kafka Snapshot 源码
kafka Snapshot 代码
文件路径:/metadata/src/main/java/org/apache/kafka/timeline/Snapshot.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF 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
*
* 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 org.apache.kafka.timeline;
import java.util.IdentityHashMap;
import java.util.Map;
/**
* A snapshot of some timeline data structures.
*
* The snapshot contains historical data for several timeline data structures.
* We use an IdentityHashMap to store this data. This way, we can easily drop all of
* the snapshot data.
*/
class Snapshot {
private final long epoch;
private IdentityHashMap<Revertable, Delta> map = new IdentityHashMap<>(4);
private Snapshot prev = this;
private Snapshot next = this;
Snapshot(long epoch) {
this.epoch = epoch;
}
long epoch() {
return epoch;
}
@SuppressWarnings("unchecked")
<T extends Delta> T getDelta(Revertable owner) {
return (T) map.get(owner);
}
void setDelta(Revertable owner, Delta delta) {
map.put(owner, delta);
}
void handleRevert() {
for (Map.Entry<Revertable, Delta> entry : map.entrySet()) {
entry.getKey().executeRevert(epoch, entry.getValue());
}
}
void mergeFrom(Snapshot source) {
// Merge the deltas from the source snapshot into this snapshot.
for (Map.Entry<Revertable, Delta> entry : source.map.entrySet()) {
// We first try to just copy over the object reference. That will work if
//we have no entry at all for the given Revertable.
Delta destinationDelta = map.putIfAbsent(entry.getKey(), entry.getValue());
if (destinationDelta != null) {
// If we already have an entry for the Revertable, we need to merge the
// source delta into our delta.
destinationDelta.mergeFrom(epoch, entry.getValue());
}
}
// Delete the source snapshot to make sure nobody tries to reuse it. We might now
// share some delta entries with it.
source.erase();
}
Snapshot prev() {
return prev;
}
Snapshot next() {
return next;
}
void appendNext(Snapshot newNext) {
newNext.prev = this;
newNext.next = next;
next.prev = newNext;
next = newNext;
}
void erase() {
map = null;
next.prev = prev;
prev.next = next;
prev = this;
next = this;
}
}
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