Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System/sys/system/EnvironmentHelpers.cs

@@ -0,0 +1,57 @@
+using System.ComponentModel;
+using System.Security;
+using System.Security.Permissions;
+using System.Security.Principal;
+using Microsoft.Win32;
+using Microsoft.Win32.SafeHandles;
+
+namespace System
+{
+    internal static class EnvironmentHelpers
+    {
+        private static volatile bool s_IsAppContainerProcess;
+        private static volatile bool s_IsAppContainerProcessInitalized;
+
+        public static bool IsAppContainerProcess {
+            get {
+                if(!s_IsAppContainerProcessInitalized) {
+                   if(Environment.OSVersion.Platform != PlatformID.Win32NT) {
+                       s_IsAppContainerProcess = false;
+                   } else if(Environment.OSVersion.Version.Major < 6 || (Environment.OSVersion.Version.Major == 6 && Environment.OSVersion.Version.Minor <= 1)) {
+                       // Windows 7 or older.
+                       s_IsAppContainerProcess = false;
+                   } else {
+                       s_IsAppContainerProcess = HasAppContainerToken();
+                   }
+
+                    s_IsAppContainerProcessInitalized = true;
+                }
+
+                return s_IsAppContainerProcess;
+            }
+        }
+
+        [SecuritySafeCritical]
+        [SecurityPermission(SecurityAction.Assert, Flags = SecurityPermissionFlag.UnmanagedCode | SecurityPermissionFlag.ControlPrincipal)]
+        private static unsafe bool HasAppContainerToken() {
+            int* dwIsAppContainerPtr = stackalloc int[1];
+            uint dwLength = 0;
+
+            using (WindowsIdentity wi = WindowsIdentity.GetCurrent(TokenAccessLevels.Query)) {
+                if (!UnsafeNativeMethods.GetTokenInformation(wi.Token, UnsafeNativeMethods.TokenIsAppContainer, new IntPtr(dwIsAppContainerPtr), sizeof(int), out dwLength)) {
+                    throw new Win32Exception();
+                }
+            }
+
+            return (*dwIsAppContainerPtr != 0);
+        }
+
+        internal static bool IsWindowsVistaOrAbove()
+        {
+            // Method should match the logic of the internal Environment.IsWindowsVista property in mscorlib
+            // If this method turns out to be heavily used we might want to cache at least part of this value.
+            OperatingSystem os = Environment.OSVersion;
+            return os.Platform == PlatformID.Win32NT && os.Version.Major >= 6;
+        }
+    }
+}