| /* |
| * 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.hadoop.hbase.master; |
| |
| import java.io.IOException; |
| import java.util.concurrent.atomic.AtomicBoolean; |
| import java.util.concurrent.atomic.AtomicInteger; |
| import org.apache.hadoop.conf.Configuration; |
| import org.apache.hadoop.fs.FileSystem; |
| import org.apache.hadoop.fs.Path; |
| import org.apache.hadoop.hbase.ClusterId; |
| import org.apache.hadoop.hbase.Server; |
| import org.apache.hadoop.hbase.util.CommonFSUtils; |
| import org.apache.hadoop.hbase.util.FSUtils; |
| import org.apache.yetus.audience.InterfaceAudience; |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| import org.apache.hbase.thirdparty.com.google.common.base.Preconditions; |
| |
| /** |
| * Caches the cluster ID of the cluster. For standby masters, this is used to serve the client |
| * RPCs that fetch the cluster ID. ClusterID is only created by an active master if one does not |
| * already exist. Standby masters just read the information from the file system. This class is |
| * thread-safe. |
| * |
| * TODO: Make it a singleton without affecting concurrent junit tests. |
| */ |
| @InterfaceAudience.Private |
| public class CachedClusterId { |
| |
| public static final Logger LOG = LoggerFactory.getLogger(CachedClusterId.class); |
| private static final int MAX_FETCH_TIMEOUT_MS = 10000; |
| |
| private final Path rootDir; |
| private final FileSystem fs; |
| |
| // When true, indicates that a FileSystem fetch of ClusterID is in progress. This is used to |
| // avoid multiple fetches from FS and let only one thread fetch the information. |
| AtomicBoolean fetchInProgress = new AtomicBoolean(false); |
| |
| // When true, it means that the cluster ID has been fetched successfully from fs. |
| private AtomicBoolean isClusterIdSet = new AtomicBoolean(false); |
| // Immutable once set and read multiple times. |
| private ClusterId clusterId; |
| |
| private final Server server; |
| |
| // cache stats for testing. |
| private AtomicInteger cacheMisses = new AtomicInteger(0); |
| |
| public CachedClusterId(Server server, Configuration conf) throws IOException { |
| this.rootDir = CommonFSUtils.getRootDir(conf); |
| this.fs = rootDir.getFileSystem(conf); |
| this.server = server; |
| } |
| |
| /** |
| * Succeeds only once, when setting to a non-null value. Overwrites are not allowed. |
| */ |
| private void setClusterId(ClusterId id) { |
| if (id == null || isClusterIdSet.get()) { |
| return; |
| } |
| clusterId = id; |
| isClusterIdSet.set(true); |
| } |
| |
| /** |
| * Returns a cached copy of the cluster ID. null if the cache is not populated. |
| */ |
| private String getClusterId() { |
| if (!isClusterIdSet.get()) { |
| return null; |
| } |
| // It is ok to read without a lock since clusterId is immutable once set. |
| return clusterId.toString(); |
| } |
| |
| /** |
| * Attempts to fetch the cluster ID from the file system. If no attempt is already in progress, |
| * synchronously fetches the cluster ID and sets it. If an attempt is already in progress, |
| * returns right away and the caller is expected to wait for the fetch to finish. |
| * @return true if the attempt is done, false if another thread is already fetching it. |
| */ |
| private boolean attemptFetch() { |
| if (fetchInProgress.compareAndSet(false, true)) { |
| // A fetch is not in progress, so try fetching the cluster ID synchronously and then notify |
| // the waiting threads. |
| try { |
| cacheMisses.incrementAndGet(); |
| setClusterId(FSUtils.getClusterId(fs, rootDir)); |
| } catch (IOException e) { |
| LOG.warn("Error fetching cluster ID", e); |
| } finally { |
| Preconditions.checkState(fetchInProgress.compareAndSet(true, false)); |
| synchronized (fetchInProgress) { |
| fetchInProgress.notifyAll(); |
| } |
| } |
| return true; |
| } |
| return false; |
| } |
| |
| private void waitForFetchToFinish() throws InterruptedException { |
| synchronized (fetchInProgress) { |
| while (fetchInProgress.get()) { |
| // We don't want the fetches to block forever, for example if there are bugs |
| // of missing notifications. |
| fetchInProgress.wait(MAX_FETCH_TIMEOUT_MS); |
| } |
| } |
| } |
| |
| /** |
| * Fetches the ClusterId from FS if it is not cached locally. Atomically updates the cached |
| * copy and is thread-safe. Optimized to do a single fetch when there are multiple threads are |
| * trying get from a clean cache. |
| * |
| * @return ClusterId by reading from FileSystem or null in any error case or cluster ID does |
| * not exist on the file system or if the server initiated a tear down. |
| */ |
| public String getFromCacheOrFetch() { |
| if (server.isStopping() || server.isStopped()) { |
| return null; |
| } |
| String id = getClusterId(); |
| if (id != null) { |
| return id; |
| } |
| if (!attemptFetch()) { |
| // A fetch is in progress. |
| try { |
| waitForFetchToFinish(); |
| } catch (InterruptedException e) { |
| // pass and return whatever is in the cache. |
| } |
| } |
| return getClusterId(); |
| } |
| |
| public int getCacheStats() { |
| return cacheMisses.get(); |
| } |
| } |