Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

mcs/class/corlib/ReferenceSources/ExecutionContext.cs

@@ -0,0 +1,56 @@
+
+using System.Security;
+
+namespace System.Threading
+{
+	partial class ExecutionContext
+	{
+		internal static ExecutionContext Capture (ref StackCrawlMark stackMark, CaptureOptions options)
+		{
+			return Capture ((options & CaptureOptions.IgnoreSyncCtx) == 0, false);
+		}
+
+		internal static ExecutionContext FastCapture()
+		{
+			return Capture ();
+		}
+
+		[Flags]
+		internal enum CaptureOptions
+		{
+			None = 0x00,
+
+			IgnoreSyncCtx = 0x01,       //Don't flow SynchronizationContext
+
+			OptimizeDefaultCase = 0x02, //Faster in the typical case, but can't show the result to users
+			                            // because they could modify the shared default EC.
+			                            // Use this only if you won't be exposing the captured EC to users.
+		}
+
+		private static readonly ExecutionContext s_dummyDefaultEC = new ExecutionContext();
+		static internal ExecutionContext PreAllocatedDefault
+		{
+			[SecuritySafeCritical]
+			get {
+				return s_dummyDefaultEC;
+			}
+		}
+
+		internal bool IsPreAllocatedDefault
+		{
+			get
+			{
+				return this == s_dummyDefaultEC;
+			}
+		}
+	}
+
+	[Serializable]
+	internal enum StackCrawlMark
+	{
+		LookForMe = 0,
+		LookForMyCaller = 1,
+		LookForMyCallersCaller = 2,
+		LookForThread = 3
+	}
+}