Add benchmark for strategies how to move a file

We can either
- try moving the file and, in case the target directory doesn't exist,
  handle the NoSuchFileException this raises to create the target
  directory
- or we always first test if the target directory exists and create it
 in case it is missing

On my Mac this yields

Benchmark                                        Mode  Cnt    Score     Error  Units
FileMoveBenchmark.moveFileToExistingDir        avgt    5  196.490 ±  15.194  us/op
FileMoveBenchmark.moveFileToExistingDirExists  avgt    5  223.217 ±  54.816  us/op
FileMoveBenchmark.moveFileToMissingDir         avgt    5  332.169 ±  43.871  us/op
FileMoveBenchmark.moveFileToMissingDirExists   avgt    5  303.815 ± 137.568  us/op

This means if the target directory of the move already exists the
first strategy is faster by around 25 us/op otherwise the second one
is faster by around 30 us/op. Which one is favorable depends on the
average probability that the target directory exists in real world
scenarios.

Change-Id: I03653b408b859a796508dfa1471b36c65633534e
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.benchmarks/src/org/eclipse/jgit/benchmarks/FileMoveBenchmark.java

@@ -0,0 +1,136 @@
+/*
+ * Copyright (C) 2020, Matthias Sohn <matthias.sohn@sap.com> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.benchmarks;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
+import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
+import java.util.concurrent.TimeUnit;
+
+import org.eclipse.jgit.util.FileUtils;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.TearDown;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.RunnerException;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+@State(Scope.Thread)
+public class FileMoveBenchmark {
+	int i;
+
+	Path testDir;
+
+	Path targetDir;
+
+	@Setup
+	public void setupBenchmark() throws IOException {
+		testDir = Files.createTempDirectory("dir");
+		targetDir = testDir.resolve("target");
+		Files.createDirectory(targetDir);
+	}
+
+	@TearDown
+	public void teardown() throws IOException {
+		FileUtils.delete(testDir.toFile(),
+				FileUtils.RECURSIVE | FileUtils.RETRY);
+	}
+
+	@Benchmark
+	@BenchmarkMode({ Mode.AverageTime })
+	@OutputTimeUnit(TimeUnit.MICROSECONDS)
+	@Warmup(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
+	@Measurement(iterations = 5, time = 5000, timeUnit = TimeUnit.MILLISECONDS)
+	public Path moveFileToExistingDir() throws IOException {
+		i++;
+		Path tmp = testDir.resolve("tmp" + i++);
+		Files.createFile(tmp);
+		Path targetDirectory = targetDir;
+		Path targetFile = targetDirectory.resolve("tmp" + i);
+		try {
+			return Files.move(tmp, targetFile, StandardCopyOption.ATOMIC_MOVE);
+		} catch (NoSuchFileException e) {
+			Files.createDirectory(targetDirectory);
+			return Files.move(tmp, targetFile, StandardCopyOption.ATOMIC_MOVE);
+		}
+	}
+
+	@Benchmark
+	@BenchmarkMode({ Mode.AverageTime })
+	@OutputTimeUnit(TimeUnit.MICROSECONDS)
+	@Warmup(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
+	@Measurement(iterations = 5, time = 5000, timeUnit = TimeUnit.MILLISECONDS)
+	public Path moveFileToExistingDirExists() throws IOException {
+		Path tmp = testDir.resolve("tmp" + i++);
+		Files.createFile(tmp);
+		Path targetDirectory = targetDir;
+		Path targetFile = targetDir.resolve("tmp" + i);
+		if (!targetDirectory.toFile().exists()) {
+			Files.createDirectory(targetDirectory);
+		}
+		return Files.move(tmp, targetFile, StandardCopyOption.ATOMIC_MOVE);
+	}
+
+	@Benchmark
+	@BenchmarkMode({ Mode.AverageTime })
+	@OutputTimeUnit(TimeUnit.MICROSECONDS)
+	@Warmup(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
+	@Measurement(iterations = 5, time = 5000, timeUnit = TimeUnit.MILLISECONDS)
+	public Path moveFileToMissingDir() throws IOException {
+		i++;
+		Path tmp = testDir.resolve("tmp" + i);
+		Files.createFile(tmp);
+		Path targetDirectory = testDir.resolve("target" + i);
+		Path targetFile = targetDirectory.resolve("tmp" + i);
+		try {
+			return Files.move(tmp, targetFile, StandardCopyOption.ATOMIC_MOVE);
+		} catch (NoSuchFileException e) {
+			Files.createDirectory(targetDirectory);
+			return Files.move(tmp, targetFile, StandardCopyOption.ATOMIC_MOVE);
+		}
+	}
+
+	@Benchmark
+	@BenchmarkMode({ Mode.AverageTime })
+	@OutputTimeUnit(TimeUnit.MICROSECONDS)
+	@Warmup(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
+	@Measurement(iterations = 5, time = 5000, timeUnit = TimeUnit.MILLISECONDS)
+	public Path moveFileToMissingDirExists() throws IOException {
+		i++;
+		Path tmp = testDir.resolve("tmp" + i);
+		Files.createFile(tmp);
+		Path targetDirectory = testDir.resolve("target" + i);
+		Path targetFile = targetDirectory.resolve("tmp" + i);
+		if (!targetDirectory.toFile().exists()) {
+			Files.createDirectory(targetDirectory);
+		}
+		return Files.move(tmp, targetFile, StandardCopyOption.ATOMIC_MOVE);
+	}
+
+	public static void main(String[] args) throws RunnerException {
+		Options opt = new OptionsBuilder()
+				.include(FileMoveBenchmark.class
+						.getSimpleName())
+				// .addProfiler(StackProfiler.class)
+				// .addProfiler(GCProfiler.class)
+				.forks(1).jvmArgs("-ea").build();
+		new Runner(opt).run();
+	}
+}