cleanup: string sys_var types

Merge sys_var_charptr with sys_var_charptr_base, as well as merge
Sys_var_session_lexstring into Sys_var_lexstring. Also refactored
update methods of sys_var_charptr accordingly.

Because the class is more generic, session_update() calls
sys_var_charptr::session_update() which does not assume a buffer field
associated with THD, but instead call strdup/free, we get rid of
THD::default_master_connection_buff accordingly. This also makes THD
smaller by ~192 bytes, and there can be many thousands of concurrent
THDs.

mysql-test/suite/sys_vars/r/mdev_15935.result

+#
+# test cleanup of sys_var classes
+#
+set global init_connect=".................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................";
+ERROR HY000: String '......................................................................' is too long for init_connect (should be no longer than 2000)
+set global ft_boolean_syntax=".................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................";
+ERROR HY000: String '......................................................................' is too long for ft_boolean_syntax (should be no longer than 2000)
+#
+# end of test mdev_15935
+#

mysql-test/suite/sys_vars/t/mdev_15935.test

+--echo #
+--echo # test cleanup of sys_var classes
+--echo #
+
+--let $long_string=`select repeat('.', 2001)`
+--error ER_WRONG_STRING_LENGTH
+eval set global init_connect="$long_string";
+--error ER_WRONG_STRING_LENGTH
+eval set global ft_boolean_syntax="$long_string";
+
+--echo #
+--echo # end of test mdev_15935
+--echo #

sql/sql_class.cc

@@ -1235,10 +1235,7 @@ void THD::init()
     avoid temporary tables replication failure.
   */
   variables.pseudo_thread_id= thread_id;
-  variables.default_master_connection.str= default_master_connection_buff;
-  ::strmake(default_master_connection_buff,
-            global_system_variables.default_master_connection.str,
-            variables.default_master_connection.length);
+
   mysql_mutex_unlock(&LOCK_global_system_variables);
 
   user_time.val= start_time= start_time_sec_part= 0;

sql/sql_class.h

@@ -3750,7 +3750,6 @@ class THD: public THD_count, /* this must be first */
     This is used for taging error messages in the log files.
   */
   LEX_CSTRING connection_name;
-  char       default_master_connection_buff[MAX_CONNECTION_NAME+1];
   uint8      password; /* 0, 1 or 2 */
   uint8      failed_com_change_user;
   bool       slave_thread;

sql/sql_plugin.cc

@@ -3279,6 +3279,9 @@ void plugin_thdvar_init(THD *thd)
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.deinit(thd);
 #endif
+  my_free((char*) thd->variables.default_master_connection.str);
+  thd->variables.default_master_connection.str= 0;
+  thd->variables.default_master_connection.length= 0;
 
   thd->variables= global_system_variables;
 
@@ -3301,6 +3304,11 @@ void plugin_thdvar_init(THD *thd)
   intern_plugin_unlock(NULL, old_enforced_table_plugin);
   mysql_mutex_unlock(&LOCK_plugin);
 
+  thd->variables.default_master_connection.str=
+    my_strndup(key_memory_Sys_var_charptr_value,
+               global_system_variables.default_master_connection.str,
+               global_system_variables.default_master_connection.length,
+               MYF(MY_WME | MY_THREAD_SPECIFIC));
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.init(thd);
 #endif
@@ -3372,6 +3380,9 @@ void plugin_thdvar_cleanup(THD *thd)
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.deinit(thd);
 #endif
+  my_free((char*) thd->variables.default_master_connection.str);
+  thd->variables.default_master_connection.str= 0;
+  thd->variables.default_master_connection.length= 0;
 
   mysql_mutex_lock(&LOCK_plugin);
 

sql/sys_vars.cc

@@ -1346,12 +1346,11 @@ static bool check_master_connection(sys_var *self, THD *thd, set_var *var)
   return false;
 }
 
-static Sys_var_session_lexstring Sys_default_master_connection(
+static Sys_var_lexstring Sys_default_master_connection(
        "default_master_connection",
        "Master connection to use for all slave variables and slave commands",
-       SESSION_ONLY(default_master_connection),
-       NO_CMD_LINE,
-       DEFAULT(""), MAX_CONNECTION_NAME, ON_CHECK(check_master_connection));
+       SESSION_ONLY(default_master_connection), NO_CMD_LINE, DEFAULT(""),
+       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_master_connection));
 #endif
 
 static Sys_var_charptr_fscs Sys_init_file(

sql/sys_vars.inl

@@ -492,14 +492,18 @@ class Sys_var_mybool: public Sys_var_typelib
   Backing store: char*
 
   @note
-  This class supports only GLOBAL variables, because THD on destruction
-  does not destroy individual members of SV, there's no way to free
-  allocated string variables for every thread.
+
+  Note that the memory management for SESSION_VAR's is manual, the
+  value must be strdup'ed in THD::init() and freed in
+  plugin_thdvar_cleanup(). TODO: it should be done automatically when
+  we'll have more session string variables to justify it. Maybe some
+  kind of a loop over all variables, like sys_var_end() in set_var.cc?
 */
-class Sys_var_charptr_base: public sys_var
+class Sys_var_charptr: public sys_var
 {
+  const size_t max_length= 2000;
 public:
-  Sys_var_charptr_base(const char *name_arg,
+  Sys_var_charptr(const char *name_arg,
           const char *comment, int flag_args, ptrdiff_t off, size_t size,
           CMD_LINE getopt,
           const char *def_val, PolyLock *lock=0,
@@ -519,8 +523,9 @@ class Sys_var_charptr_base: public sys_var
     */
     option.var_type|= (flags & ALLOCATED) ? GET_STR_ALLOC : GET_STR;
     global_var(const char*)= def_val;
+    SYSVAR_ASSERT(size == sizeof(char *));
   }
-  void cleanup()
+  void cleanup() override
   {
     if (flags & ALLOCATED)
     {
@@ -558,17 +563,26 @@ class Sys_var_charptr_base: public sys_var
 
     return false;
   }
-  bool do_check(THD *thd, set_var *var)
-  { return do_string_check(thd, var, charset(thd)); }
-  bool session_update(THD *thd, set_var *var)= 0;
-  char *global_update_prepare(THD *thd, set_var *var)
+  bool do_check(THD *thd, set_var *var) override
+  {
+    if (do_string_check(thd, var, charset(thd)))
+      return true;
+    if (var->save_result.string_value.length > max_length)
+    {
+      my_error(ER_WRONG_STRING_LENGTH, MYF(0), var->save_result.string_value.str,
+               name.str, (int) max_length);
+      return true;
+    }
+    return false;
+  }
+  char *update_prepare(set_var *var, myf my_flags)
   {
     char *new_val, *ptr= var->save_result.string_value.str;
     size_t len=var->save_result.string_value.length;
     if (ptr)
     {
       new_val= (char*)my_memdup(key_memory_Sys_var_charptr_value,
-                                ptr, len+1, MYF(MY_WME));
+                                ptr, len+1, my_flags);
       if (!new_val) return 0;
       new_val[len]=0;
     }
@@ -576,6 +590,13 @@ class Sys_var_charptr_base: public sys_var
       new_val= 0;
     return new_val;
   }
+  bool session_update(THD *thd, set_var *var) override
+  {
+    char *new_val= update_prepare(var, MYF(MY_WME | MY_THREAD_SPECIFIC));
+    my_free(session_var(thd, char*));
+    session_var(thd, char*)= new_val;
+    return (new_val == 0 && var->save_result.string_value.str != 0);
+  }
   void global_update_finish(char *new_val)
   {
     if (flags & ALLOCATED)
@@ -583,14 +604,19 @@ class Sys_var_charptr_base: public sys_var
     flags|= ALLOCATED;
     global_var(char*)= new_val;
   }
-  bool global_update(THD *thd, set_var *var)
+  bool global_update(THD *thd, set_var *var) override
   {
-    char *new_val= global_update_prepare(thd, var);
+    char *new_val= update_prepare(var, MYF(MY_WME));
     global_update_finish(new_val);
     return (new_val == 0 && var->save_result.string_value.str != 0);
   }
-  void session_save_default(THD *thd, set_var *var)= 0;
-  void global_save_default(THD *thd, set_var *var)
+  void session_save_default(THD *, set_var *var) override
+  {
+    var->save_result.string_value.str= global_var(char*);
+    var->save_result.string_value.length=
+      strlen(var->save_result.string_value.str);
+  }
+  void global_save_default(THD *, set_var *var) override
   {
     char *ptr= (char*)(intptr)option.def_value;
     var->save_result.string_value.str= ptr;
@@ -598,35 +624,6 @@ class Sys_var_charptr_base: public sys_var
   }
 };
 
-class Sys_var_charptr: public Sys_var_charptr_base
-{
-public:
-  Sys_var_charptr(const char *name_arg,
-          const char *comment, int flag_args, ptrdiff_t off, size_t size,
-          CMD_LINE getopt,
-          const char *def_val, PolyLock *lock=0,
-          enum binlog_status_enum binlog_status_arg=VARIABLE_NOT_IN_BINLOG,
-          on_check_function on_check_func=0,
-          on_update_function on_update_func=0,
-          const char *substitute=0) :
-    Sys_var_charptr_base(name_arg, comment, flag_args, off, size, getopt,
-                         def_val, lock, binlog_status_arg,
-                         on_check_func, on_update_func, substitute)
-  {
-    SYSVAR_ASSERT(scope() == GLOBAL);
-    SYSVAR_ASSERT(size == sizeof(char *));
-  }
-
-  bool session_update(THD *thd, set_var *var)
-  {
-    DBUG_ASSERT(FALSE);
-    return true;
-  }
-  void session_save_default(THD *thd, set_var *var)
-  { DBUG_ASSERT(FALSE); }
-};
-
-
 class Sys_var_charptr_fscs: public Sys_var_charptr
 {
   using Sys_var_charptr::Sys_var_charptr;
@@ -637,23 +634,22 @@ class Sys_var_charptr_fscs: public Sys_var_charptr
   }
 };
 
-
 #ifndef EMBEDDED_LIBRARY
-class Sys_var_sesvartrack: public Sys_var_charptr_base
+class Sys_var_sesvartrack: public Sys_var_charptr
 {
 public:
   Sys_var_sesvartrack(const char *name_arg,
                       const char *comment,
                       CMD_LINE getopt,
                       const char *def_val, PolyLock *lock= 0) :
-    Sys_var_charptr_base(name_arg, comment,
+    Sys_var_charptr(name_arg, comment,
                     SESSION_VAR(session_track_system_variables),
                     getopt, def_val, lock,
                     VARIABLE_NOT_IN_BINLOG, 0, 0, 0)
     {}
   bool do_check(THD *thd, set_var *var)
   {
-     if (Sys_var_charptr_base::do_check(thd, var) ||
+     if (Sys_var_charptr::do_string_check(thd, var, charset(thd)) ||
          sysvartrack_validate_value(thd, var->save_result.string_value.str,
                                     var->save_result.string_value.length))
        return TRUE;
@@ -661,7 +657,7 @@ class Sys_var_sesvartrack: public Sys_var_charptr_base
   }
   bool global_update(THD *thd, set_var *var)
   {
-    char *new_val= global_update_prepare(thd, var);
+    char *new_val= update_prepare(var, MYF(MY_WME));
     if (new_val)
     {
       if (sysvartrack_global_update(thd, new_val,
@@ -858,7 +854,19 @@ class Sys_var_binlog_filter: public sys_var
   Backing store: LEX_CSTRING
 
   @note
-  Behaves exactly as Sys_var_charptr, only the backing store is different.
+  Behaves exactly as Sys_var_charptr, only the backing store is
+  different.
+
+  Note that for global variables handle_options() only sets the
+  pointer, whereas the length must be updated manually to match, which
+  is done in mysqld.cc. See e.g. opt_init_connect. TODO: it should be
+  done automatically when we'll have more Sys_var_lexstring variables
+  to justify it. Maybe some kind of a loop over all variables, like
+  sys_var_end() in set_var.cc?
+
+  Note that as a subclass of Sys_var_charptr, the memory management
+  for session Sys_var_lexstring's is manual too, see notes of
+  Sys_var_charptr and for example default_master_connection.
 */
 class Sys_var_lexstring: public Sys_var_charptr
 {
@@ -886,88 +894,15 @@ class Sys_var_lexstring: public Sys_var_charptr
     global_var(LEX_CSTRING).length= var->save_result.string_value.length;
     return false;
   }
-};
-
-
-/*
-  A LEX_CSTRING stored only in thd->variables
-  Only to be used for small buffers
-*/
-
-class Sys_var_session_lexstring: public sys_var
-{
-  size_t max_length;
-public:
-  Sys_var_session_lexstring(const char *name_arg,
-                            const char *comment, int flag_args,
-                            ptrdiff_t off, size_t size, CMD_LINE getopt,
-                            const char *def_val, size_t max_length_arg,
-                            on_check_function on_check_func=0,
-                            on_update_function on_update_func=0)
-    : sys_var(&all_sys_vars, name_arg, comment, flag_args, off, getopt.id,
-              getopt.arg_type, SHOW_CHAR, (intptr)def_val,
-              0, VARIABLE_NOT_IN_BINLOG, on_check_func, on_update_func,
-              0),max_length(max_length_arg)
-  {
-    option.var_type|= GET_STR;
-    SYSVAR_ASSERT(scope() == ONLY_SESSION)
-    *const_cast<SHOW_TYPE*>(&show_val_type)= SHOW_LEX_STRING;
-  }
-  bool do_check(THD *thd, set_var *var)
-  {
-    char buff[STRING_BUFFER_USUAL_SIZE];
-    String str(buff, sizeof(buff), system_charset_info), *res;
-
-    if (!(res=var->value->val_str(&str)))
-    {
-      var->save_result.string_value.str= 0;     /* NULL */
-      var->save_result.string_value.length= 0;
-    }
-    else
-    {
-      if (res->length() > max_length)
-      {
-        my_error(ER_WRONG_STRING_LENGTH, MYF(0),
-                 res->ptr(), name.str, (int) max_length);
-        return true;
-      }
-      var->save_result.string_value.str= thd->strmake(res->ptr(),
-                                                      res->length());
-      var->save_result.string_value.length= res->length();
-    }
-    return false;
-  }
   bool session_update(THD *thd, set_var *var)
   {
-    LEX_CSTRING *tmp= &session_var(thd, LEX_CSTRING);
-    tmp->length= var->save_result.string_value.length;
-    /* Store as \0 terminated string (just to be safe) */
-    strmake((char*) tmp->str, var->save_result.string_value.str, tmp->length);
-    return false;
-  }
-  bool global_update(THD *thd, set_var *var)
-  {
-    DBUG_ASSERT(FALSE);
+    if (Sys_var_charptr::session_update(thd, var))
+      return true;
+    session_var(thd, LEX_CSTRING).length= var->save_result.string_value.length;
     return false;
   }
-  void session_save_default(THD *thd, set_var *var)
-  {
-    char *ptr= (char*)(intptr)option.def_value;
-    var->save_result.string_value.str= ptr;
-    var->save_result.string_value.length= strlen(ptr);
-  }
-  void global_save_default(THD *thd, set_var *var)
-  {
-    DBUG_ASSERT(FALSE);
-  }
-  const uchar *global_value_ptr(THD *thd, const LEX_CSTRING *base) const
-  {
-    DBUG_ASSERT(FALSE);
-    return NULL;
-  }
 };
 
-
 #ifndef DBUG_OFF
 /**
   @@session.debug_dbug and @@global.debug_dbug variables.