MDEV-8931: (server part of) session state tracking

initial commit to test

sql/session_tracker.h

@@ -0,0 +1,159 @@
+#ifndef SESSION_TRACKER_INCLUDED
+#define SESSION_TRACKER_INCLUDED
+
+/* Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+   Copyright (c) 2016, MariaDB
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
+
+#include "m_string.h"
+#include "thr_lock.h"
+
+/* forward declarations */
+class THD;
+class set_var;
+class String;
+
+
+enum enum_session_tracker
+{
+  SESSION_SYSVARS_TRACKER,                       /* Session system variables */
+  CURRENT_SCHEMA_TRACKER,                        /* Current schema */
+  SESSION_STATE_CHANGE_TRACKER,
+  SESSION_GTIDS_TRACKER,                         /* Tracks GTIDs */
+  TRANSACTION_INFO_TRACKER                       /* Transaction state */
+};
+
+#define SESSION_TRACKER_END TRANSACTION_INFO_TRACKER
+
+
+/**
+  State_tracker
+
+  An abstract class that defines the interface for any of the server's
+  'session state change tracker'. A tracker, however, is a sub- class of
+  this class which takes care of tracking the change in value of a part-
+  icular session state type and thus defines various methods listed in this
+  interface. The change information is later serialized and transmitted to
+  the client through protocol's OK packet.
+
+  Tracker system variables :-
+  A tracker is normally mapped to a system variable. So in order to enable,
+  disable or modify the sub-entities of a tracker, the user needs to modify
+  the respective system variable either through SET command or via command
+  line option. As required in system variable handling, this interface also
+  includes two functions to help in the verification of the supplied value
+  (ON_CHECK) and the updation (ON_UPDATE) of the tracker system variable,
+  namely - check() and update().
+*/
+
+class State_tracker
+{
+protected:
+  /**
+    Is tracking enabled for a particular session state type ?
+
+    @note: It is cache to avoid virtual functions and checking thd
+    when we want mark tracker as changed.
+  */
+  bool m_enabled;
+
+  /** Has the session state type changed ? */
+  bool m_changed;
+
+public:
+  /** Constructor */
+  State_tracker() : m_enabled(false), m_changed(false)
+  {}
+
+  /** Destructor */
+  virtual ~State_tracker()
+  {}
+
+  /** Getters */
+  bool is_enabled() const
+  { return m_enabled; }
+
+  bool is_changed() const
+  { return m_changed; }
+
+  /** Called in the constructor of THD*/
+  virtual bool enable(THD *thd)= 0;
+
+  /** To be invoked when the tracker's system variable is checked (ON_CHECK). */
+  virtual bool check(THD *thd, set_var *var)= 0;
+
+  /** To be invoked when the tracker's system variable is updated (ON_UPDATE).*/
+  virtual bool update(THD *thd)= 0;
+
+  /** Store changed data into the given buffer. */
+  virtual bool store(THD *thd, String *buf)= 0;
+
+  /** Mark the entity as changed. */
+  virtual void mark_as_changed(THD *thd, LEX_CSTRING *name)= 0;
+};
+
+
+/**
+  Session_tracker
+
+  This class holds an object each for all tracker classes and provides
+  methods necessary for systematic detection and generation of session
+  state change information.
+*/
+
+class Session_tracker
+{
+private:
+  State_tracker *m_trackers[SESSION_TRACKER_END + 1];
+
+  /* The following two functions are private to disable copying. */
+  Session_tracker(Session_tracker const &other)
+  {
+    DBUG_ASSERT(FALSE);
+  }
+  Session_tracker& operator= (Session_tracker const &rhs)
+  {
+    DBUG_ASSERT(FALSE);
+    return *this;
+  }
+
+public:
+
+  Session_tracker();
+  ~Session_tracker()
+  {
+    for (int i= 0; i <= SESSION_TRACKER_END; i ++)
+      delete m_trackers[i];
+  }
+  void enable(THD *thd);
+
+  /** Returns the pointer to the tracker object for the specified tracker. */
+  inline State_tracker *get_tracker(enum_session_tracker tracker) const
+  {
+    return m_trackers[tracker];
+  }
+
+  inline void mark_as_changed(THD *thd, enum enum_session_tracker tracker,
+                              LEX_CSTRING *data)
+  {
+    if (m_trackers[tracker]->is_enabled())
+      m_trackers[tracker]->mark_as_changed(thd, data);
+  }
+
+
+  void store(THD *thd, String *main_buf);
+};
+
+#endif /* SESSION_TRACKER_INCLUDED */