pkuwm commented on a change in pull request #775: Add HttpRoutingDataReader URL: https://github.com/apache/helix/pull/775#discussion_r383443072
########## File path: zookeeper-api/src/main/java/org/apache/helix/zookeeper/util/HttpRoutingDataReader.java ########## @@ -0,0 +1,134 @@ +package org.apache.helix.zookeeper.util; + +/* + * 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. + */ + +import java.io.IOException; +import java.util.Collections; +import java.util.List; +import java.util.Map; +import java.util.concurrent.TimeUnit; +import java.util.stream.Collectors; + +import com.jcabi.aspects.RetryOnFailure; +import org.apache.helix.msdcommon.constant.MetadataStoreRoutingConstants; +import org.apache.helix.msdcommon.datamodel.MetadataStoreRoutingData; +import org.apache.helix.msdcommon.datamodel.TrieRoutingData; +import org.apache.helix.msdcommon.exception.InvalidRoutingDataException; +import org.apache.http.HttpEntity; +import org.apache.http.client.methods.CloseableHttpResponse; +import org.apache.http.client.methods.HttpGet; +import org.apache.http.impl.client.CloseableHttpClient; +import org.apache.http.impl.client.HttpClients; +import org.apache.http.util.EntityUtils; +import org.codehaus.jackson.map.ObjectMapper; + + +public class HttpRoutingDataReader { + private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper(); + private static volatile Map<String, List<String>> _rawRoutingData; + private static volatile MetadataStoreRoutingData _metadataStoreRoutingData; + + /** + * This class is a Singleton. + */ + private HttpRoutingDataReader() { + } + + /** + * Fetches routing data from the data source via HTTP. + * @return a mapping from "metadata store realm addresses" to lists of + * "metadata store sharding keys", where the sharding keys in a value list all route to + * the realm address in the key disallows a meaningful mapping to be returned + */ + @RetryOnFailure(attempts = 3, delay = 1, unit = TimeUnit.SECONDS) + public static Map<String, List<String>> getRawRoutingData() + throws IOException { + if (_rawRoutingData == null) { + synchronized (HttpRoutingDataReader.class) { + if (_rawRoutingData == null) { + String msdsEndpoint = + System.getProperty(MetadataStoreRoutingConstants.MSDS_SERVER_ENDPOINT_KEY); + if (msdsEndpoint == null || msdsEndpoint.isEmpty()) { + throw new IllegalStateException( + "HttpRoutingDataReader was unable to find a valid MSDS endpoint String in System Properties!"); + } + + // Note: HttpClient's timeout settings are system timeout settings by default + CloseableHttpClient httpClient = HttpClients.createDefault(); Review comment: - `@RetryOnFailure` is applied to this whole method. It seems we are going to call this reader each time we create a RealmAwareZkClient? The heavy work is one the first time we call to get routing data. I would use HttpClients' retry so we don't have to acquire lock and create HttpClient 3 times (a bit heavier) if attempting. Instead, http client could just retry on exception within the locking block, which I think is easier. What do you think? - When is reader supposed to be created, each time when creating zkClient, or a singleton is maintained ? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
