8213406: (fs) More than one instance of built-in FileSystem observed in heap

Reviewed-by: alanb, cushon, weijun

src/java.base/macosx/classes/sun/nio/fs/BsdFileSystemProvider.java

@@ -31,7 +31,7 @@ import java.io.IOException;
  * Bsd implementation of FileSystemProvider
  */
 
-public class BsdFileSystemProvider extends UnixFileSystemProvider {
+class BsdFileSystemProvider extends UnixFileSystemProvider {
     public BsdFileSystemProvider() {
         super();
     }

src/java.base/macosx/classes/sun/nio/fs/DefaultFileSystemProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2018, 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
@@ -25,19 +25,29 @@
 
 package sun.nio.fs;
 
-import java.nio.file.spi.FileSystemProvider;
+import java.nio.file.FileSystem;
 
 /**
  * Creates this platform's default FileSystemProvider.
  */
 
 public class DefaultFileSystemProvider {
+    private static final MacOSXFileSystemProvider INSTANCE
+        = new MacOSXFileSystemProvider();
+
     private DefaultFileSystemProvider() { }
 
     /**
-     * Returns the default FileSystemProvider.
+     * Returns the platform's default file system provider.
      */
-    public static FileSystemProvider create() {
-        return new MacOSXFileSystemProvider();
+    public static MacOSXFileSystemProvider instance() {
+        return INSTANCE;
+    }
+
+    /**
+     * Returns the platform's default file system.
+     */
+    public static FileSystem theFileSystem() {
+        return INSTANCE.theFileSystem();
     }
 }

src/java.base/macosx/classes/sun/nio/fs/MacOSXFileSystemProvider.java

@@ -34,7 +34,7 @@ import sun.security.action.GetPropertyAction;
  * MacOSX implementation of FileSystemProvider
  */
 
-public class MacOSXFileSystemProvider extends BsdFileSystemProvider {
+class MacOSXFileSystemProvider extends BsdFileSystemProvider {
     public MacOSXFileSystemProvider() {
         super();
     }