Load user's starred changes async to query

Some database implementations are able to run a query in the
background and only stall the application when the ResultSet is
iterated and the next object has not yet been returned.

If the caller is signed in and running a change query the JSON
formatter will need to use the starred change collection.  Begin
loading the starred change collection for the caller before the
change query is parsed and executed, giving the database time to
load the starred changes in the background.

This should reduce some search result latency for signed in users
on gerrit-review, where the database is slow but ResultSet loads
objects async to the application.

Change-Id: Ic19c3242d2fc34f5e4417989667beb51c0d6260d

gerrit-server/src/main/java/com/google/gerrit/server/IdentifiedUser.java

@@ -15,6 +15,7 @@
 package com.google.gerrit.server;
 
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
 import com.google.gerrit.common.data.AccountInfo;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.AccountDiffPreference;
@@ -34,6 +35,7 @@ import com.google.gerrit.server.config.AnonymousCowardName;
 import com.google.gerrit.server.config.AuthConfig;
 import com.google.gerrit.server.config.CanonicalWebUrl;
 import com.google.gwtorm.server.OrmException;
+import com.google.gwtorm.server.ResultSet;
 import com.google.inject.Inject;
 import com.google.inject.OutOfScopeException;
 import com.google.inject.Provider;
@@ -53,7 +55,6 @@ import java.net.URL;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.TimeZone;
@@ -195,6 +196,7 @@ public class IdentifiedUser extends CurrentUser {
   private Set<String> emailAddresses;
   private GroupMembership effectiveGroups;
   private Set<Change.Id> starredChanges;
+  private ResultSet<StarredChange> starredQuery;
   private Collection<AccountProjectWatch> notificationFilters;
   private CurrentUser realUser;
 
@@ -296,11 +298,18 @@ public class IdentifiedUser extends CurrentUser {
       if (dbProvider == null) {
         throw new OutOfScopeException("Not in request scoped user");
       }
-      final Set<Change.Id> h = new HashSet<Change.Id>();
+      Set<Change.Id> h = Sets.newHashSet();
       try {
-        for (final StarredChange sc : dbProvider.get().starredChanges()
-            .byAccount(getAccountId())) {
-          h.add(sc.getChangeId());
+        if (starredQuery != null) {
+          for (StarredChange sc : starredQuery) {
+            h.add(sc.getChangeId());
+          }
+          starredQuery = null;
+        } else {
+          for (StarredChange sc : dbProvider.get().starredChanges()
+              .byAccount(getAccountId())) {
+            h.add(sc.getChangeId());
+          }
         }
       } catch (OrmException e) {
         log.warn("Cannot query starred by user changes", e);
@@ -310,6 +319,29 @@ public class IdentifiedUser extends CurrentUser {
     return starredChanges;
   }
 
+  public void asyncStarredChanges() {
+    if (starredChanges == null && dbProvider != null) {
+      try {
+        starredQuery =
+            dbProvider.get().starredChanges().byAccount(getAccountId());
+      } catch (OrmException e) {
+        log.warn("Cannot query starred by user changes", e);
+        starredQuery = null;
+        starredChanges = Collections.emptySet();
+      }
+    }
+  }
+
+  public void abortStarredChanges() {
+    if (starredQuery != null) {
+      try {
+        starredQuery.close();
+      } finally {
+        starredQuery = null;
+      }
+    }
+  }
+
   @Override
   public Collection<AccountProjectWatch> getNotificationFilters() {
     if (notificationFilters == null) {

gerrit-server/src/main/java/com/google/gerrit/server/query/change/QueryChanges.java

@@ -20,12 +20,15 @@ import com.google.gerrit.extensions.restapi.AuthException;
 import com.google.gerrit.extensions.restapi.BadRequestException;
 import com.google.gerrit.extensions.restapi.RestReadView;
 import com.google.gerrit.extensions.restapi.TopLevelResource;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.change.ChangeJson;
 import com.google.gerrit.server.change.ChangeJson.ChangeInfo;
 import com.google.gerrit.server.project.ChangeControl;
 import com.google.gerrit.server.query.QueryParseException;
 import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
+import com.google.inject.Provider;
 
 import org.kohsuke.args4j.Option;
 
@@ -39,6 +42,7 @@ import java.util.regex.Pattern;
 public class QueryChanges implements RestReadView<TopLevelResource> {
   private final ChangeJson json;
   private final QueryProcessor imp;
+  private final Provider<CurrentUser> user;
   private boolean reverse;
   private EnumSet<ListChangesOption> options;
 
@@ -80,9 +84,11 @@ public class QueryChanges implements RestReadView<TopLevelResource> {
   @Inject
   QueryChanges(ChangeJson json,
       QueryProcessor qp,
-      ChangeControl.Factory cf) {
+      ChangeControl.Factory cf,
+      Provider<CurrentUser> user) {
     this.json = json;
     this.imp = qp;
+    this.user = user;
 
     options = EnumSet.noneOf(ListChangesOption.class);
     json.setChangeControlFactory(cf);
@@ -127,6 +133,22 @@ public class QueryChanges implements RestReadView<TopLevelResource> {
       throw new QueryParseException("limit of 10 queries");
     }
 
+    IdentifiedUser self = null;
+    try {
+      if (user.get().isIdentifiedUser()) {
+        self = (IdentifiedUser) user.get();
+        self.asyncStarredChanges();
+      }
+      return query0();
+    } finally {
+      if (self != null) {
+        self.abortStarredChanges();
+      }
+    }
+  }
+
+  private List<List<ChangeInfo>> query0() throws OrmException,
+      QueryParseException {
     int cnt = queries.size();
     BitSet more = new BitSet(cnt);
     List<List<ChangeData>> data = Lists.newArrayListWithCapacity(cnt);