Index: Extract common parts into AbstractVersionManager

Most of code in LuceneVersionManager and ElasticVersionManager is
similar. The only difference is in the way how both implementation get
current version of schema. This patch extract common parts into
AbstracttVersionManager and refactor both classes to use common parent.

Change-Id: I170e16073b03f648e9904401b0b42b807891d471

gerrit-server/src/main/java/com/google/gerrit/server/index/AbstractVersionManager.java

@@ -0,0 +1,223 @@
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.server.index;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.gerrit.extensions.events.LifecycleListener;
+import com.google.gerrit.server.config.GerritServerConfig;
+import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.index.IndexDefinition.IndexFactory;
+import com.google.inject.ProvisionException;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.lib.Config;
+
+public abstract class AbstractVersionManager implements LifecycleListener {
+  public static class Version<V> {
+    public final Schema<V> schema;
+    public final int version;
+    public final boolean ready;
+
+    public Version(Schema<V> schema, int version, boolean ready) {
+      checkArgument(schema == null || schema.getVersion() == version);
+      this.schema = schema;
+      this.version = version;
+      this.ready = ready;
+    }
+  }
+
+  protected final boolean onlineUpgrade;
+  protected final String runReindexMsg;
+  protected final SitePaths sitePaths;
+  protected final Map<String, IndexDefinition<?, ?, ?>> defs;
+  protected final Map<String, OnlineReindexer<?, ?, ?>> reindexers;
+
+  protected AbstractVersionManager(
+      @GerritServerConfig Config cfg,
+      SitePaths sitePaths,
+      Collection<IndexDefinition<?, ?, ?>> defs) {
+    this.sitePaths = sitePaths;
+    this.defs = Maps.newHashMapWithExpectedSize(defs.size());
+    for (IndexDefinition<?, ?, ?> def : defs) {
+      this.defs.put(def.getName(), def);
+    }
+
+    reindexers = Maps.newHashMapWithExpectedSize(defs.size());
+    onlineUpgrade = cfg.getBoolean("index", null, "onlineUpgrade", true);
+    runReindexMsg =
+        "No index versions ready; run java -jar "
+            + sitePaths.gerrit_war.toAbsolutePath()
+            + " reindex";
+  }
+
+  @Override
+  public void start() {
+    GerritIndexStatus cfg = createIndexStatus();
+    for (IndexDefinition<?, ?, ?> def : defs.values()) {
+      initIndex(def, cfg);
+    }
+  }
+
+  @Override
+  public void stop() {
+    // Do nothing; indexes are closed on demand by IndexCollection.
+  }
+
+  /**
+   * Start the online reindexer if the current index is not already the latest.
+   *
+   * @param name index name
+   * @param force start re-index
+   * @return true if started, otherwise false.
+   * @throws ReindexerAlreadyRunningException
+   */
+  public synchronized boolean startReindexer(String name, boolean force)
+      throws ReindexerAlreadyRunningException {
+    OnlineReindexer<?, ?, ?> reindexer = reindexers.get(name);
+    validateReindexerNotRunning(reindexer);
+    if (force || !isLatestIndexVersion(name, reindexer)) {
+      reindexer.start();
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Activate the latest index if the current index is not already the latest.
+   *
+   * @param name index name
+   * @return true if index was activated, otherwise false.
+   * @throws ReindexerAlreadyRunningException
+   */
+  public synchronized boolean activateLatestIndex(String name)
+      throws ReindexerAlreadyRunningException {
+    OnlineReindexer<?, ?, ?> reindexer = reindexers.get(name);
+    validateReindexerNotRunning(reindexer);
+    if (!isLatestIndexVersion(name, reindexer)) {
+      reindexer.activateIndex();
+      return true;
+    }
+    return false;
+  }
+
+  protected <K, V, I extends Index<K, V>> void initIndex(
+      IndexDefinition<K, V, I> def, GerritIndexStatus cfg) {
+    TreeMap<Integer, Version<V>> versions = scanVersions(def, cfg);
+    // Search from the most recent ready version.
+    // Write to the most recent ready version and the most recent version.
+    Version<V> search = null;
+    List<Version<V>> write = Lists.newArrayListWithCapacity(2);
+    for (Version<V> v : versions.descendingMap().values()) {
+      if (v.schema == null) {
+        continue;
+      }
+      if (write.isEmpty() && onlineUpgrade) {
+        write.add(v);
+      }
+      if (v.ready) {
+        search = v;
+        if (!write.contains(v)) {
+          write.add(v);
+        }
+        break;
+      }
+    }
+    if (search == null) {
+      throw new ProvisionException(runReindexMsg);
+    }
+
+    IndexFactory<K, V, I> factory = def.getIndexFactory();
+    I searchIndex = factory.create(search.schema);
+    IndexCollection<K, V, I> indexes = def.getIndexCollection();
+    indexes.setSearchIndex(searchIndex);
+    for (Version<V> v : write) {
+      if (v.version != search.version) {
+        indexes.addWriteIndex(factory.create(v.schema));
+      } else {
+        indexes.addWriteIndex(searchIndex);
+      }
+    }
+
+    markNotReady(def.getName(), versions.values(), write);
+
+    synchronized (this) {
+      if (!reindexers.containsKey(def.getName())) {
+        int latest = write.get(0).version;
+        OnlineReindexer<K, V, I> reindexer = new OnlineReindexer<>(def, latest);
+        reindexers.put(def.getName(), reindexer);
+        if (onlineUpgrade && latest != search.version) {
+          reindexer.start();
+        }
+      }
+    }
+  }
+
+  protected GerritIndexStatus createIndexStatus() {
+    try {
+      return new GerritIndexStatus(sitePaths);
+    } catch (ConfigInvalidException | IOException e) {
+      throw fail(e);
+    }
+  }
+
+  protected abstract <V> boolean isDirty(Collection<Version<V>> inUse, Version<V> v);
+
+  protected abstract <K, V, I extends Index<K, V>> TreeMap<Integer, Version<V>> scanVersions(
+      IndexDefinition<K, V, I> def, GerritIndexStatus cfg);
+
+  private boolean isLatestIndexVersion(String name, OnlineReindexer<?, ?, ?> reindexer) {
+    int readVersion = defs.get(name).getIndexCollection().getSearchIndex().getSchema().getVersion();
+    return reindexer == null || reindexer.getVersion() == readVersion;
+  }
+
+  private static void validateReindexerNotRunning(OnlineReindexer<?, ?, ?> reindexer)
+      throws ReindexerAlreadyRunningException {
+    if (reindexer != null && reindexer.isRunning()) {
+      throw new ReindexerAlreadyRunningException();
+    }
+  }
+
+  private <V> void markNotReady(
+      String name, Iterable<Version<V>> versions, Collection<Version<V>> inUse) {
+    GerritIndexStatus cfg = createIndexStatus();
+    boolean dirty = false;
+    for (Version<V> v : versions) {
+      if (isDirty(inUse, v)) {
+        cfg.setReady(name, v.version, false);
+        dirty = true;
+      }
+    }
+    if (dirty) {
+      try {
+        cfg.save();
+      } catch (IOException e) {
+        throw fail(e);
+      }
+    }
+  }
+
+  private ProvisionException fail(Throwable t) {
+    ProvisionException e = new ProvisionException("Error scanning indexes");
+    e.initCause(t);
+    return e;
+  }
+}