MXS-553: Provide full session to DCB mapping

By storing a link to the backend DCBs in the session object itself, we can
reach all related objects from the session. This removes the need to
iterate over all DCBs to find the set of related DCBs.

include/maxscale/session.h

@@ -29,12 +29,15 @@
 
 #ifdef __cplusplus
 #include <tr1/unordered_map>
+#include <tr1/unordered_set>
 #include <string>
 #include <deque>
 #include <vector>
 typedef std::deque<std::vector<uint8_t> > SessionStmtQueue;
+typedef std::tr1::unordered_set<DCB*> DCBSet;
 #else
 typedef void SessionStmtQueue;
+typedef void DCBSet;
 #endif
 
 MXS_BEGIN_DECLS
@@ -211,6 +214,7 @@ typedef struct session
         GWBUF* buffer;   /*< Buffer to deliver to up. */
     } response;                               /*< Shortcircuited response */
     SessionStmtQueue*      last_statements;   /*< The N last statements by the client */
+    DCBSet*                dcb_set;           /*< Set of associated backend DCBs */
     skygw_chk_t     ses_chk_tail;
 } MXS_SESSION;
 

server/core/dcb.cc

@@ -245,7 +245,7 @@ dcb_final_free(DCB *dcb)
                                   DCB_ROLE_SERVICE_LISTENER == dcb->dcb_role ||
                                   DCB_ROLE_INTERNAL == dcb->dcb_role);
 
-            session_put_ref(local_session);
+            session_unlink_backend_dcb(local_session, dcb);
 
             if (is_client_dcb)
             {
@@ -464,7 +464,7 @@ dcb_connect(SERVER *server, MXS_SESSION *session, const char *protocol)
         MXS_DEBUG("Failed to connect to server [%s]:%d, from backend dcb %p, client dcp %p fd %d",
                   server->address, server->port, dcb, session->client_dcb, session->client_dcb->fd);
         // Remove the inc ref that was done in session_link_backend_dcb().
-        session_put_ref(dcb->session);
+        session_unlink_backend_dcb(dcb->session, dcb);
         dcb->session = NULL;
         dcb_free_all_memory(dcb);
         return NULL;
@@ -501,7 +501,7 @@ dcb_connect(SERVER *server, MXS_SESSION *session, const char *protocol)
         close(dcb->fd);
         dcb->fd = DCBFD_CLOSED;
         // Remove the inc ref that was done in session_link_backend_dcb().
-        session_put_ref(dcb->session);
+        session_unlink_backend_dcb(dcb->session, dcb);
         dcb->session = NULL;
         dcb_free_all_memory(dcb);
         return NULL;
@@ -517,7 +517,7 @@ dcb_connect(SERVER *server, MXS_SESSION *session, const char *protocol)
         close(dcb->fd);
         dcb->fd = DCBFD_CLOSED;
         // Remove the inc ref that was done in session_link_backend_dcb().
-        session_put_ref(dcb->session);
+        session_unlink_backend_dcb(dcb->session, dcb);
         dcb->session = NULL;
         dcb_free_all_memory(dcb);
         return NULL;
@@ -1326,7 +1326,7 @@ dcb_maybe_add_persistent(DCB *dcb)
             CHK_SESSION(local_session);
             if (SESSION_STATE_DUMMY != local_session->state)
             {
-                session_put_ref(local_session);
+                session_unlink_backend_dcb(local_session, dcb);
             }
         }
 

server/core/internal/session.h

@@ -51,6 +51,14 @@ const char *session_state(mxs_session_state_t);
  */
 void session_link_backend_dcb(MXS_SESSION *session, struct dcb *dcb);
 
+/**
+ * Unlink a session to a backend DCB.
+ *
+ * @param session  The session to unlink with the dcb
+ * @param dcb      The backend DCB to be unlinked
+ */
+void session_unlink_backend_dcb(MXS_SESSION *session, struct dcb *dcb);
+
 RESULTSET *sessionGetList(SESSIONLISTFILTER);
 
 void printAllSessions();

server/core/session.cc

@@ -106,17 +106,19 @@ MXS_SESSION* session_alloc_with_id(SERVICE *service, DCB *client_dcb, uint64_t i
 {
     MXS_SESSION *session = (MXS_SESSION *)(MXS_MALLOC(sizeof(*session)));
     SessionVarsByName *session_variables = new (std::nothrow) SessionVarsByName;
+    DCBSet* dcb_set = new (std::nothrow) DCBSet;
 
-    if ((session == NULL) || (session_variables == NULL))
+    if ((session == NULL) || (session_variables == NULL) || (dcb_set == NULL))
     {
         MXS_FREE(session);
         delete session_variables;
-
+        delete dcb_set;
         return NULL;
     }
 
     session_initialize(session);
     session->variables = session_variables;
+    session->dcb_set = dcb_set;
     session->ses_id = id;
     return session_alloc_body(service, client_dcb, session);
 }
@@ -279,6 +281,13 @@ void session_link_backend_dcb(MXS_SESSION *session, DCB *dcb)
     dcb->service = session->service;
     /** Move this DCB under the same thread */
     dcb->poll.thread.id = session->client_dcb->poll.thread.id;
+    session->dcb_set->insert(dcb);
+}
+
+void session_unlink_backend_dcb(MXS_SESSION *session, DCB *dcb)
+{
+    session->dcb_set->erase(dcb);
+    session_put_ref(session);
 }
 
 /**
@@ -396,6 +405,7 @@ session_final_free(MXS_SESSION *session)
 
     delete session->variables;
     delete session->last_statements;
+    delete session->dcb_set;
     MXS_FREE(session);
 }
 

server/modules/filter/test/mock_session.cc

@@ -45,6 +45,8 @@ Session::Session(Client* pClient)
 Session::~Session()
 {
     delete variables;
+    delete last_statements;
+    delete dcb_set;
 }
 
 Client& Session::client() const