--- old/src/java.base/windows/classes/java/io/WinNTFileSystem.java	2018-03-12 11:23:26.000000000 -0700
+++ new/src/java.base/windows/classes/java/io/WinNTFileSystem.java	2018-03-12 11:23:25.000000000 -0700
@@ -43,7 +43,8 @@
     private final char slash;
     private final char altSlash;
     private final char semicolon;
-    private final String userDir;
+    private String userDir;
+    private volatile boolean isUserDirNormal;
 
     public WinNTFileSystem() {
         Properties props = GetPropertyAction.privilegedGetProperties();
@@ -353,7 +354,17 @@
         if (sm != null) {
             sm.checkPropertyAccess("user.dir");
         }
-        return normalize(userDir);
+        boolean normalize = !isUserDirNormal;
+        if (normalize) {
+            synchronized(userDir) {
+                normalize = !isUserDirNormal;
+                if (normalize) {
+                    userDir = normalize(userDir);
+                    isUserDirNormal = true;
+                }
+            }
+        }
+        return userDir;
     }
 
     private String getDrive(String path) {