com.google.gerrit.server.notedb.RepoSequence Maven / Gradle / Ivy
// Copyright (C) 2016 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.notedb;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.gerrit.entities.RefNames.REFS;
import static com.google.gerrit.entities.RefNames.REFS_SEQUENCES;
import static java.nio.charset.StandardCharsets.UTF_8;
import static java.util.Objects.requireNonNull;
import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
import com.github.rholder.retry.RetryException;
import com.github.rholder.retry.Retryer;
import com.github.rholder.retry.RetryerBuilder;
import com.github.rholder.retry.StopStrategies;
import com.github.rholder.retry.WaitStrategies;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.flogger.FluentLogger;
import com.google.common.util.concurrent.Runnables;
import com.google.gerrit.entities.Project;
import com.google.gerrit.entities.RefNames;
import com.google.gerrit.exceptions.StorageException;
import com.google.gerrit.git.LockFailureException;
import com.google.gerrit.git.RefUpdateUtil;
import com.google.gerrit.server.extensions.events.GitReferenceUpdated;
import com.google.gerrit.server.git.GitRepositoryManager;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.RefUpdate;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.transport.ReceiveCommand;
/**
* Class for managing an incrementing sequence backed by a git repository.
*
* The current sequence number is stored as UTF-8 text in a blob pointed to by a ref in the
* {@code refs/sequences/*} namespace. Multiple processes can share the same sequence by
* incrementing the counter using normal git ref updates. To amortize the cost of these ref updates,
* processes can increment the counter by a larger number and hand out numbers from that range in
* memory until they run out. This means concurrent processes will hand out somewhat non-monotonic
* numbers.
*/
public class RepoSequence {
private static final FluentLogger logger = FluentLogger.forEnclosingClass();
@FunctionalInterface
public interface Seed {
int get();
}
@VisibleForTesting
static RetryerBuilder> retryerBuilder() {
return RetryerBuilder.>newBuilder()
.retryIfException(
t ->
t instanceof StorageException
&& ((StorageException) t).getCause() instanceof LockFailureException)
.withWaitStrategy(
WaitStrategies.join(
WaitStrategies.exponentialWait(5, TimeUnit.SECONDS),
WaitStrategies.randomWait(50, TimeUnit.MILLISECONDS)))
.withStopStrategy(StopStrategies.stopAfterDelay(30, TimeUnit.SECONDS));
}
private static final Retryer> RETRYER = retryerBuilder().build();
private final GitRepositoryManager repoManager;
private final GitReferenceUpdated gitRefUpdated;
private final Project.NameKey projectName;
private final String refName;
private final Seed seed;
private final int floor;
private final int batchSize;
private final Runnable afterReadRef;
private final Retryer> retryer;
// Protects all non-final fields.
private final Lock counterLock;
private int limit;
private int counter;
@VisibleForTesting int acquireCount;
public RepoSequence(
GitRepositoryManager repoManager,
GitReferenceUpdated gitRefUpdated,
Project.NameKey projectName,
String name,
Seed seed,
int batchSize) {
this(
repoManager,
gitRefUpdated,
projectName,
name,
seed,
batchSize,
Runnables.doNothing(),
RETRYER,
0);
}
public RepoSequence(
GitRepositoryManager repoManager,
GitReferenceUpdated gitRefUpdated,
Project.NameKey projectName,
String name,
Seed seed,
int batchSize,
int floor) {
this(
repoManager,
gitRefUpdated,
projectName,
name,
seed,
batchSize,
Runnables.doNothing(),
RETRYER,
floor);
}
@VisibleForTesting
RepoSequence(
GitRepositoryManager repoManager,
GitReferenceUpdated gitRefUpdated,
Project.NameKey projectName,
String name,
Seed seed,
int batchSize,
Runnable afterReadRef,
Retryer> retryer) {
this(repoManager, gitRefUpdated, projectName, name, seed, batchSize, afterReadRef, retryer, 0);
}
RepoSequence(
GitRepositoryManager repoManager,
GitReferenceUpdated gitRefUpdated,
Project.NameKey projectName,
String name,
Seed seed,
int batchSize,
Runnable afterReadRef,
Retryer> retryer,
int floor) {
this.repoManager = requireNonNull(repoManager, "repoManager");
this.gitRefUpdated = requireNonNull(gitRefUpdated, "gitRefUpdated");
this.projectName = requireNonNull(projectName, "projectName");
checkArgument(
name != null
&& !name.startsWith(REFS)
&& !name.startsWith(REFS_SEQUENCES.substring(REFS.length())),
"name should be a suffix to follow \"refs/sequences/\", got: %s",
name);
this.refName = RefNames.REFS_SEQUENCES + name;
this.seed = requireNonNull(seed, "seed");
this.floor = floor;
checkArgument(batchSize > 0, "expected batchSize > 0, got: %s", batchSize);
this.batchSize = batchSize;
this.afterReadRef = requireNonNull(afterReadRef, "afterReadRef");
this.retryer = requireNonNull(retryer, "retryer");
logger.atFine().log("sequence batch size for %s is %s", name, batchSize);
counterLock = new ReentrantLock(true);
}
/**
* Retrieves the next available sequence number.
*
* This method is thread-safe.
*
* @return the next available sequence number
*/
public int next() {
return Iterables.getOnlyElement(next(1));
}
/**
* Retrieves the next N available sequence number.
*
*
This method is thread-safe.
*
* @param count the number of sequence numbers which should be returned
* @return the next N available sequence numbers
*/
public ImmutableList next(int count) {
if (count == 0) {
return ImmutableList.of();
}
checkArgument(count > 0, "count is negative: %s", count);
try {
return retryer.call(
() -> {
counterLock.lock();
try {
if (count == 1) {
if (counter >= limit) {
acquire(batchSize);
}
return ImmutableList.of(counter++);
}
List ids = new ArrayList<>(count);
while (counter < limit) {
ids.add(counter++);
if (ids.size() == count) {
return ImmutableList.copyOf(ids);
}
}
acquire(Math.max(count - ids.size(), batchSize));
while (ids.size() < count) {
ids.add(counter++);
}
return ImmutableList.copyOf(ids);
} finally {
counterLock.unlock();
}
});
} catch (ExecutionException | RetryException e) {
if (e.getCause() != null) {
Throwables.throwIfInstanceOf(e.getCause(), StorageException.class);
}
throw new StorageException(e);
}
}
/**
* Updates the next available sequence number in NoteDb in order to have a batch of sequence
* numbers available that can be handed out. {@link #counter} stores the next sequence number that
* can be handed out. When {@link #limit} is reached a new batch of sequence numbers needs to be
* retrieved by calling this method.
*
* Note: Callers are required to acquire the {@link #counterLock} before
* calling this method.
*
* @param count the number of sequence numbers which should be retrieved
*/
private void acquire(int count) {
try (Repository repo = repoManager.openRepository(projectName);
RevWalk rw = new RevWalk(repo)) {
logger.atFine().log("acquire %d ids on %s in %s", count, refName, projectName);
Optional blob = IntBlob.parse(repo, refName, rw);
afterReadRef.run();
ObjectId oldId;
int next;
if (!blob.isPresent()) {
oldId = ObjectId.zeroId();
next = seed.get();
} else {
oldId = blob.get().id();
next = blob.get().value();
}
next = Math.max(floor, next);
RefUpdate refUpdate =
IntBlob.tryStore(repo, rw, projectName, refName, oldId, next + count, gitRefUpdated);
RefUpdateUtil.checkResult(refUpdate);
counter = next;
limit = counter + count;
acquireCount++;
} catch (IOException e) {
throw new StorageException(e);
}
}
public static ReceiveCommand storeNew(ObjectInserter ins, String name, int val)
throws IOException {
ObjectId newId = ins.insert(OBJ_BLOB, Integer.toString(val).getBytes(UTF_8));
return new ReceiveCommand(ObjectId.zeroId(), newId, RefNames.REFS_SEQUENCES + name);
}
public void storeNew(int value) {
counterLock.lock();
try (Repository repo = repoManager.openRepository(projectName);
RevWalk rw = new RevWalk(repo)) {
Optional blob = IntBlob.parse(repo, refName, rw);
afterReadRef.run();
ObjectId oldId;
if (!blob.isPresent()) {
oldId = ObjectId.zeroId();
} else {
oldId = blob.get().id();
}
RefUpdate refUpdate =
IntBlob.tryStore(repo, rw, projectName, refName, oldId, value, gitRefUpdated);
RefUpdateUtil.checkResult(refUpdate);
counter = value;
limit = counter + batchSize;
acquireCount++;
} catch (IOException e) {
throw new StorageException(e);
} finally {
counterLock.unlock();
}
}
public int current() {
counterLock.lock();
try (Repository repo = repoManager.openRepository(projectName);
RevWalk rw = new RevWalk(repo)) {
Optional blob = IntBlob.parse(repo, refName, rw);
int current;
if (!blob.isPresent()) {
current = seed.get();
} else {
current = blob.get().value();
}
return current;
} catch (IOException e) {
throw new StorageException(e);
} finally {
counterLock.unlock();
}
}
/**
* Retrieves the last returned sequence number.
*
* Explicitly calls {@link #next()} if this instance didn't return sequence number until now.
*/
public int last() {
if (counter == 0) {
next();
}
return counter - 1;
}
}