Significantly speed up FileTreeIterator on Windows

Getting attributes of files on Windows is an expensive operation.
Windows stores file attributes in the directory, so they are
basically available "for free" when a directory is listed. The
implementation of Java's Files.walkFileTree() takes advantage of
that (at least in the OpenJDK implementation for Windows) and
provides the attributes from the directory to a FileVisitor.

Using Files.walkFileTree() with a maximum depth of 1 is thus a
good approach on Windows to get both the file names and the
attributes in one go.

In my tests, this gives a significant speed-up of FileTreeIterator
over the "normal" way: using File.listFiles() and then reading the
attributes of each file individually. The speed-up is hard to
quantify exactly, but in my tests I've observed consistently 30-40%
for staging 500 files one after another, each individually, and up
to 50% for individual TreeWalks with a FileTreeIterator.

On Unix, this technique is detrimental. Unix stores file attributes
differently, and getting attributes of individual files is not costly.
On Unix, the old way of doing a listFiles() and getting individual
attributes (both native operations) is about three times faster than
using walkFileTree, which is implemented in Java.

Therefore, move the operation to FS/FS_Win32 and call it from
FileTreeIterator, so that we can have different implementations
depending on the file system.

A little performance test program is included as a JUnit test (to be
run manually).

While this does speed up things on Windows, it doesn't solve the basic
problem of bug 532300: the iterator always gets the full directory
listing and the attributes of all files, and the more files there are
the longer that takes.

Bug: 532300
Change-Id: Ic5facb871c725256c2324b0d97b95e6efc33282a
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit.test/exttst/org/eclipse/jgit/treewalk/FileTreeIteratorPerformanceTest.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2018, Thomas Wolf <thomas.wolf@paranor.ch>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.treewalk;
+
+import static org.junit.Assert.fail;
+
+import org.eclipse.jgit.api.Git;
+import org.eclipse.jgit.junit.RepositoryTestCase;
+import org.eclipse.jgit.treewalk.filter.PathFilter;
+import org.junit.Test;
+
+/**
+ * Simple performance test for git add / FileTreeIterator.
+ */
+public class FileTreeIteratorPerformanceTest extends RepositoryTestCase {
+
+	private static int N_OF_FILES = 501;
+
+	@Test
+	public void testPerformance() throws Exception {
+		try (Git git = new Git(db)) {
+			long times[] = new long[N_OF_FILES];
+			long sum = 0;
+			String lastName = null;
+			for (int i = 0; i < N_OF_FILES; i++) {
+				lastName = "a" + (i + 100000) + ".txt";
+				writeTrashFile(lastName, "");
+				long start = System.nanoTime();
+				git.add().addFilepattern(lastName).call();
+				long elapsed = System.nanoTime() - start;
+				times[i] = elapsed;
+				sum += elapsed;
+			}
+			System.out.println("Total (µs) " + sum / 1000.0);
+			for (int i = 0; i < times.length; i++) {
+				System.out
+						.println("Time " + i + " (µs) = " + times[i] / 1000.0);
+			}
+			FileTreeIterator iter = new FileTreeIterator(db);
+			try (TreeWalk walk = new TreeWalk(db)) {
+				walk.setFilter(PathFilter.create(lastName));
+				walk.addTree(iter);
+				long start = System.nanoTime();
+				if (walk.next()) {
+					System.out.println("Walk time (µs) = "
+							+ (System.nanoTime() - start) / 1000.0);
+				} else {
+					fail("File not found");
+				}
+			}
+		}
+	}
+}

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/FileTreeIterator.java

@@ -211,13 +211,7 @@ public class FileTreeIterator extends WorkingTreeIterator {
 	}
 
 	private Entry[] entries() {
-		final File[] all = directory.listFiles();
-		if (all == null)
-			return EOF;
-		final Entry[] r = new Entry[all.length];
-		for (int i = 0; i < r.length; i++)
-			r[i] = new FileEntry(all[i], fs, fileModeStrategy);
-		return r;
+		return fs.list(directory, fileModeStrategy);
 	}
 
 	/**
@@ -246,7 +240,7 @@ public class FileTreeIterator extends WorkingTreeIterator {
 	 *
 	 * @since 4.3
 	 */
-	static public class DefaultFileModeStrategy implements FileModeStrategy {
+	public static class DefaultFileModeStrategy implements FileModeStrategy {
 		/**
 		 * a singleton instance of the default FileModeStrategy
 		 */
@@ -279,7 +273,7 @@ public class FileTreeIterator extends WorkingTreeIterator {
 	 *
 	 * @since 4.3
 	 */
-	static public class NoGitlinksStrategy implements FileModeStrategy {
+	public static class NoGitlinksStrategy implements FileModeStrategy {
 
 		/**
 		 * a singleton instance of the default FileModeStrategy
@@ -304,7 +298,7 @@ public class FileTreeIterator extends WorkingTreeIterator {
 	/**
 	 * Wrapper for a standard Java IO file
 	 */
-	static public class FileEntry extends Entry {
+	public static class FileEntry extends Entry {
 		private final FileMode mode;
 
 		private FS.Attributes attributes;
@@ -343,6 +337,29 @@ public class FileTreeIterator extends WorkingTreeIterator {
 			mode = fileModeStrategy.getMode(f, attributes);
 		}
 
+		/**
+		 * Create a new file entry given the specified FileModeStrategy
+		 *
+		 * @param f
+		 *            file
+		 * @param fs
+		 *            file system
+		 * @param attributes
+		 *            of the file
+		 * @param fileModeStrategy
+		 *            the strategy to use when determining the FileMode of a
+		 *            file; controls gitlinks etc.
+		 *
+		 * @since 5.0
+		 */
+		public FileEntry(File f, FS fs, FS.Attributes attributes,
+				FileModeStrategy fileModeStrategy) {
+			this.fs = fs;
+			this.attributes = attributes;
+			f = fs.normalize(f);
+			mode = fileModeStrategy.getMode(f, attributes);
+		}
+
 		@Override
 		public FileMode getMode() {
 			return mode;
@@ -365,13 +382,13 @@ public class FileTreeIterator extends WorkingTreeIterator {
 
 		@Override
 		public InputStream openInputStream() throws IOException {
-			if (fs.isSymLink(getFile()))
+			if (attributes.isSymbolicLink()) {
 				return new ByteArrayInputStream(fs.readSymLink(getFile())
-						.getBytes(
-						Constants.CHARACTER_ENCODING));
-			else
+						.getBytes(Constants.CHARACTER_ENCODING));
+			} else {
 				return new FileInputStream(getFile());
 			}
+		}
 
 		/**
 		 * Get the underlying file of this entry.

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java

@@ -1165,8 +1165,12 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 		return contentDigest.digest();
 	}
 
-	/** A single entry within a working directory tree. */
-	protected static abstract class Entry {
+	/**
+	 * A single entry within a working directory tree.
+	 *
+	 * @since 5.0
+	 */
+	public static abstract class Entry {
 		byte[] encodedName;
 
 		int encodedNameLen;

org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java

@@ -71,6 +71,9 @@ import org.eclipse.jgit.errors.CommandFailedException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.treewalk.FileTreeIterator.FileEntry;
+import org.eclipse.jgit.treewalk.FileTreeIterator.FileModeStrategy;
+import org.eclipse.jgit.treewalk.WorkingTreeIterator.Entry;
 import org.eclipse.jgit.util.ProcessResult.Status;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -81,6 +84,14 @@ import org.slf4j.LoggerFactory;
 public abstract class FS {
 	private static final Logger LOG = LoggerFactory.getLogger(FS.class);
 
+	/**
+	 * An empty array of entries, suitable as a return value for
+	 * {@link #list(File, FileModeStrategy)}.
+	 *
+	 * @since 5.0
+	 */
+	protected static final Entry[] NO_ENTRIES = {};
+
 	/**
 	 * This class creates FS instances. It will be overridden by a Java7 variant
 	 * if such can be detected in {@link #detect(Boolean)}.
@@ -886,6 +897,29 @@ public abstract class FS {
 		return FileUtils.relativizePath(base, other, File.separator, this.isCaseSensitive());
 	}
 
+	/**
+	 * Enumerates children of a directory.
+	 *
+	 * @param directory
+	 *            to get the children of
+	 * @param fileModeStrategy
+	 *            to use to calculate the git mode of a child
+	 * @return an array of entries for the children
+	 *
+	 * @since 5.0
+	 */
+	public Entry[] list(File directory, FileModeStrategy fileModeStrategy) {
+		final File[] all = directory.listFiles();
+		if (all == null) {
+			return NO_ENTRIES;
+		}
+		final Entry[] result = new Entry[all.length];
+		for (int i = 0; i < result.length; i++) {
+			result[i] = new FileEntry(all[i], this, fileModeStrategy);
+		}
+		return result;
+	}
+
 	/**
 	 * Checks whether the given hook is defined for the given repository, then
 	 * runs it with the given arguments.

org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java

@@ -47,11 +47,21 @@ package org.eclipse.jgit.util;
 import java.io.File;
 import java.io.IOException;
 import java.nio.charset.Charset;
+import java.nio.file.FileVisitOption;
+import java.nio.file.FileVisitResult;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.EnumSet;
 import java.util.List;
 
 import org.eclipse.jgit.errors.CommandFailedException;
+import org.eclipse.jgit.treewalk.FileTreeIterator.FileEntry;
+import org.eclipse.jgit.treewalk.FileTreeIterator.FileModeStrategy;
+import org.eclipse.jgit.treewalk.WorkingTreeIterator.Entry;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -119,6 +129,49 @@ public class FS_Win32 extends FS {
 		return true;
 	}
 
+	/** {@inheritDoc} */
+	@Override
+	public Entry[] list(File directory, FileModeStrategy fileModeStrategy) {
+		List<Entry> result = new ArrayList<>();
+		FS fs = this;
+		boolean checkExecutable = fs.supportsExecute();
+		try {
+			Files.walkFileTree(directory.toPath(),
+					EnumSet.noneOf(FileVisitOption.class), 1,
+					new SimpleFileVisitor<Path>() {
+						@Override
+						public FileVisitResult visitFile(Path file,
+								BasicFileAttributes attrs) throws IOException {
+							File f = file.toFile();
+							FS.Attributes attributes = new FS.Attributes(fs, f,
+									true, attrs.isDirectory(),
+									checkExecutable && f.canExecute(),
+									attrs.isSymbolicLink(),
+									attrs.isRegularFile(),
+									attrs.creationTime().toMillis(),
+									attrs.lastModifiedTime().toMillis(),
+									attrs.size());
+							result.add(new FileEntry(f, fs, attributes,
+									fileModeStrategy));
+							return FileVisitResult.CONTINUE;
+						}
+
+						@Override
+						public FileVisitResult visitFileFailed(Path file,
+								IOException exc) throws IOException {
+							// Just ignore it
+							return FileVisitResult.CONTINUE;
+						}
+					});
+		} catch (IOException e) {
+			// Ignore
+		}
+		if (result.isEmpty()) {
+			return NO_ENTRIES;
+		}
+		return result.toArray(new Entry[result.size()]);
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	protected File discoverGitExe() {