Thank you dslake for diagnosing and fixing a race condition in OGS1SecureInventoryServer (mantis #3483). The provided patch was slightly modified to narrow the locking scope to smaller portions of the functions. Applied the same locking to HGInventoryService, which suffered from the same race condition.

OpenSim/Region/Communications/Hypergrid/HGInventoryService.cs

@@ -77,10 +77,18 @@ namespace OpenSim.Region.Communications.Hypergrid
             }
 
             // grid/hypergrid mode
+            lock (m_RequestingInventory)
+            {
                 if (!m_RequestingInventory.ContainsKey(userID))
                 {
                     m_RequestingInventory.Add(userID, callback);
-
+                }
+                else
+                {
+                    m_log.ErrorFormat("[HGrid INVENTORY SERVICE]: RequestInventoryForUser() - could  not find user profile for {0}", userID);
+                    return;
+                }
+            }
             string invServer = GetUserInventoryURI(userID);
             m_log.InfoFormat(
                 "[HGrid INVENTORY SERVICE]: Requesting inventory from {0}/GetInventory/ for user {1} ({2})",
@@ -118,12 +126,6 @@ namespace OpenSim.Region.Communications.Hypergrid
                 InventoryResponse(icol);
             }            
         }
-            else
-            {
-                m_log.ErrorFormat("[HGrid INVENTORY SERVICE]: RequestInventoryForUser() - could  not find user profile for {0}", userID);
-            }
-            
-        }
 
         private delegate InventoryCollection GetInventoryDelegate(string url, UUID userID, UUID sessionID);
 
@@ -447,14 +449,28 @@ namespace OpenSim.Region.Communications.Hypergrid
         private void InventoryResponse(InventoryCollection response)
         {
             UUID userID = response.UserID;
+            InventoryReceiptCallback callback = null;
+            lock (m_RequestingInventory)
+            {
                 if (m_RequestingInventory.ContainsKey(userID))
                 {
                     m_log.InfoFormat("[HGrid INVENTORY SERVICE]: " +
                                      "Received inventory response for user {0} containing {1} folders and {2} items",
                                      userID, response.Folders.Count, response.Items.Count);
+                    callback = m_RequestingInventory[userID];
+                    m_RequestingInventory.Remove(userID);
+                }
+                else
+                {
+                    m_log.WarnFormat(
+                        "[HGrid INVENTORY SERVICE]: " +
+                        "Received inventory response for {0} for which we do not have a record of requesting!",
+                        userID);
+                    return;
+                }
+            }
 
             InventoryFolderImpl rootFolder = null;
-                InventoryReceiptCallback callback = m_RequestingInventory[userID];
 
             ICollection<InventoryFolderImpl> folders = new List<InventoryFolderImpl>();
             ICollection<InventoryItemBase> items = new List<InventoryItemBase>();
@@ -490,19 +506,9 @@ namespace OpenSim.Region.Communications.Hypergrid
                 m_log.ErrorFormat("[HGrid INVENTORY SERVICE]: Did not get back an inventory containing a root folder for user {0}", userID);
             }
 
-                m_RequestingInventory.Remove(userID);
             callback(folders, items);
 
         }
-            else
-            {
-                m_log.WarnFormat(
-                    "[HGrid INVENTORY SERVICE]: " +
-                    "Received inventory response for {0} for which we do not have a record of requesting!",
-                    userID);
-            }
-        }
-
 
         private bool IsLocalStandaloneUser(UUID userID)
         {

OpenSim/Region/Communications/OGS1/OGS1SecureInventoryService.cs

@@ -69,9 +69,16 @@ namespace OpenSim.Region.Communications.OGS1
         /// <param name="callback"></param>
         public void RequestInventoryForUser(UUID userID, UUID session_id, InventoryReceiptCallback callback)
         {
-            if (!m_RequestingInventory.ContainsKey(userID))
+            lock (m_RequestingInventory)
             {
+                if (!m_RequestingInventory.ContainsKey(userID))
                     m_RequestingInventory.Add(userID, callback);
+                else
+                {
+                    m_log.ErrorFormat("[OGS1 INVENTORY SERVICE]: RequestInventoryForUser() - could you not find user profile for {0}", userID);
+                    return;
+                }
+            }
 
             try
             {
@@ -94,11 +101,6 @@ namespace OpenSim.Region.Communications.OGS1
                     e.Source, e.Message);
             }
         }
-            else
-            {
-                m_log.ErrorFormat("[OGS1 INVENTORY SERVICE]: RequestInventoryForUser() - could you not find user profile for {0}", userID);
-            }
-        }
 
         /// <summary>
         /// Callback used by the inventory server GetInventory request
@@ -107,14 +109,29 @@ namespace OpenSim.Region.Communications.OGS1
         private void InventoryResponse(InventoryCollection response)
         {
             UUID userID = response.UserID;
+            InventoryReceiptCallback callback = null;
+            lock (m_RequestingInventory)
+            {
                 if (m_RequestingInventory.ContainsKey(userID))
                 {
+                    callback = m_RequestingInventory[userID];
+                    m_RequestingInventory.Remove(userID);
+                }
+                else
+                {
+                    m_log.WarnFormat(
+                        "[OGS1 INVENTORY SERVICE]: " +
+                        "Received inventory response for {0} for which we do not have a record of requesting!",
+                        userID);
+                    return;
+                }
+            }
+
             m_log.InfoFormat("[OGS1 INVENTORY SERVICE]: " +
                              "Received inventory response for user {0} containing {1} folders and {2} items",
                              userID, response.Folders.Count, response.Items.Count);
 
             InventoryFolderImpl rootFolder = null;
-                InventoryReceiptCallback callback = m_RequestingInventory[userID];
 
             ICollection<InventoryFolderImpl> folders = new List<InventoryFolderImpl>();
             ICollection<InventoryItemBase> items = new List<InventoryItemBase>();
@@ -152,15 +169,6 @@ namespace OpenSim.Region.Communications.OGS1
 
             callback(folders, items);
 
-                m_RequestingInventory.Remove(userID);
-            }
-            else
-            {
-                m_log.WarnFormat(
-                    "[OGS1 INVENTORY SERVICE]: " +
-                    "Received inventory response for {0} for which we do not have a record of requesting!",
-                    userID);
-            }
         }
 
         /// <summary>