Optimize PermissionCollection to delay listing emails

The email addresses are only necessary if a ref pattern
containing ${username} pertains to an access request made
by the caller.

If patterns are not user-specific (e.g. refs/heads/*),
it is safe to skip loading emails from the AccountState
and Realm objects.

Change-Id: Id801dd637f69f1983bf28268654923099933817a

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

@@ -24,6 +24,7 @@ import com.google.gerrit.common.data.PermissionRule;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.inject.Inject;
+import com.google.inject.Provider;
 import com.google.inject.Singleton;
 
 import java.util.ArrayList;
@@ -60,23 +61,22 @@ public class PermissionCollection {
      *        priority order (project specific definitions must appear before
      *        inherited ones).
      * @param ref reference being accessed.
-     * @param usernames if the reference is a per-user reference, access sections
-     *        using the parameter variable "${username}" will first have each of
-     *        {@code usernames} inserted into them before seeing if they apply to
-     *        the reference named by {@code ref}. If null or empty, per-user
-     *        references are ignored.
+     * @param usernameProvider if the reference is a per-user reference, access
+     *        sections using the parameter variable "${username}" will first
+     *        have each of {@code usernames} inserted into them before seeing if
+     *        they apply to the reference named by {@code ref}.
      * @return map of permissions that apply to this reference, keyed by
      *         permission name.
      */
     PermissionCollection filter(Iterable<SectionMatcher> matcherList,
-        String ref, Collection<String> usernames) {
+        String ref, Provider<? extends Collection<String>> usernameProvider) {
       if (isRE(ref)) {
         ref = RefControl.shortestExample(ref);
       } else if (ref.endsWith("/*")) {
         ref = ref.substring(0, ref.length() - 1);
       }
 
-      boolean hasUsernames = usernames != null && !usernames.isEmpty();
+      Collection<String> usernames = null;
       boolean perUser = false;
       Map<AccessSection, Project.NameKey> sectionToProject = Maps.newLinkedHashMap();
       for (SectionMatcher sm : matcherList) {
@@ -92,9 +92,13 @@ public class PermissionCollection {
         // that will never be shared with non-user references, and the per-user
         // references are usually less frequent than the non-user references.
         //
-        if (hasUsernames) {
-          if (!perUser && sm.matcher instanceof RefPatternMatcher.ExpandParameters) {
-            perUser = ((RefPatternMatcher.ExpandParameters) sm.matcher).matchPrefix(ref);
+        if (sm.matcher instanceof RefPatternMatcher.ExpandParameters) {
+          if (!((RefPatternMatcher.ExpandParameters) sm.matcher).matchPrefix(ref)) {
+            continue;
+          }
+          perUser = true;
+          if (usernames == null) {
+            usernames = usernameProvider.get();
           }
           for (String username : usernames) {
             if (sm.match(ref, username)) {

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

@@ -14,7 +14,6 @@
 
 package com.google.gerrit.server.project;
 
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.gerrit.common.Nullable;
@@ -57,6 +56,7 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
@@ -207,15 +207,25 @@ public class ProjectControl {
     }
     RefControl ctl = refControls.get(refName);
     if (ctl == null) {
-      ImmutableList.Builder<String> usernames = ImmutableList.<String> builder();
-      if (user.getUserName() != null) {
-        usernames.add(user.getUserName());
-      }
-      if (user instanceof IdentifiedUser) {
-        usernames.addAll(((IdentifiedUser) user).getEmailAddresses());
-      }
+      Provider<List<String>> usernames = new Provider<List<String>>() {
+        @Override
+        public List<String> get() {
+          List<String> r;
+          if (user.isIdentifiedUser()) {
+            Set<String> emails = ((IdentifiedUser) user).getEmailAddresses();
+            r = new ArrayList<>(emails.size() + 1);
+            r.addAll(emails);
+          } else {
+            r = new ArrayList<>(1);
+          }
+          if (user.getUserName() != null) {
+            r.add(user.getUserName());
+          }
+          return r;
+        }
+      };
       PermissionCollection relevant =
-          permissionFilter.filter(access(), refName, usernames.build());
+          permissionFilter.filter(access(), refName, usernames);
       ctl = new RefControl(this, refName, relevant);
       refControls.put(refName, ctl);
     }