Add experimental [Groups] MessageOnlineUsersOnly option for Flotsam XmlRpc groups.

This retrieves and caches information from the PresenceService to only send messages to online users.
This is reported to much improve performance for large groups where most users are offline.
Cache is 20 seconds to balance requests against users not receiving messages until cache updates.
This is an alternative to an approach where login/logout notification is sent directly from simulator to groups service.
However, I'm not convinced that this PresenceService approach is actually better.  Needs more thought.

OpenSim/Region/OptionalModules/Avatar/XmlRpcGroups/GroupsMessagingModule.cs

@@ -27,6 +27,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Reflection;
 using log4net;
 using Mono.Addins;
@@ -36,6 +37,8 @@ using OpenMetaverse.StructuredData;
 using OpenSim.Framework;
 using OpenSim.Region.Framework.Interfaces;
 using OpenSim.Region.Framework.Scenes;
+using OpenSim.Services.Interfaces;
+using PresenceInfo = OpenSim.Services.Interfaces.PresenceInfo;
 
 namespace OpenSim.Region.OptionalModules.Avatar.XmlRpcGroups
 {
@@ -45,6 +48,7 @@ namespace OpenSim.Region.OptionalModules.Avatar.XmlRpcGroups
         private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
 
         private List<Scene> m_sceneList = new List<Scene>();
+        private IPresenceService m_presenceService;
 
         private IMessageTransferModule m_msgTransferModule = null;
 
@@ -54,6 +58,27 @@ namespace OpenSim.Region.OptionalModules.Avatar.XmlRpcGroups
         private bool m_groupMessagingEnabled = false;
         private bool m_debugEnabled = true;
 
+        /// <summary>
+        /// If enabled, module only tries to send group IMs to online users by querying cached presence information.
+        /// </summary>
+        private bool m_messageOnlineAgentsOnly;
+
+        /// <summary>
+        /// Cache for online users.
+        /// </summary>
+        /// <remarks>
+        /// Group ID is key, presence information for online members is value.
+        /// Will only be non-null if m_messageOnlineAgentsOnly = true
+        /// We cache here so that group messages don't constantly have to re-request the online user list to avoid
+        /// attempted expensive sending of messages to offline users.
+        /// The tradeoff is that a user that comes online will not receive messages consistently from all other users
+        /// until caches have updated.
+        /// Therefore, we set the cache expiry to just 20 seconds.
+        /// </remarks>
+        private ExpiringCache<UUID, PresenceInfo[]> m_usersOnlineCache;
+
+        private int m_usersOnlineCacheExpirySeconds = 20;
+
         #region IRegionModuleBase Members
 
         public void Initialise(IConfigSource config)
@@ -83,10 +108,17 @@ namespace OpenSim.Region.OptionalModules.Avatar.XmlRpcGroups
                     return;
                 }
 
+                m_messageOnlineAgentsOnly = groupsConfig.GetBoolean("MessageOnlineUsersOnly", false);
+
+                if (m_messageOnlineAgentsOnly)
+                     m_usersOnlineCache = new ExpiringCache<UUID, PresenceInfo[]>();
+
                 m_debugEnabled = groupsConfig.GetBoolean("DebugEnabled", true);
             }
 
-            m_log.Info("[GROUPS-MESSAGING]: GroupsMessagingModule starting up");
+            m_log.InfoFormat(
+                "[GROUPS-MESSAGING]: GroupsMessagingModule enabled with MessageOnlineOnly = {0}, DebugEnabled = {1}",
+                m_messageOnlineAgentsOnly, m_debugEnabled);
         }
 
         public void AddRegion(Scene scene)
@@ -126,6 +158,8 @@ namespace OpenSim.Region.OptionalModules.Avatar.XmlRpcGroups
                 return;
             }
 
+            if (m_presenceService == null)
+                m_presenceService = scene.PresenceService;
 
             m_sceneList.Add(scene);
 
@@ -208,10 +242,38 @@ namespace OpenSim.Region.OptionalModules.Avatar.XmlRpcGroups
         {
             List<GroupMembersData> groupMembers = m_groupData.GetGroupMembers(new UUID(im.fromAgentID), groupID);
 
+            if (m_messageOnlineAgentsOnly)
+            {
+                string[] t1 = groupMembers.ConvertAll<string>(gmd => gmd.AgentID.ToString()).ToArray();
+
+                // We cache in order not to overwhlem the presence service on large grids with many groups.  This does
+                // mean that members coming online will not see all group members until after m_usersOnlineCacheExpirySeconds has elapsed.
+                // (assuming this is the same across all grid simulators).
+                PresenceInfo[] onlineAgents;
+                if (!m_usersOnlineCache.TryGetValue(groupID, out onlineAgents))
+                {
+                    onlineAgents = m_presenceService.GetAgents(t1);
+                    m_usersOnlineCache.Add(groupID, onlineAgents, m_usersOnlineCacheExpirySeconds);
+                }
+
+                HashSet<string> onlineAgentsUuidSet = new HashSet<string>();
+                Array.ForEach<PresenceInfo>(onlineAgents, pi => onlineAgentsUuidSet.Add(pi.UserID));
+
+                int allMembersCount = groupMembers.Count;
+                groupMembers = groupMembers.Where(gmd => onlineAgentsUuidSet.Contains(gmd.AgentID.ToString())).ToList();
+
+    //            if (m_debugEnabled)
+                    m_log.DebugFormat(
+                        "[GROUPS-MESSAGING]: SendMessageToGroup called for group {0} with {1} visible members, {2} online",
+                        groupID, allMembersCount, groupMembers.Count());
+            }
+            else
+            {
                 if (m_debugEnabled)
                     m_log.DebugFormat(
                         "[GROUPS-MESSAGING]: SendMessageToGroup called for group {0} with {1} visible members",
                         groupID, groupMembers.Count);
+            }
 
             foreach (GroupMembersData member in groupMembers)
             {

bin/OpenSimDefaults.ini

@@ -1577,6 +1577,11 @@
     MessagingModule = GroupsMessagingModule
     ;MessagingEnabled = true 
 
+    ; Experimental option to only message cached online users rather than all users
+    ; Should make large group with few online members messaging faster, as the expense of more calls to ROBUST presence service
+    ; This currently only applies to the Flotsam XmlRpc backend
+    MessageOnlineUsersOnly = false
+
     ; Service connectors to the Groups Service.  Select one depending on whether you're using a Flotsam XmlRpc backend or a SimianGrid backend
   
     ; SimianGrid Service for Groups