8236661: launcher test PatchSystemModules.java start failing frequent…

…ly after JDK-8234049

Reviewed-by: alanb, mchung

src/java.base/share/classes/sun/nio/ch/FileChannelImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -49,6 +49,7 @@
 import jdk.internal.access.SharedSecrets;
 import jdk.internal.misc.ExtendedMapMode;
 import jdk.internal.misc.Unsafe;
+import jdk.internal.misc.VM;
 import jdk.internal.ref.Cleaner;
 import jdk.internal.ref.CleanerFactory;
 
@@ -1116,8 +1117,11 @@ private Unmapper mapInternal(MapMode mode, long position, long size, int prot, b
     }
 
     private boolean isSync(MapMode mode) {
-        return mode == ExtendedMapMode.READ_ONLY_SYNC ||
-                mode == ExtendedMapMode.READ_WRITE_SYNC;
+        // Do not want to initialize ExtendedMapMode until
+        // after the module system has been initialized
+        return !VM.isModuleSystemInited() ? false :
+            (mode == ExtendedMapMode.READ_ONLY_SYNC ||
+                mode == ExtendedMapMode.READ_WRITE_SYNC);
     }
 
     private int toProt(MapMode mode) {