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Highly-available version-controlled service configuration repository based on Git, ZooKeeper and HTTP/2 (centraldogma-client)
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/*
* Copyright 2018 LINE Corporation
*
* LINE Corporation licenses this file to you 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:
*
* https://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.linecorp.centraldogma.client;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.math.LongMath.saturatedAdd;
import static java.util.Objects.requireNonNull;
import java.util.AbstractMap.SimpleImmutableEntry;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionException;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.Executor;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BiConsumer;
import javax.annotation.Nullable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.google.common.base.MoreObjects;
import com.linecorp.centraldogma.common.CentralDogmaException;
import com.linecorp.centraldogma.common.EntryNotFoundException;
import com.linecorp.centraldogma.common.PathPattern;
import com.linecorp.centraldogma.common.Query;
import com.linecorp.centraldogma.common.RepositoryNotFoundException;
import com.linecorp.centraldogma.common.Revision;
abstract class AbstractWatcher implements Watcher {
private static final Logger logger = LoggerFactory.getLogger(AbstractWatcher.class);
private enum State {
INIT,
STARTED,
STOPPED
}
private final ScheduledExecutorService watchScheduler;
private final String projectName;
private final String repositoryName;
private final String pathPattern;
private final boolean errorOnEntryNotFound;
private final long delayOnSuccessMillis;
private final long initialDelayMillis;
private final long maxDelayMillis;
private final double multiplier;
private final double jitterRate;
private final List, Executor>> updateListeners =
new CopyOnWriteArrayList<>();
private final AtomicReference state = new AtomicReference<>(State.INIT);
private final CompletableFuture> initialValueFuture = new CompletableFuture<>();
@Nullable
private volatile Latest latest;
@Nullable
private volatile ScheduledFuture currentScheduleFuture;
@Nullable
private volatile CompletableFuture currentWatchFuture;
AbstractWatcher(ScheduledExecutorService watchScheduler, String projectName, String repositoryName,
String pathPattern, boolean errorOnEntryNotFound, long delayOnSuccessMillis,
long initialDelayMillis, long maxDelayMillis, double multiplier, double jitterRate) {
this.watchScheduler = watchScheduler;
this.projectName = projectName;
this.repositoryName = repositoryName;
this.pathPattern = pathPattern;
this.errorOnEntryNotFound = errorOnEntryNotFound;
this.delayOnSuccessMillis = delayOnSuccessMillis;
this.initialDelayMillis = initialDelayMillis;
this.maxDelayMillis = maxDelayMillis;
this.multiplier = multiplier;
this.jitterRate = jitterRate;
}
@Override
public ScheduledExecutorService watchScheduler() {
return watchScheduler;
}
@Override
public CompletableFuture> initialValueFuture() {
return initialValueFuture;
}
@Override
public Latest latest() {
final Latest latest = this.latest;
if (latest == null) {
throw new IllegalStateException("value not available yet");
}
return latest;
}
/**
* Starts to watch the file specified in the {@link Query} or the {@link PathPattern}
* given with the constructor.
*/
void start() {
if (state.compareAndSet(State.INIT, State.STARTED)) {
scheduleWatch(0);
}
}
@Override
public void close() {
state.set(State.STOPPED);
if (!initialValueFuture.isDone()) {
initialValueFuture.cancel(false);
}
// Cancel any scheduled operations.
final ScheduledFuture currentScheduleFuture = this.currentScheduleFuture;
if (currentScheduleFuture != null && !currentScheduleFuture.isDone()) {
currentScheduleFuture.cancel(false);
}
final CompletableFuture currentWatchFuture = this.currentWatchFuture;
if (currentWatchFuture != null && !currentWatchFuture.isDone()) {
currentWatchFuture.cancel(false);
}
}
private boolean isStopped() {
return state.get() == State.STOPPED;
}
@Override
public void watch(BiConsumer listener) {
watch(listener, watchScheduler);
}
@Override
public void watch(BiConsumer listener, Executor executor) {
requireNonNull(listener, "listener");
checkState(!isStopped(), "watcher closed");
updateListeners.add(new SimpleImmutableEntry<>(listener, executor));
final Latest latest = this.latest;
if (latest != null) {
// There's a chance that listener.accept(...) is called twice for the same value
// if this watch method is called:
// - after " this.latest = newLatest;" is invoked.
// - and before notifyListener() is called.
// However, it's such a rare case and we usually call `watch` method right after creating a Watcher,
// which means latest is probably not set yet, so we don't use a lock to guarantee
// the atomicity.
executor.execute(() -> listener.accept(latest.revision(), latest.value()));
}
}
private void scheduleWatch(int numAttemptsSoFar) {
if (isStopped()) {
return;
}
final long delay;
if (numAttemptsSoFar == 0) {
delay = latest != null ? delayOnSuccessMillis : 0;
} else {
delay = nextDelayMillis(numAttemptsSoFar);
}
currentScheduleFuture = watchScheduler.schedule(() -> {
currentScheduleFuture = null;
doWatch(numAttemptsSoFar);
}, delay, TimeUnit.MILLISECONDS);
}
private long nextDelayMillis(int numAttemptsSoFar) {
final long nextDelayMillis;
if (numAttemptsSoFar == 1) {
nextDelayMillis = initialDelayMillis;
} else {
nextDelayMillis =
Math.min(saturatedMultiply(initialDelayMillis, Math.pow(multiplier, numAttemptsSoFar - 1)),
maxDelayMillis);
}
final long minJitter = (long) (nextDelayMillis * (1 - jitterRate));
final long maxJitter = (long) (nextDelayMillis * (1 + jitterRate));
final long bound = maxJitter - minJitter + 1;
final long millis = random(bound);
return Math.max(0, saturatedAdd(minJitter, millis));
}
private static long saturatedMultiply(long left, double right) {
final double result = left * right;
return result >= Long.MAX_VALUE ? Long.MAX_VALUE : (long) result;
}
private static long random(long bound) {
assert bound > 0;
final long mask = bound - 1;
final Random random = ThreadLocalRandom.current();
long result = random.nextLong();
if ((bound & mask) == 0L) {
// power of two
result &= mask;
} else { // reject over-represented candidates
for (long u = result >>> 1; u + mask - (result = u % bound) < 0L; u = random.nextLong() >>> 1) {
continue;
}
}
return result;
}
private void doWatch(int numAttemptsSoFar) {
if (isStopped()) {
return;
}
final Latest latest = this.latest;
final Revision lastKnownRevision = latest != null ? latest.revision() : Revision.INIT;
final CompletableFuture> f = doWatch(lastKnownRevision);
currentWatchFuture = f;
f.thenAccept(newLatest -> {
currentWatchFuture = null;
if (newLatest != null) {
this.latest = newLatest;
logger.debug("watcher noticed updated file {}/{}{}: rev={}",
projectName, repositoryName, pathPattern, newLatest.revision());
notifyListeners(newLatest);
if (!initialValueFuture.isDone()) {
initialValueFuture.complete(newLatest);
}
}
// Watch again for the next change.
scheduleWatch(0);
})
.exceptionally(thrown -> {
currentWatchFuture = null;
try {
final Throwable cause = thrown instanceof CompletionException ? thrown.getCause() : thrown;
boolean logged = false;
if (cause instanceof CentralDogmaException) {
if (cause instanceof EntryNotFoundException) {
if (!initialValueFuture.isDone() && errorOnEntryNotFound) {
initialValueFuture.completeExceptionally(thrown);
close();
return null;
}
logger.info("{}/{}{} does not exist yet; trying again",
projectName, repositoryName, pathPattern);
logged = true;
} else if (cause instanceof RepositoryNotFoundException) {
logger.info("{}/{} does not exist yet; trying again",
projectName, repositoryName);
logged = true;
}
}
if (cause instanceof CancellationException) {
// Cancelled by close()
return null;
}
if (!logged) {
logger.warn("Failed to watch a file ({}/{}{}) at Central Dogma; trying again",
projectName, repositoryName, pathPattern, cause);
}
scheduleWatch(numAttemptsSoFar + 1);
} catch (Throwable t) {
logger.error("Unexpected exception while watching a file at Central Dogma:", t);
}
return null;
});
}
abstract CompletableFuture> doWatch(Revision lastKnownRevision);
private void notifyListeners(Latest latest) {
if (isStopped()) {
// Do not notify after stopped.
return;
}
for (Map.Entry, Executor> entry : updateListeners) {
final BiConsumer listener = entry.getKey();
final Executor executor = entry.getValue();
executor.execute(() -> {
try {
listener.accept(latest.revision(), latest.value());
} catch (Exception e) {
logger.warn("Exception thrown for watcher ({}/{}{}): rev={}",
projectName, repositoryName, pathPattern, latest.revision(), e);
}
});
}
}
@Override
public String toString() {
return MoreObjects.toStringHelper(this).omitNullValues()
.add("watchScheduler", watchScheduler)
.add("projectName", projectName)
.add("repositoryName", repositoryName)
.add("pathPattern", pathPattern)
.add("errorOnEntryNotFound", errorOnEntryNotFound)
.add("delayOnSuccessMillis", delayOnSuccessMillis)
.add("initialDelayMillis", initialDelayMillis)
.add("maxDelayMillis", maxDelayMillis)
.add("multiplier", multiplier)
.add("jitterRate", jitterRate)
.add("latest", latest)
.toString();
}
}