionSet(SecurityAction.Assert, Unrestricted = true)]
  53             get {
  54                 Debug.Assert(_handle.IsAllocated);
  55                 return (T)_handle.Target;
  56             }
  57         }
  58
  59         [PermissionSet(SecurityAction.Assert, Unrestricted = true)]
  60         public void Dispose() {
  61             Target.Dispose();
  62             Debug.Assert(_handle.IsAllocated);
  63             if (_handle.IsAllocated) {
  64                 _handle.Free();
  65             }
  66         }
  67     }
  68 }