Revert "Remove unused CurrentUser#cacheKey method"

Revert "Adjust to changes in Gerrit core"

Revert submission 283559-currentuser-remove-cache-key

Reason for revert: Causes a latency regression for some hosts
Reverted Changes:
I76bfd3ebc:Adjust to changes in Gerrit core
If7ccfd9a4:Remove unused CurrentUser#cacheKey method
I1378ad083:Remove PerThreadCache

Change-Id: Idd9eb9cb91bb531ee75aa2c2cde26a01ceb5ff0a

java/com/google/gerrit/server/AnonymousUser.java

@@ -26,6 +26,12 @@ public class AnonymousUser extends CurrentUser {
     return new ListGroupMembership(Collections.singleton(SystemGroupBackend.ANONYMOUS_USERS));
   }
 
+  @Override
+  public Object getCacheKey() {
+    // Treat all anonymous users as a single user
+    return "anonymous";
+  }
+
   @Override
   public String toString() {
     return "ANONYMOUS";

java/com/google/gerrit/server/CurrentUser.java

@@ -90,6 +90,12 @@ public abstract class CurrentUser {
    */
   public abstract GroupMembership getEffectiveGroups();
 
+  /**
+   * Returns a unique identifier for this user that is intended to be used as a cache key. Returned
+   * object should to implement {@code equals()} and {@code hashCode()} for effective caching.
+   */
+  public abstract Object getCacheKey();
+
   /** Unique name of the user on this server, if one has been assigned. */
   public Optional<String> getUserName() {
     return Optional.empty();

java/com/google/gerrit/server/IdentifiedUser.java

@@ -390,6 +390,11 @@ public class IdentifiedUser extends CurrentUser {
     return effectiveGroups;
   }
 
+  @Override
+  public Object getCacheKey() {
+    return getAccountId();
+  }
+
   public PersonIdent newRefLogIdent() {
     return newRefLogIdent(new Date(), TimeZone.getDefault());
   }

java/com/google/gerrit/server/InternalUser.java

@@ -35,6 +35,11 @@ public class InternalUser extends CurrentUser {
     return GroupMembership.EMPTY;
   }
 
+  @Override
+  public String getCacheKey() {
+    return "internal";
+  }
+
   @Override
   public boolean isInternalUser() {
     return true;

java/com/google/gerrit/server/PeerDaemonUser.java

@@ -40,6 +40,11 @@ public class PeerDaemonUser extends CurrentUser {
     return GroupMembership.EMPTY;
   }
 
+  @Override
+  public Object getCacheKey() {
+    return getRemoteAddress();
+  }
+
   public SocketAddress getRemoteAddress() {
     return peer;
   }

java/com/google/gerrit/server/query/change/SingleGroupUser.java

@@ -36,4 +36,9 @@ public final class SingleGroupUser extends CurrentUser {
   public GroupMembership getEffectiveGroups() {
     return groups;
   }
+
+  @Override
+  public Object getCacheKey() {
+    return groups.getKnownGroups();
+  }
 }