Fix email delivery for merged notifications

There was no ReviewDb available to the email thread. Fix this by
using the same pattern as PostReview; a task is built from a factory
and the task sets up its own thread-local request scope to provide
a dynamic ReviewDb instance to the MergedSender.

Change-Id: Idbeb0d0f611efbd6c1409c5da57bd7408eb89019

gerrit-server/src/main/java/com/google/gerrit/server/git/EmailMerge.java

@@ -0,0 +1,120 @@
+// 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.git;
+
+import com.google.gerrit.common.Nullable;
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.change.EmailReviewComments;
+import com.google.gerrit.server.mail.MergedSender;
+import com.google.gerrit.server.util.RequestContext;
+import com.google.gerrit.server.util.ThreadLocalRequestContext;
+import com.google.gwtorm.server.OrmException;
+import com.google.gwtorm.server.SchemaFactory;
+import com.google.inject.Inject;
+import com.google.inject.OutOfScopeException;
+import com.google.inject.Provider;
+import com.google.inject.ProvisionException;
+import com.google.inject.assistedinject.Assisted;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.ExecutorService;
+
+public class EmailMerge implements Runnable, RequestContext {
+  private static final Logger log = LoggerFactory.getLogger(EmailReviewComments.class);
+
+  public interface Factory {
+    EmailMerge create(Change.Id changeId, Account.Id submitter);
+  }
+
+  private final ExecutorService sendEmailsExecutor;
+  private final MergedSender.Factory mergedSenderFactory;
+  private final SchemaFactory<ReviewDb> schemaFactory;
+  private final ThreadLocalRequestContext requestContext;
+
+  private final Change.Id changeId;
+  private final Account.Id submitter;
+  private ReviewDb db;
+
+  @Inject
+  EmailMerge(@EmailReviewCommentsExecutor ExecutorService executor,
+      MergedSender.Factory mergedSenderFactory,
+      SchemaFactory<ReviewDb> schemaFactory,
+      ThreadLocalRequestContext requestContext,
+      @Assisted Change.Id changeId,
+      @Assisted @Nullable Account.Id submitter) {
+    this.sendEmailsExecutor = executor;
+    this.mergedSenderFactory = mergedSenderFactory;
+    this.schemaFactory = schemaFactory;
+    this.requestContext = requestContext;
+    this.changeId = changeId;
+    this.submitter = submitter;
+  }
+
+  void sendAsync() {
+    sendEmailsExecutor.submit(this);
+  }
+
+  @Override
+  public void run() {
+    RequestContext old = requestContext.setContext(this);
+    try {
+      MergedSender cm = mergedSenderFactory.create(changeId);
+      if (submitter != null) {
+        cm.setFrom(submitter);
+      }
+      cm.send();
+    } catch (Exception e) {
+      log.error("Cannot email merged notification for " + changeId, e);
+    } finally {
+      requestContext.setContext(old);
+      if (db != null) {
+        db.close();
+        db = null;
+      }
+    }
+  }
+
+  @Override
+  public String toString() {
+    return "send-email merged";
+  }
+
+  @Override
+  public CurrentUser getCurrentUser() {
+    throw new OutOfScopeException("No user on email thread");
+  }
+
+  @Override
+  public Provider<ReviewDb> getReviewDbProvider() {
+    return new Provider<ReviewDb>() {
+      @Override
+      public ReviewDb get() {
+        if (db == null) {
+          try {
+            db = schemaFactory.open();
+          } catch (OrmException e) {
+            throw new ProvisionException("Cannot open ReviewDb", e);
+          }
+        }
+        return db;
+      }
+    };
+  }
+}