Add option to load project cache at server startup

In installations with large numbers of projects, it may take a long
time to populate the cache. Allow the option of concurrently loading
the project cache during server startup.

Test result:

- 5700 projects
- Using 40 cpus

Without this change, loading the cache takes about 2 minutes.
With this change, loading the cache takes a few seconds.

Change-Id: Ic05cc8b88ee4c4bf6f5028d3f4dec1e32872aef5

gerrit-server/src/main/java/com/google/gerrit/server/project/ProjectCacheImpl.java

@@ -18,9 +18,11 @@ import com.google.common.base.Throwables;
 import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
 import com.google.common.collect.Sets;
+import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.server.cache.CacheModule;
+import com.google.gerrit.server.project.ProjectCacheWarmer;
 import com.google.gerrit.server.config.AllProjectsName;
 import com.google.gerrit.server.config.AllUsersName;
 import com.google.gerrit.server.git.GitRepositoryManager;
@@ -29,6 +31,7 @@ import com.google.inject.Inject;
 import com.google.inject.Module;
 import com.google.inject.Singleton;
 import com.google.inject.TypeLiteral;
+import com.google.inject.internal.UniqueAnnotations;
 import com.google.inject.name.Named;
 
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
@@ -70,6 +73,9 @@ public class ProjectCacheImpl implements ProjectCache {
 
         bind(ProjectCacheImpl.class);
         bind(ProjectCache.class).to(ProjectCacheImpl.class);
+        bind(LifecycleListener.class)
+          .annotatedWith(UniqueAnnotations.create())
+          .to(ProjectCacheWarmer.class);
       }
     };
   }