Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

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+//------------------------------------------------------------------------------
+// <copyright file="PinnedArraySegment.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Diagnostics.CodeAnalysis;
+    using System.Runtime.InteropServices;
+    using System.Security.Permissions;
+
+    // Utility class for pinning an ArraySegment<T> so that it can be passed to unmanaged code.
+    //
+    // This type is not thread safe.
+
+    [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]
+    internal sealed class PinnedArraySegment<T> : IDisposable {
+
+        private int _count;
+        private GCHandle _gcHandle;
+
+        [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.")]
+        private IntPtr _pointer;
+
+        internal unsafe PinnedArraySegment(ArraySegment<T> segment) {
+            // Structs - like ArraySegment<T> - can be "torn" by malicious users trying to take
+            // advantage of race conditions that occur as a result of their copy-by-value semantics.
+            // Since we'll pass the ArraySegment<T> to unmanaged code, we need to perform validation
+            // to make sure that this hasn't happened. The ArraySegment<T> constructor can be used
+            // to perform this validation. (MSRC 10170)
+            segment = new ArraySegment<T>(segment.Array, segment.Offset, segment.Count);
+
+            _gcHandle = GCHandle.Alloc(segment.Array, GCHandleType.Pinned); // pin the array so that unmanaged code can access it
+            _pointer = Marshal.UnsafeAddrOfPinnedArrayElement(segment.Array, segment.Offset);
+            _count = segment.Count;
+        }
+
+        public int Count {
+            get {
+                ThrowIfDisposed();
+                return _count;
+            }
+        }
+
+        public IntPtr Pointer {
+            get {
+                ThrowIfDisposed();
+                return _pointer;
+            }
+        }
+
+        [SuppressMessage("Microsoft.Usage", "CA2216:DisposableTypesShouldDeclareFinalizer", Justification = @"We don't own native resources.")]
+        public void Dispose() {
+            if (_pointer != IntPtr.Zero) {
+                // only free the GCHandle once
+                _pointer = IntPtr.Zero;
+                _gcHandle.Free();
+            }
+        }
+
+        private void ThrowIfDisposed() {
+            if (_pointer == IntPtr.Zero) {
+                throw new ObjectDisposedException(GetType().FullName);
+            }
+        }
+
+    }
+}