Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.ServiceModel/System/ServiceModel/Channels/SafeNativeMethods.cs

@@ -0,0 +1,46 @@
+//------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//------------------------------------------------------------
+namespace System.ServiceModel.Channels
+{
+    using System.Runtime;
+    using System.Runtime.InteropServices;
+    using System.Runtime.Versioning;
+    using System.Security;
+
+    [SuppressUnmanagedCodeSecurity]
+    internal static class SafeNativeMethods
+    {
+        public const string KERNEL32 = "kernel32.dll";
+
+        [DllImport(KERNEL32, SetLastError = false)]
+        [ResourceExposure(ResourceScope.None)]
+        static extern uint GetSystemTimeAdjustment(
+            [Out] out int adjustment,
+            [Out] out uint increment,
+            [Out] out uint adjustmentDisabled
+        );
+
+        [DllImport(KERNEL32, SetLastError = true)]
+        [ResourceExposure(ResourceScope.None)]
+        public static extern void GetSystemTimeAsFileTime(out long time);
+
+        [Fx.Tag.SecurityNote(Critical = "Calls critical method GetSystemTimeAdjustment.",
+            Safe = "Method is a SafeNativeMethod.")]
+        [SecuritySafeCritical]
+        internal static long GetSystemTimeResolution()
+        {
+            int dummyAdjustment;
+            uint increment;
+            uint dummyAdjustmentDisabled;
+
+            if (GetSystemTimeAdjustment(out dummyAdjustment, out increment, out dummyAdjustmentDisabled) != 0)
+            {
+                return (long)increment;
+            }
+
+            // Assume the default, which is around 15 milliseconds.
+            return 15 * TimeSpan.TicksPerMillisecond;
+        }
+    }
+}