Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data/System/Data/Odbc/OdbcEnvironment.cs

@@ -0,0 +1,46 @@
+//------------------------------------------------------------------------------
+// <copyright file="OdbcEnvironment.cs" company="Microsoft">
+//      Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+// <owner current="true" primary="true">[....]</owner>
+// <owner current="true" primary="false">[....]</owner>
+//------------------------------------------------------------------------------
+
+using System;
+using System.Data;
+using System.Data.Common;
+using System.Threading;
+
+
+namespace System.Data.Odbc {
+    sealed internal class OdbcEnvironment {
+        static private object _globalEnvironmentHandle;
+        static private object _globalEnvironmentHandleLock = new object();
+
+        private OdbcEnvironment () {}  // default const.
+        
+        static internal OdbcEnvironmentHandle GetGlobalEnvironmentHandle() {
+            OdbcEnvironmentHandle globalEnvironmentHandle = _globalEnvironmentHandle as OdbcEnvironmentHandle;
+            if(null == globalEnvironmentHandle) {
+                ADP.CheckVersionMDAC(true);
+                
+                lock(_globalEnvironmentHandleLock) {
+                    globalEnvironmentHandle = _globalEnvironmentHandle as OdbcEnvironmentHandle;
+                    if(null == globalEnvironmentHandle) {
+                        globalEnvironmentHandle = new OdbcEnvironmentHandle();
+                        _globalEnvironmentHandle = globalEnvironmentHandle;
+                    }
+                }
+            }
+            return globalEnvironmentHandle;
+        }
+
+        static internal void ReleaseObjectPool() {
+            object globalEnvironmentHandle = Interlocked.Exchange(ref _globalEnvironmentHandle, null);
+            if(null != globalEnvironmentHandle) {
+                (globalEnvironmentHandle as OdbcEnvironmentHandle).Dispose(); // internally refcounted so will happen correctly
+            }
+        }
+    }
+}
+