Add background job to abandon inactive changes automatically

Add a change cleanup job that runs periodically in the background.
This cleanup job can automatically abandon open changes that have been
inactive for a defined time.

Abandoning old inactive changes has a few advantages:
- it reduces the load for recomputing the mergeability flag when a
  change is merged
- it keeps dashboards clean
- it signals change authors that changes are considered outdated

Change-Id: Ia798667901fe8d734ca29bcf81c7b9b4a1eb4c50
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/change/AbandonUtil.java

@@ -0,0 +1,97 @@
+// Copyright (C) 2015 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.change;
+
+import com.google.gerrit.extensions.restapi.ResourceConflictException;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.config.ChangeCleanupConfig;
+import com.google.gerrit.server.project.ChangeControl;
+import com.google.gerrit.server.project.NoSuchChangeException;
+import com.google.gerrit.server.query.QueryParseException;
+import com.google.gerrit.server.query.change.ChangeData;
+import com.google.gerrit.server.query.change.ChangeQueryBuilder;
+import com.google.gerrit.server.query.change.QueryProcessor;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+@Singleton
+public class AbandonUtil {
+  private static final Logger log = LoggerFactory.getLogger(AbandonUtil.class);
+
+  private final ChangeCleanupConfig cfg;
+  private final IdentifiedUser.GenericFactory identifiedUserFactory;
+  private final QueryProcessor queryProcessor;
+  private final ChangeQueryBuilder queryBuilder;
+  private final ChangeControl.GenericFactory changeControlFactory;
+  private final Abandon abandon;
+
+  @Inject
+  AbandonUtil(
+      ChangeCleanupConfig cfg,
+      IdentifiedUser.GenericFactory identifiedUserFactory,
+      QueryProcessor queryProcessor,
+      ChangeQueryBuilder queryBuilder,
+      ChangeControl.GenericFactory changeControlFactory,
+      Abandon abandon) {
+    this.cfg = cfg;
+    this.identifiedUserFactory = identifiedUserFactory;
+    this.queryProcessor = queryProcessor;
+    this.queryBuilder = queryBuilder;
+    this.changeControlFactory = changeControlFactory;
+    this.abandon = abandon;
+  }
+
+  public void abandonInactiveOpenChanges() {
+    if (cfg.getAbandonAfter() <= 0) {
+      return;
+    }
+
+    try {
+      String query = "status:new age:"
+          + TimeUnit.MILLISECONDS.toMinutes(cfg.getAbandonAfter())
+          + "m";
+      List<ChangeData> changesToAbandon = queryProcessor.enforceVisibility(false)
+          .queryChanges(queryBuilder.parse(query)).changes();
+      for (ChangeData cd : changesToAbandon) {
+        try {
+          abandon.abandon(changeControl(cd), cfg.getAbandonMessage(), null);
+        } catch (ResourceConflictException e) {
+          // Change was already merged or abandoned.
+        } catch (Throwable e) {
+          log.error(String.format(
+              "Failed to auto-abandon inactive open change %d.",
+                  cd.getId().get()), e);
+        }
+      }
+    } catch (QueryParseException | OrmException e) {
+      log.error("Failed to query inactive open changes for auto-abandoning.", e);
+    }
+  }
+
+  private ChangeControl changeControl(ChangeData cd)
+      throws NoSuchChangeException, OrmException {
+    Change c = cd.change();
+    return changeControlFactory.controlFor(c,
+        identifiedUserFactory.create(c.getOwner()));
+  }
+}