From 130aa312620cb016dbe8d7ad71bcf38512eb85fe Mon Sep 17 00:00:00 2001 From: Matthias Sohn Date: Fri, 12 Jul 2019 09:49:13 +0200 Subject: [PATCH] Add test for racy git detection in FileSnapshot Repeat the test 10000 times to get statistics if measured fsTimestampResolution is working in practice to detect racy git situations. Add a class to compute statistics for this test. Log delta between lastModified and time when FileSnapshot failed to detect modification. This happens if the racy git limit determined by measuring filesystem timestamp resolution and clock resolution is too small. If it would be correct FileSnapshot would always detect modification or mark it modified if time since modification is smaller than the racy git limit. Change-Id: Iabe7af1a7211ca58480f8902d4fa4e366932fc77 Signed-off-by: Matthias Sohn --- .../storage/file/FileSnapshotTest.java | 52 +++++++ .../tst/org/eclipse/jgit/util/StatsTest.java | 137 ++++++++++++++++++ org.eclipse.jgit/.settings/.api_filters | 8 + .../internal/storage/file/FileSnapshot.java | 23 ++- .../src/org/eclipse/jgit/util/Stats.java | 132 +++++++++++++++++ 5 files changed, 350 insertions(+), 2 deletions(-) create mode 100644 org.eclipse.jgit.test/tst/org/eclipse/jgit/util/StatsTest.java create mode 100644 org.eclipse.jgit/src/org/eclipse/jgit/util/Stats.java diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java index 1dea470848..9eb55db09c 100644 --- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java +++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java @@ -42,9 +42,13 @@ */ package org.eclipse.jgit.internal.storage.file; +import static org.eclipse.jgit.junit.JGitTestUtil.read; +import static org.eclipse.jgit.junit.JGitTestUtil.write; +import static org.junit.Assert.assertEquals; import static org.junit.Assert.assertFalse; import static org.junit.Assert.assertTrue; +import java.io.File; import java.io.IOException; import java.io.OutputStream; import java.nio.file.Files; @@ -54,17 +58,23 @@ import java.nio.file.StandardOpenOption; import java.nio.file.attribute.FileTime; import java.time.Duration; import java.time.Instant; +import java.util.ArrayList; import java.util.concurrent.TimeUnit; import org.eclipse.jgit.util.FS; import org.eclipse.jgit.util.FileUtils; +import org.eclipse.jgit.util.Stats; import org.eclipse.jgit.util.SystemReader; import org.junit.After; import org.junit.Assume; import org.junit.Before; import org.junit.Test; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; public class FileSnapshotTest { + private static final Logger LOG = LoggerFactory + .getLogger(FileSnapshotTest.class); private Path trash; @@ -205,6 +215,48 @@ public class FileSnapshotTest { assertTrue(fs2.equals(fs1)); } + @SuppressWarnings("boxing") + @Test + public void detectFileModified() throws IOException { + int failures = 0; + long racyNanos = 0; + final int COUNT = 10000; + ArrayList deltas = new ArrayList<>(); + File f = createFile("test").toFile(); + for (int i = 0; i < COUNT; i++) { + write(f, "a"); + FileSnapshot snapshot = FileSnapshot.save(f); + assertEquals("file should contain 'a'", "a", read(f)); + write(f, "b"); + if (!snapshot.isModified(f)) { + deltas.add(snapshot.lastDelta()); + racyNanos = snapshot.lastRacyNanos(); + failures++; + } + assertEquals("file should contain 'b'", "b", read(f)); + } + if (failures > 0) { + Stats stats = new Stats(); + LOG.debug( + "delta [ns] since modification FileSnapshot failed to detect"); + for (Long d : deltas) { + stats.add(d); + LOG.debug(String.format("%,d", d)); + } + LOG.error( + "count, failures, racy limit [ns], delta min [ns]," + + " delta max [ns], delta avg [ns]," + + " delta stddev [ns]"); + LOG.error(String.format( + "%,d, %,d, %,d, %,.0f, %,.0f, %,.0f, %,.0f", COUNT, + failures, racyNanos, stats.min(), stats.max(), + stats.avg(), stats.stddev())); + } + assertTrue( + "FileSnapshot: number of failures to detect file modifications should be 0", + failures == 0); + } + private Path createFile(String string) throws IOException { Files.createDirectories(trash); return Files.createTempFile(trash, string, "tdat"); diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/StatsTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/StatsTest.java new file mode 100644 index 0000000000..8b253828c4 --- /dev/null +++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/StatsTest.java @@ -0,0 +1,137 @@ +/* + * Copyright (C) 2019, Matthias Sohn + * 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.util; + +import static org.junit.Assert.assertEquals; +import static org.junit.Assert.assertTrue; + +import org.eclipse.jgit.util.Stats; +import org.junit.Test; + +public class StatsTest { + @Test + public void testStatsTrivial() { + Stats s = new Stats(); + s.add(1); + s.add(1); + s.add(1); + assertEquals(3, s.count()); + assertEquals(1.0, s.min(), 1E-6); + assertEquals(1.0, s.max(), 1E-6); + assertEquals(1.0, s.avg(), 1E-6); + assertEquals(0.0, s.var(), 1E-6); + assertEquals(0.0, s.stddev(), 1E-6); + } + + @Test + public void testStats() { + Stats s = new Stats(); + s.add(1); + s.add(2); + s.add(3); + s.add(4); + assertEquals(4, s.count()); + assertEquals(1.0, s.min(), 1E-6); + assertEquals(4.0, s.max(), 1E-6); + assertEquals(2.5, s.avg(), 1E-6); + assertEquals(1.666667, s.var(), 1E-6); + assertEquals(1.290994, s.stddev(), 1E-6); + } + + @Test + /** + * see + * https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Example + */ + public void testStatsCancellationExample1() { + Stats s = new Stats(); + s.add(1E8 + 4); + s.add(1E8 + 7); + s.add(1E8 + 13); + s.add(1E8 + 16); + assertEquals(4, s.count()); + assertEquals(1E8 + 4, s.min(), 1E-6); + assertEquals(1E8 + 16, s.max(), 1E-6); + assertEquals(1E8 + 10, s.avg(), 1E-6); + assertEquals(30, s.var(), 1E-6); + assertEquals(5.477226, s.stddev(), 1E-6); + } + + @Test + /** + * see + * https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Example + */ + public void testStatsCancellationExample2() { + Stats s = new Stats(); + s.add(1E9 + 4); + s.add(1E9 + 7); + s.add(1E9 + 13); + s.add(1E9 + 16); + assertEquals(4, s.count()); + assertEquals(1E9 + 4, s.min(), 1E-6); + assertEquals(1E9 + 16, s.max(), 1E-6); + assertEquals(1E9 + 10, s.avg(), 1E-6); + assertEquals(30, s.var(), 1E-6); + assertEquals(5.477226, s.stddev(), 1E-6); + } + + @Test + public void testNoValues() { + Stats s = new Stats(); + assertTrue(Double.isNaN(s.var())); + assertTrue(Double.isNaN(s.stddev())); + assertTrue(Double.isNaN(s.avg())); + assertTrue(Double.isNaN(s.min())); + assertTrue(Double.isNaN(s.max())); + s.add(42.3); + assertTrue(Double.isNaN(s.var())); + assertTrue(Double.isNaN(s.stddev())); + assertEquals(42.3, s.avg(), 1E-6); + assertEquals(42.3, s.max(), 1E-6); + assertEquals(42.3, s.min(), 1E-6); + s.add(42.3); + assertEquals(0, s.var(), 1E-6); + assertEquals(0, s.stddev(), 1E-6); + } +} diff --git a/org.eclipse.jgit/.settings/.api_filters b/org.eclipse.jgit/.settings/.api_filters index 01215a8c70..59bafc52e0 100644 --- a/org.eclipse.jgit/.settings/.api_filters +++ b/org.eclipse.jgit/.settings/.api_filters @@ -226,4 +226,12 @@ + + + + + + + + diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java index ec71783c6e..2a490a4a1f 100644 --- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java +++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java @@ -283,6 +283,10 @@ public class FileSnapshot { private boolean wasRacyClean; + private long delta; + + private long racyNanos; + private FileSnapshot(Instant read, Instant modified, long size, @NonNull Duration fsTimestampResolution, @NonNull Object fileKey) { this.file = null; @@ -466,6 +470,21 @@ public class FileSnapshot { return wasRacyClean; } + /** + * @return the delta in nanoseconds between lastModified and lastRead during + * last racy check + */ + long lastDelta() { + return delta; + } + + /** + * @return the racyNanos threshold in nanoseconds during last racy check + */ + long lastRacyNanos() { + return racyNanos; + } + /** {@inheritDoc} */ @SuppressWarnings("nls") @Override @@ -483,8 +502,8 @@ public class FileSnapshot { private boolean isRacyClean(Instant read) { // add a 10% safety margin - long racyNanos = (fsTimestampResolution.toNanos() + 1) * 11 / 10; - long delta = Duration.between(lastModified, read).toNanos(); + racyNanos = (fsTimestampResolution.toNanos() + 1) * 11 / 10; + delta = Duration.between(lastModified, read).toNanos(); wasRacyClean = delta <= racyNanos; if (LOG.isDebugEnabled()) { LOG.debug( diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/Stats.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/Stats.java new file mode 100644 index 0000000000..e9307d342b --- /dev/null +++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/Stats.java @@ -0,0 +1,132 @@ +/* + * Copyright (C) 2019, Matthias Sohn + * 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.util; + +/** + * Simple double statistics, computed incrementally, variance and standard + * deviation using Welford's online algorithm, see + * https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Welford's_online_algorithm + * + * @since 5.1.9 + */ +public class Stats { + private int n = 0; + + private double avg = 0.0; + + private double min = 0.0; + + private double max = 0.0; + + private double sum = 0.0; + + /** + * Add a value + * + * @param x + * value + */ + public void add(double x) { + n++; + min = n == 1 ? x : Math.min(min, x); + max = n == 1 ? x : Math.max(max, x); + double d = x - avg; + avg += d / n; + sum += d * d * (n - 1) / n; + } + + /** + * @return number of the added values + */ + public int count() { + return n; + } + + /** + * @return minimum of the added values + */ + public double min() { + if (n < 1) { + return Double.NaN; + } + return min; + } + + /** + * @return maximum of the added values + */ + public double max() { + if (n < 1) { + return Double.NaN; + } + return max; + } + + /** + * @return average of the added values + */ + + public double avg() { + if (n < 1) { + return Double.NaN; + } + return avg; + } + + /** + * @return variance of the added values + */ + public double var() { + if (n < 2) { + return Double.NaN; + } + return sum / (n - 1); + } + + /** + * @return standard deviation of the added values + */ + public double stddev() { + return Math.sqrt(this.var()); + } +} -- 2.39.5