ivankelly commented on a change in pull request #1577: Metadata Update mechanism URL: https://github.com/apache/bookkeeper/pull/1577#discussion_r207799848
########## File path: bookkeeper-server/src/main/java/org/apache/bookkeeper/client/MetadataUpdateLoop.java ########## @@ -0,0 +1,185 @@ +/** + * 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.bookkeeper.client; + +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.atomic.AtomicInteger; +import java.util.function.BiPredicate; +import java.util.function.Function; +import java.util.function.Supplier; + +import org.apache.bookkeeper.meta.LedgerManager; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * Mechanism to safely update the metadata of a ledger. + * + * <p>The loop takes the following steps: + * 1. Check if the metadata needs to be changed. + * 2. Make a copy of the metadata and modify it. + * 3. Write the modified copy to zookeeper. + * 3.1 If the write succeeds, go to 6. + * 3.2 If the write fails because of a failed compare and swap, go to 4. + * 4. Read the metadata back from the store + * 5. Update the local copy of the metadata with the metadata read in 4, go to 1. + * 6. Update the local copy of the metadata with the metadata which has just been written. + * + * <p>All mutating operations are compare and swap operation. If the compare fails, another + * iteration of the loop begins. + */ +class MetadataUpdateLoop { + static final Logger LOG = LoggerFactory.getLogger(MetadataUpdateLoop.class); + + private final LedgerManager lm; + private final long ledgerId; + private final Supplier<LedgerMetadata> currentLocalValue; + private final NeedsUpdatePredicate needsTransformation; + private final Function<LedgerMetadata, LedgerMetadata> transform; + private final BiPredicate<LedgerMetadata, LedgerMetadata> updateLocalValue; + + private final String logContext; + private final AtomicInteger writeLoopCounter = new AtomicInteger(0); Review comment: Changed ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
