Bug#16194302: SUPPORT FOR FLOATING-POINT SYSTEM VARIABLES

              USING THE PLUGIN INTERFACE.

ISSUE: No support for floating-point plugin
       system variables.

SOLUTION: Allowing plugins to define and expose floating-point
          system variables of type double. MYSQL_SYSVAR_DOUBLE
          and MYSQL_THDVAR_DOUBLE are added.

ISSUE: Fractional part of the def, min, max values of system
       variables are ignored.

SOLUTION: Adding functions that are used to store the raw
          representation of a double in the raw bits of unsigned
          longlong in a way that the binary representation
          remains the same.

2 files changed, 66 insertions, 4 deletions

diff --git a/sql/sql_plugin.cc b/sql/sql_plugin.cc
index 13623078265..25dbf6a61f3 100644
--- a/sql/sql_plugin.cc
+++ b/sql/sql_plugin.cc
@@ -2059,6 +2059,7 @@ typedef DECLARE_MYSQL_SYSVAR_SIMPLE(sysvar_longlong_t, longlong);
 typedef DECLARE_MYSQL_SYSVAR_SIMPLE(sysvar_uint_t, uint);
 typedef DECLARE_MYSQL_SYSVAR_SIMPLE(sysvar_ulong_t, ulong);
 typedef DECLARE_MYSQL_SYSVAR_SIMPLE(sysvar_ulonglong_t, ulonglong);
+typedef DECLARE_MYSQL_SYSVAR_SIMPLE(sysvar_double_t, double);
 
 typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_int_t, int);
 typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_long_t, long);
@@ -2066,6 +2067,7 @@ typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_longlong_t, longlong);
 typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_uint_t, uint);
 typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_ulong_t, ulong);
 typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_ulonglong_t, ulonglong);
+typedef DECLARE_MYSQL_THDVAR_SIMPLE(thdvar_double_t, double);
 
 
 /****************************************************************************
@@ -2281,6 +2283,20 @@ err:
   return 1;
 }
 
+static int check_func_double(THD *thd, struct st_mysql_sys_var *var,
+                             void *save, st_mysql_value *value)
+{
+  double v;
+  my_bool fixed;
+  struct my_option option;
+
+  value->val_real(value, &v);
+  plugin_opt_set_limits(&option, var);
+  *(double *) save= getopt_double_limit_value(v, &option, &fixed);
+
+  return throw_bounds_warning(thd, var->name, fixed, v);
+}
+
 
 static void update_func_bool(THD *thd, struct st_mysql_sys_var *var,
                              void *tgt, const void *save)
@@ -2316,6 +2332,11 @@ static void update_func_str(THD *thd, struct st_mysql_sys_var *var,
   *(char **) tgt= *(char **) save;
 }
 
+static void update_func_double(THD *thd, struct st_mysql_sys_var *var,
+                               void *tgt, const void *save)
+{
+  *(double *) tgt= *(double *) save;
+}
 
 /****************************************************************************
   System Variables support
@@ -2430,6 +2451,9 @@ static st_bookmark *register_var(const char *plugin, const char *name,
   case PLUGIN_VAR_STR:
     size= sizeof(char*);
     break;
+  case PLUGIN_VAR_DOUBLE:
+    size= sizeof(double);
+    break;
   default:
     DBUG_ASSERT(0);
     return NULL;
@@ -2641,6 +2665,11 @@ static char **mysql_sys_var_str(THD* thd, int offset)
   return (char **) intern_sys_var_ptr(thd, offset, true);
 }
 
+static double *mysql_sys_var_double(THD* thd, int offset)
+{
+  return (double *) intern_sys_var_ptr(thd, offset, true);
+}
+
 void plugin_thdvar_init(THD *thd)
 {
   plugin_ref old_table_plugin= thd->variables.table_plugin;
@@ -2773,6 +2802,8 @@ static SHOW_TYPE pluginvar_show_type(st_mysql_sys_var *plugin_var)
   case PLUGIN_VAR_ENUM:
   case PLUGIN_VAR_SET:
     return SHOW_CHAR;
+  case PLUGIN_VAR_DOUBLE:
+    return SHOW_DOUBLE;
   default:
     DBUG_ASSERT(0);
     return SHOW_UNDEF;
@@ -2923,6 +2954,8 @@ bool sys_var_pluginvar::check_update_type(Item_result type)
   case PLUGIN_VAR_BOOL:
   case PLUGIN_VAR_SET:
     return type != STRING_RESULT && type != INT_RESULT;
+  case PLUGIN_VAR_DOUBLE:
+    return type != INT_RESULT && type != REAL_RESULT && type != DECIMAL_RESULT;
   default:
     return true;
   }
@@ -3048,6 +3081,9 @@ bool sys_var_pluginvar::global_update(THD *thd, set_var *var)
     case PLUGIN_VAR_STR:
       src= &((sysvar_str_t*) plugin_var)->def_val;
       break;
+    case PLUGIN_VAR_DOUBLE:
+      src= &((sysvar_double_t*) plugin_var)->def_val;
+      break;
     case PLUGIN_VAR_INT | PLUGIN_VAR_THDLOCAL:
       src= &((thdvar_uint_t*) plugin_var)->def_val;
       break;
@@ -3069,6 +3105,9 @@ bool sys_var_pluginvar::global_update(THD *thd, set_var *var)
     case PLUGIN_VAR_STR | PLUGIN_VAR_THDLOCAL:
       src= &((thdvar_str_t*) plugin_var)->def_val;
       break;
+    case PLUGIN_VAR_DOUBLE | PLUGIN_VAR_THDLOCAL:
+      src= &((thdvar_double_t*) plugin_var)->def_val;
+      break;
     default:
       DBUG_ASSERT(0);
     }
@@ -3092,6 +3131,13 @@ bool sys_var_pluginvar::global_update(THD *thd, set_var *var)
   options->max_value= (opt)->max_val; \
   options->block_size= (long) (opt)->blk_sz
 
+#define OPTION_SET_LIMITS_DOUBLE(options, opt) \
+  options->var_type= GET_DOUBLE; \
+  options->def_value= (longlong) getopt_double2ulonglong((opt)->def_val); \
+  options->min_value= (longlong) getopt_double2ulonglong((opt)->min_val); \
+  options->max_value= getopt_double2ulonglong((opt)->max_val); \
+  options->block_size= (long) (opt)->blk_sz;
+
 
 static void plugin_opt_set_limits(struct my_option *options,
                                   const struct st_mysql_sys_var *opt)
@@ -3142,6 +3188,9 @@ static void plugin_opt_set_limits(struct my_option *options,
                         GET_STR_ALLOC : GET_STR);
     options->def_value= (intptr) ((sysvar_str_t*) opt)->def_val;
     break;
+  case PLUGIN_VAR_DOUBLE:
+    OPTION_SET_LIMITS_DOUBLE(options, (sysvar_double_t*) opt);
+    break;
   /* threadlocal variables */
   case PLUGIN_VAR_INT | PLUGIN_VAR_THDLOCAL:
     OPTION_SET_LIMITS(GET_INT, options, (thdvar_int_t*) opt);
@@ -3161,6 +3210,9 @@ static void plugin_opt_set_limits(struct my_option *options,
   case PLUGIN_VAR_LONGLONG | PLUGIN_VAR_UNSIGNED | PLUGIN_VAR_THDLOCAL:
     OPTION_SET_LIMITS(GET_ULL, options, (thdvar_ulonglong_t*) opt);
     break;
+  case PLUGIN_VAR_DOUBLE | PLUGIN_VAR_THDLOCAL:
+    OPTION_SET_LIMITS_DOUBLE(options, (thdvar_double_t*) opt);
+    break;
   case PLUGIN_VAR_ENUM | PLUGIN_VAR_THDLOCAL:
     options->var_type= GET_ENUM;
     options->typelib= ((thdvar_enum_t*) opt)->typelib;
@@ -3323,6 +3375,9 @@ static int construct_options(MEM_ROOT *mem_root, struct st_plugin_int *tmp,
     case PLUGIN_VAR_SET:
       ((thdvar_set_t *) opt)->resolve= mysql_sys_var_ulonglong;
       break;
+    case PLUGIN_VAR_DOUBLE:
+      ((thdvar_double_t *) opt)->resolve= mysql_sys_var_double;
+      break;
     default:
       sql_print_error("Unknown variable type code 0x%x in plugin '%s'.",
                       opt->flags, plugin_name);
@@ -3386,6 +3441,12 @@ static int construct_options(MEM_ROOT *mem_root, struct st_plugin_int *tmp,
       if (!opt->update)
         opt->update= update_func_longlong;
       break;
+    case PLUGIN_VAR_DOUBLE:
+      if (!opt->check)
+        opt->check= check_func_double;
+      if (!opt->update)
+        opt->update= update_func_double;
+      break;
     default:
       sql_print_error("Unknown variable type code 0x%x in plugin '%s'.",
                       opt->flags, plugin_name);
diff --git a/sql/sys_vars.h b/sql/sys_vars.h
index ca6e7d40b0e..443e843bdde 100644
--- a/sql/sys_vars.h
+++ b/sql/sys_vars.h
@@ -729,13 +729,14 @@ public:
           const char *substitute=0,
           int parse_flag= PARSE_NORMAL)
     : sys_var(&all_sys_vars, name_arg, comment, flag_args, off, getopt.id,
-              getopt.arg_type, SHOW_DOUBLE, (longlong) double2ulonglong(def_val),
+              getopt.arg_type, SHOW_DOUBLE,
+              (longlong) getopt_double2ulonglong(def_val),
               lock, binlog_status_arg, on_check_func, on_update_func,
               substitute, parse_flag)
   {
     option.var_type= GET_DOUBLE;
-    option.min_value= (longlong) double2ulonglong(min_val);
-    option.max_value= (longlong) double2ulonglong(max_val);
+    option.min_value= (longlong) getopt_double2ulonglong(min_val);
+    option.max_value= (longlong) getopt_double2ulonglong(max_val);
     global_var(double)= (double)option.def_value;
     DBUG_ASSERT(min_val < max_val);
     DBUG_ASSERT(min_val <= def_val);
@@ -767,7 +768,7 @@ public:
   void session_save_default(THD *thd, set_var *var)
   { var->save_result.double_value= global_var(double); }
   void global_save_default(THD *thd, set_var *var)
-  { var->save_result.double_value= (double)option.def_value; }
+  { var->save_result.double_value= getopt_ulonglong2double(option.def_value); }
 };
 
 /**