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// Copyright (C) 2020 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.gerrit.server.patch.gitfilediff;
import static java.util.function.Function.identity;
import com.google.auto.value.AutoValue;
import com.google.common.base.Throwables;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.MultimapBuilder;
import com.google.common.collect.Multimaps;
import com.google.common.collect.Streams;
import com.google.gerrit.entities.Patch;
import com.google.gerrit.entities.Project;
import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
import com.google.gerrit.metrics.Counter0;
import com.google.gerrit.metrics.Description;
import com.google.gerrit.metrics.MetricMaker;
import com.google.gerrit.server.cache.CacheModule;
import com.google.gerrit.server.config.ConfigUtil;
import com.google.gerrit.server.config.GerritServerConfig;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.logging.Metadata;
import com.google.gerrit.server.logging.TraceContext;
import com.google.gerrit.server.logging.TraceContext.TraceTimer;
import com.google.gerrit.server.patch.DiffExecutor;
import com.google.gerrit.server.patch.DiffNotAvailableException;
import com.google.gerrit.server.util.git.CloseablePool;
import com.google.inject.Inject;
import com.google.inject.Module;
import com.google.inject.Singleton;
import com.google.inject.name.Named;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.stream.Collectors;
import org.eclipse.jgit.diff.DiffEntry;
import org.eclipse.jgit.diff.DiffEntry.ChangeType;
import org.eclipse.jgit.diff.DiffFormatter;
import org.eclipse.jgit.diff.HistogramDiff;
import org.eclipse.jgit.diff.RawTextComparator;
import org.eclipse.jgit.lib.AbbreviatedObjectId;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.patch.FileHeader;
import org.eclipse.jgit.util.io.DisabledOutputStream;
/** Implementation of the {@link GitFileDiffCache} */
@Singleton
public class GitFileDiffCacheImpl implements GitFileDiffCache {
private static final String GIT_DIFF = "git_file_diff";
public static Module module() {
return new CacheModule() {
@Override
protected void configure() {
bind(GitFileDiffCache.class).to(GitFileDiffCacheImpl.class);
persist(GIT_DIFF, GitFileDiffCacheKey.class, GitFileDiff.class)
.maximumWeight(10 << 20)
.weigher(GitFileDiffWeigher.class)
.keySerializer(GitFileDiffCacheKey.Serializer.INSTANCE)
.valueSerializer(GitFileDiff.Serializer.INSTANCE)
.version(3)
.loader(GitFileDiffCacheImpl.Loader.class);
}
};
}
@Singleton
static class Metrics {
final Counter0 timeouts;
@Inject
Metrics(MetricMaker metricMaker) {
timeouts =
metricMaker.newCounter(
"caches/diff/timeouts",
new Description(
"Total number of git file diff computations that resulted in timeouts.")
.setRate()
.setUnit("count"));
}
}
/** Enum for the supported diff algorithms for the file diff computation. */
public enum DiffAlgorithm {
HISTOGRAM_WITH_FALLBACK_MYERS,
HISTOGRAM_NO_FALLBACK
}
/** Creates a new JGit diff algorithm instance using the Gerrit's {@link DiffAlgorithm} enum. */
public static class DiffAlgorithmFactory {
public static org.eclipse.jgit.diff.DiffAlgorithm create(DiffAlgorithm diffAlgorithm) {
HistogramDiff result = new HistogramDiff();
if (diffAlgorithm.equals(DiffAlgorithm.HISTOGRAM_NO_FALLBACK)) {
result.setFallbackAlgorithm(null);
}
return result;
}
}
private final LoadingCache cache;
@Inject
public GitFileDiffCacheImpl(
@Named(GIT_DIFF) LoadingCache cache) {
this.cache = cache;
}
@Override
public GitFileDiff get(GitFileDiffCacheKey key) throws DiffNotAvailableException {
try {
return cache.get(key);
} catch (ExecutionException e) {
throw new DiffNotAvailableException(e);
}
}
@Override
public ImmutableMap getAll(Iterable keys)
throws DiffNotAvailableException {
try {
return cache.getAll(keys);
} catch (ExecutionException e) {
throw new DiffNotAvailableException(e);
}
}
static class Loader extends CacheLoader {
private final GitRepositoryManager repoManager;
private final ExecutorService diffExecutor;
private final long timeoutMillis;
private final Metrics metrics;
@Inject
public Loader(
@GerritServerConfig Config cfg,
GitRepositoryManager repoManager,
@DiffExecutor ExecutorService de,
Metrics metrics) {
this.repoManager = repoManager;
this.diffExecutor = de;
this.timeoutMillis =
ConfigUtil.getTimeUnit(
cfg,
"cache",
GIT_DIFF,
"timeout",
TimeUnit.MILLISECONDS.convert(5, TimeUnit.SECONDS),
TimeUnit.MILLISECONDS);
this.metrics = metrics;
}
@Override
public GitFileDiff load(GitFileDiffCacheKey key) throws IOException, DiffNotAvailableException {
try (TraceTimer timer =
TraceContext.newTimer(
"Loading a single key from git file diff cache",
Metadata.builder()
.diffAlgorithm(key.diffAlgorithm().name())
.filePath(key.newFilePath())
.build())) {
return loadAll(ImmutableList.of(key)).get(key);
}
}
@Override
public Map loadAll(
Iterable keys)
throws IOException, DiffNotAvailableException {
try (TraceTimer timer =
TraceContext.newTimer("Loading multiple keys from git file diff cache")) {
ImmutableMap.Builder result =
ImmutableMap.builderWithExpectedSize(Iterables.size(keys));
Map> byProject =
Streams.stream(keys)
.distinct()
.collect(Collectors.groupingBy(GitFileDiffCacheKey::project));
for (Map.Entry> entry : byProject.entrySet()) {
try (Repository repo = repoManager.openRepository(entry.getKey())) {
// Grouping keys by diff options because each group of keys will be processed with a
// separate call to JGit using the DiffFormatter object.
Map> optionsGroups =
entry.getValue().stream().collect(Collectors.groupingBy(DiffOptions::fromKey));
for (Map.Entry> group :
optionsGroups.entrySet()) {
result.putAll(loadAllImpl(repo, group.getKey(), group.getValue()));
}
}
}
return result.build();
}
}
/**
* Loads the git file diffs for all keys of the same repository, and having the same diff {@code
* options}.
*
* @return The git file diffs for all input keys.
*/
private Map loadAllImpl(
Repository repo, DiffOptions options, List keys)
throws IOException, DiffNotAvailableException {
ImmutableMap.Builder result =
ImmutableMap.builderWithExpectedSize(keys.size());
Map filePaths =
keys.stream().collect(Collectors.toMap(identity(), GitFileDiffCacheKey::newFilePath));
try (CloseablePool diffPool =
new CloseablePool<>(() -> createDiffFormatter(options, repo))) {
ListMultimap diffEntries;
try (CloseablePool.Handle formatter = diffPool.get()) {
diffEntries = loadDiffEntries(formatter.get(), options, filePaths.values());
}
for (GitFileDiffCacheKey key : filePaths.keySet()) {
String newFilePath = filePaths.get(key);
if (!diffEntries.containsKey(newFilePath)) {
result.put(
key,
GitFileDiff.empty(
AbbreviatedObjectId.fromObjectId(key.oldTree()),
AbbreviatedObjectId.fromObjectId(key.newTree()),
newFilePath));
continue;
}
List entries = diffEntries.get(newFilePath);
if (entries.size() == 1) {
result.put(key, createGitFileDiff(entries.get(0), key, diffPool));
} else {
// Handle when JGit returns two {Added, Deleted} entries for the same file. This
// happens, for example, when a file's mode is changed between patchsets (e.g.
// converting a symlink to a regular file). We combine both diff entries into a single
// entry with {changeType = Rewrite}.
List gitDiffs = new ArrayList<>();
for (DiffEntry entry : diffEntries.get(newFilePath)) {
gitDiffs.add(createGitFileDiff(entry, key, diffPool));
}
result.put(key, createRewriteEntry(gitDiffs));
}
}
return result.build();
}
}
private static ListMultimap loadDiffEntries(
DiffFormatter diffFormatter, DiffOptions diffOptions, Collection filePaths)
throws IOException {
Set filePathsSet = ImmutableSet.copyOf(filePaths);
List diffEntries =
diffFormatter.scan(
diffOptions.oldTree().equals(ObjectId.zeroId()) ? null : diffOptions.oldTree(),
diffOptions.newTree());
return diffEntries.stream()
.filter(d -> filePathsSet.contains(extractPath(d)))
.collect(
Multimaps.toMultimap(
Loader::extractPath,
identity(),
MultimapBuilder.treeKeys().arrayListValues()::build));
}
private static DiffFormatter createDiffFormatter(DiffOptions diffOptions, Repository repo) {
try (DiffFormatter diffFormatter = new DiffFormatter(DisabledOutputStream.INSTANCE)) {
diffFormatter.setRepository(repo);
RawTextComparator cmp = comparatorFor(diffOptions.whitespace());
diffFormatter.setDiffComparator(cmp);
if (diffOptions.renameScore() != -1) {
diffFormatter.setDetectRenames(true);
diffFormatter.getRenameDetector().setRenameScore(diffOptions.renameScore());
}
diffFormatter.setDiffAlgorithm(DiffAlgorithmFactory.create(diffOptions.diffAlgorithm()));
diffFormatter.getRenameDetector().setSkipContentRenamesForBinaryFiles(true);
return diffFormatter;
}
}
private static RawTextComparator comparatorFor(Whitespace ws) {
switch (ws) {
case IGNORE_ALL:
return RawTextComparator.WS_IGNORE_ALL;
case IGNORE_TRAILING:
return RawTextComparator.WS_IGNORE_TRAILING;
case IGNORE_LEADING_AND_TRAILING:
return RawTextComparator.WS_IGNORE_CHANGE;
case IGNORE_NONE:
default:
return RawTextComparator.DEFAULT;
}
}
/**
* Create a {@link GitFileDiff}. The result depends on the value of the {@code useTimeout} field
* of the {@code key} parameter.
*
*
*
If {@code useTimeout} is true, the computation is performed with timeout enforcement
* (identified by {@link #timeoutMillis}). If the timeout is exceeded, this method returns
* a negative result using {@link GitFileDiff#createNegative(AbbreviatedObjectId,
* AbbreviatedObjectId, String)}.
*
If {@code useTimeouts} is false, the computation is performed synchronously without
* timeout enforcement.
*/
private GitFileDiff createGitFileDiff(
DiffEntry diffEntry, GitFileDiffCacheKey key, CloseablePool diffPool)
throws IOException {
if (!key.useTimeout()) {
try (CloseablePool.Handle formatter = diffPool.get()) {
FileHeader fileHeader = formatter.get().toFileHeader(diffEntry);
return GitFileDiff.create(diffEntry, fileHeader);
}
}
// This submits the DiffFormatter to a different thread. The CloseablePool and our usage of it
// ensures that any DiffFormatter instance and the ObjectReader it references internally is
// only used by a single thread concurrently. However, ObjectReaders have a reference to
// Repository which might not be thread safe (FileRepository is, DfsRepository might not).
// This could lead to a race condition.
Future fileDiffFuture =
diffExecutor.submit(
() -> {
try (CloseablePool.Handle formatter = diffPool.get()) {
return GitFileDiff.create(diffEntry, formatter.get().toFileHeader(diffEntry));
}
});
try {
// We employ the timeout because of a bug in Myers diff in JGit. See
// bugs.chromium.org/p/gerrit/issues/detail?id=487 for more details. The bug may happen
// if the algorithm used in diffs is HISTOGRAM_WITH_FALLBACK_MYERS.
return fileDiffFuture.get(timeoutMillis, TimeUnit.MILLISECONDS);
} catch (InterruptedException | TimeoutException e) {
// If timeout happens, create a negative result
metrics.timeouts.increment();
return GitFileDiff.createNegative(
AbbreviatedObjectId.fromObjectId(key.oldTree()),
AbbreviatedObjectId.fromObjectId(key.newTree()),
key.newFilePath());
} catch (ExecutionException e) {
// If there was an error computing the result, carry it
// up to the caller so the cache knows this key is invalid.
Throwables.throwIfInstanceOf(e.getCause(), IOException.class);
throw new IOException(e.getMessage(), e.getCause());
}
}
/**
* Extract the file path from a {@link DiffEntry}. Returns the old file path if the entry
* corresponds to a deleted file, otherwise it returns the new file path.
*/
private static String extractPath(DiffEntry diffEntry) {
return diffEntry.getChangeType().equals(ChangeType.DELETE)
? diffEntry.getOldPath()
: diffEntry.getNewPath();
}
}
/**
* Create a single {@link GitFileDiff} with {@link com.google.gerrit.entities.Patch.ChangeType}
* equals {@link com.google.gerrit.entities.Patch.ChangeType#REWRITE}, assuming the input list
* contains two entries.
*
* @param gitDiffs input list of exactly two {@link GitFileDiff} for same file path.
* @return a single {@link GitFileDiff} with change type equals {@link
* com.google.gerrit.entities.Patch.ChangeType#REWRITE}.
* @throws DiffNotAvailableException if input list contains git diffs with change types other than
* {ADDED, DELETED}. This is a JGit error.
*/
private static GitFileDiff createRewriteEntry(List gitDiffs)
throws DiffNotAvailableException {
if (gitDiffs.size() != 2) {
throw new DiffNotAvailableException(
String.format(
"JGit error: found %d dff entries for same file path %s",
gitDiffs.size(), gitDiffs.get(0).getDefaultPath()));
}
// Convert the first entry (prioritized according to change type enum order) to REWRITE
gitDiffs.sort(Comparator.comparingInt(o -> o.changeType().ordinal()));
return gitDiffs.get(0).toBuilder().changeType(Patch.ChangeType.REWRITE).build();
}
/** An entity representing the options affecting the diff computation. */
@AutoValue
abstract static class DiffOptions {
/** Convert a {@link GitFileDiffCacheKey} input to a {@link DiffOptions}. */
static DiffOptions fromKey(GitFileDiffCacheKey key) {
return create(
key.oldTree(), key.newTree(), key.renameScore(), key.whitespace(), key.diffAlgorithm());
}
private static DiffOptions create(
ObjectId oldTree,
ObjectId newTree,
Integer renameScore,
Whitespace whitespace,
DiffAlgorithm diffAlgorithm) {
return new AutoValue_GitFileDiffCacheImpl_DiffOptions(
oldTree, newTree, renameScore, whitespace, diffAlgorithm);
}
abstract ObjectId oldTree();
abstract ObjectId newTree();
abstract Integer renameScore();
abstract Whitespace whitespace();
abstract DiffAlgorithm diffAlgorithm();
}
}
