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>

4 files changed, 124 insertions, 16 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/FileTreeIterator.java b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/FileTreeIterator.java
index 0130cf97ec..06f53c2f3b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/FileTreeIterator.java
+++ b/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;
@@ -365,12 +382,12 @@ 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());
+			}
 		}
 
 		/**
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
index e6566939f8..cb68cee7bd 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
+++ b/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;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
index a2756e845c..27a437f4f5 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
+++ b/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;
@@ -82,6 +85,14 @@ 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)}.
 	 *
@@ -887,6 +898,29 @@ public abstract class FS {
 	}
 
 	/**
+	 * 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.
 	 * <p>
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java
index 29fe5dc829..a0ed04fe66 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java
+++ b/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;
 
@@ -121,6 +131,49 @@ public class FS_Win32 extends FS {
 
 	/** {@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() {
 		String path = SystemReader.getInstance().getenv("PATH"); //$NON-NLS-1$
 		File gitExe = searchPath(path, "git.exe", "git.cmd"); //$NON-NLS-1$ //$NON-NLS-2$