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

   1 //------------------------------------------------------------------------------
   2 // <copyright file="PinnedArraySegment.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.Diagnostics.CodeAnalysis;
  10     using System.Runtime.InteropServices;
  11     using System.Security.Permissions;
  12
  13     // Utility class for pinning an ArraySegment<T> so that it can be passed to unmanaged code.
  14     //
  15     // This type is not thread safe.
  16
  17     [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]
  18     internal sealed class PinnedArraySegment<T> : IDisposable {
  19
  20         private int _count;
  21         private GCHandle _gcHandle;
  22
  23         [SuppressMessage("Microsoft.Reliability", "CA2006:UseSafeHandleToEncapsulateNativeResources", Justification = @"This is a memory pointer, not a handle. The handle is in the _gcHandle field, and its lifetime is controlled by the caller.")]
  24         private IntPtr _pointer;
  25
  26         internal unsafe PinnedArraySegment(ArraySegment<T> segment) {
  27             // Structs - like ArraySegment<T> - can be "torn" by malicious users trying to take
  28             // advantage of race conditions that occur as a result of their copy-by-value semantics.
  29             // Since we'll pass the ArraySegment<T> to unmanaged code, we need to perform validation
  30             // to make sure that this hasn't happened. The ArraySegment<T> constructor can be used
  31             // to perform this validation. (MSRC 10170)
  32             segment = new ArraySegment<T>(segment.Array, segment.Offset, segment.Count);
  33
  34             _gcHandle = GCHandle.Alloc(segment.Array, GCHandleType.Pinned); // pin the array so that unmanaged code can access it
  35             _pointer = Marshal.UnsafeAddrOfPinnedArrayElement(segment.Array, segment.Offset);
  36             _count = segment.Count;
  37         }
  38
  39         public int Count {
  40             get {
  41                 ThrowIfDisposed();
  42                 return _count;
  43             }
  44         }
  45
  46         public IntPtr Pointer {
  47             get {
  48                 ThrowIfDisposed();
  49                 return _pointer;
  50             }
  51         }
  52
  53         [SuppressMessage("Microsoft.Usage", "CA2216:DisposableTypesShouldDeclareFinalizer", Justification = @"We don't own native resources.")]
  54         public void Dispose() {
  55             if (_pointer != IntPtr.Zero) {
  56                 // only free the GCHandle once
  57                 _pointer = IntPtr.Zero;
  58                 _gcHandle.Free();
  59             }
  60         }
  61
  62         private void ThrowIfDisposed() {
  63             if (_pointer == IntPtr.Zero) {
  64                 throw new ObjectDisposedException(GetType().FullName);
  65             }
  66         }
  67
  68     }
  69 }