Add BasicWithKeyFileAttributeView interface

This new interface is similar to `BasicFileAttributeView` except it
gives implementations a hint that the fileKey() should be acquired
even at some performance cost.

`FileTreeWalker` uses this new interface to request a file key
in addition to regular file attributes so that file equality can
be efficiently performed when checking for loops during file
tree traversal.

This makes `FileTreeWalker` about 2x faster when traversing non
trivial file system trees with the FOLLOW_LINKS option.

Change-Id: I8de047c8fc241dbab9ad57c5e361118a3a94893d

(AKA JBR-3680 Cherry-pick Google's NIO patches to get faster file listing)

(cherry picked from commit 6d1c3f06c4)

src/java.base/share/classes/java/nio/file/FileTreeWalker.java

@@ -25,6 +25,8 @@
 
 package java.nio.file;
 
+import java.nio.file.attribute.BasicFileAttributeView;
+import java.nio.file.attribute.BasicWithKeyFileAttributeView;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.io.Closeable;
 import java.io.IOException;
@@ -217,7 +219,11 @@ class FileTreeWalker implements Closeable {
         // links then a link target might not exist so get attributes of link
         BasicFileAttributes attrs;
         try {
-            attrs = Files.readAttributes(file, BasicFileAttributes.class, linkOptions);
+            BasicFileAttributeView view = Files.getFileAttributeView(file, BasicWithKeyFileAttributeView.class, linkOptions);
+            if (view == null) {
+                view = Files.getFileAttributeView(file, BasicFileAttributeView.class, linkOptions);
+            }
+            attrs = view.readAttributes();
         } catch (IOException ioe) {
             if (!followLinks)
                 throw ioe;

src/java.base/share/classes/java/nio/file/attribute/BasicWithKeyFileAttributeView.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2007, 2011, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.nio.file.attribute;
+
+import java.io.IOException;
+
+/**
+ * Similar to {@link BasicFileAttributeView} with a hint to implementors
+ * to retrieve a valid {@link BasicFileAttributes#fileKey()} if possible, even
+ * at a performance cost.
+ */
+
+public interface BasicWithKeyFileAttributeView
+    extends BasicFileAttributeView {
+}

src/java.base/windows/classes/sun/nio/fs/WindowsFileAttributeViews.java

@@ -148,6 +148,23 @@ class WindowsFileAttributeViews {
         }
     }
 
+    private static class BasicWithKey extends Basic {
+        BasicWithKey(WindowsPath file, boolean followLinks) {
+            super(file, followLinks);
+        }
+
+        @Override
+        public WindowsFileAttributes readAttributes() throws IOException {
+            file.checkRead();
+            try {
+                return WindowsFileAttributes.getWithFileKey(file, followLinks);
+            } catch (WindowsException x) {
+                x.rethrowAsIOException(file);
+                return null;    // keep compiler happy
+            }
+        }
+    }
+
     static class Dos extends Basic implements DosFileAttributeView {
         private static final String READONLY_NAME = "readonly";
         private static final String ARCHIVE_NAME = "archive";
@@ -287,6 +304,10 @@ class WindowsFileAttributeViews {
         return new Basic(file, followLinks);
     }
 
+    static Basic createBasicWithKeyView(WindowsPath file, boolean followLinks) {
+        return new BasicWithKey(file, followLinks);
+    }
+
     static Dos createDosView(WindowsPath file, boolean followLinks) {
         return new Dos(file, followLinks);
     }

src/java.base/windows/classes/sun/nio/fs/WindowsFileAttributes.java

@@ -334,6 +334,15 @@ class WindowsFileAttributes
         }
 
         // file is reparse point so need to open file to get attributes
+        return getWithFileKey(path, followLinks);
+    }
+
+    /**
+     * Returns attributes of given file.
+     */
+    static WindowsFileAttributes getWithFileKey(WindowsPath path, boolean followLinks)
+        throws WindowsException
+    {
         long handle = path.openForReadAttributeAccess(followLinks);
         try {
             return readAttributes(handle);

src/java.base/windows/classes/sun/nio/fs/WindowsFileSystemProvider.java

@@ -166,6 +166,8 @@ class WindowsFileSystemProvider
         boolean followLinks = Util.followLinks(options);
         if (view == BasicFileAttributeView.class)
             return (V) WindowsFileAttributeViews.createBasicView(file, followLinks);
+        if (view == BasicWithKeyFileAttributeView.class)
+            return (V) WindowsFileAttributeViews.createBasicWithKeyView(file, followLinks);
         if (view == DosFileAttributeView.class)
             return (V) WindowsFileAttributeViews.createDosView(file, followLinks);
         if (view == AclFileAttributeView.class)
@@ -203,6 +205,8 @@ class WindowsFileSystemProvider
         boolean followLinks = Util.followLinks(options);
         if (name.equals("basic"))
             return WindowsFileAttributeViews.createBasicView(file, followLinks);
+        if (name.equals("basicwithkey"))
+            return WindowsFileAttributeViews.createBasicWithKeyView(file, followLinks);
         if (name.equals("dos"))
             return WindowsFileAttributeViews.createDosView(file, followLinks);
         if (name.equals("acl"))