Moving SafeDeleteContext and SafeFreeCredentials to common location

src/Common/src/System/Net/Security/Unix/SafeDeleteContext.cs

@@ -0,0 +1,46 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+
+namespace System.Net.Security
+{
+#if DEBUG
+    internal abstract class SafeDeleteContext : DebugSafeHandle
+    {
+#else
+    internal abstract class SafeDeleteContext : SafeHandle
+    {
+#endif
+        private SafeFreeCredentials _credential;
+
+        protected SafeDeleteContext(SafeFreeCredentials credential)
+            : base(IntPtr.Zero, true)
+        {
+            Debug.Assert((null != credential), "Invalid credential passed to SafeDeleteContext");
+
+            // When a credential handle is first associated with the context we keep credential
+            // ref count bumped up to ensure ordered finalization. The credential properties
+            // are used in the SSL/NEGO data structures and should survive the lifetime of
+            // the SSL/NEGO context
+            bool ignore = false;
+            _credential = credential;
+            _credential.DangerousAddRef(ref ignore);
+        }
+
+        public override bool IsInvalid
+        {
+            get { return (null == _credential); }
+        }
+
+        protected override bool ReleaseHandle()
+        {
+            Debug.Assert((null != _credential), "Null credential in SafeDeleteContext");
+            _credential.DangerousRelease();
+            _credential = null;
+            return true;
+        }
+    }
+}