Change session registry to a template class

The template class wraps a HashMap such that only a few operations
are allowed. Usage requires specializing a RegistryTraits class
template for each entry type.

server/core/maxscale/session.hh

@@ -0,0 +1,39 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cppdefs.hh>
+#include <maxscale/session.h>
+
+namespace maxscale
+{
+/**
+ * Specialization of RegistryTraits for the session registry.
+ */
+template<>
+struct RegistryTraits<MXS_SESSION>
+{
+    typedef uint64_t id_type;
+    typedef MXS_SESSION* entry_type;
+
+    static id_type get_id(entry_type entry)
+    {
+        return entry->ses_id;
+    }
+    static entry_type null_entry()
+    {
+        return NULL;
+    }
+};
+
+}

server/core/maxscale/worker.hh

@@ -14,13 +14,14 @@
 
 #include <maxscale/cppdefs.hh>
 #include <memory>
-#include <tr1/unordered_map>
 #include <maxscale/platform.h>
 #include <maxscale/session.h>
+#include <maxscale/utils.hh>
 #include "messagequeue.hh"
 #include "poll.h"
 #include "worker.h"
 #include "workertask.hh"
+#include "session.hh"
 
 namespace maxscale
 {
@@ -69,7 +70,7 @@ public:
     typedef WORKER_STATISTICS STATISTICS;
     typedef WorkerTask Task;
     typedef WorkerDisposableTask DisposableTask;
-    typedef std::tr1::unordered_map<uint64_t, MXS_SESSION*> SessionsById;
+    typedef Registry<MXS_SESSION> SessionsById;
 
     enum state_t
     {
@@ -397,28 +398,11 @@ public:
     bool post_message(uint32_t msg_id, intptr_t arg1, intptr_t arg2);
 
     /**
-     * Add a session to the session container.
+     * Return a reference to the session registry of this worker.
      *
-     * @param session The session to add
-     * @return true if successful
+     * @return Session registry.
      */
-    bool register_session(MXS_SESSION* session);
-
-    /**
-     * Remove a session from the session container.
-     *
-     * @param id Session id
-     * @return The removed session, or NULL if not found
-     */
-    MXS_SESSION* deregister_session(uint64_t id);
-
-    /**
-     * Find a session in the session container.
-     *
-     * @param id Session id
-     * @return The found session, or NULL if not found
-     */
-    MXS_SESSION* find_session(uint64_t id);
+    SessionsById& session_registry();
 
     /**
      * Broadcast a message to all worker.