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mariadb/sql/sp_rcontext_handler.h
Alexander Barkov e6961ea311 MDEV-20034 Add support for the pre-defined weak SYS_REFCURSOR 
This patch adds support for SYS_REFCURSOR (a weakly typed cursor)
for both sql_mode=ORACLE and sql_mode=DEFAULT.

Works as a regular stored routine variable, parameter and return value:

- can be passed as an IN parameter to stored functions and procedures
- can be passed as an INOUT and OUT parameter to stored procedures
- can be returned from a stored function

Note, strongly typed REF CURSOR will be added separately.

Note, to maintain dependencies easier, some parts of sql_class.h
and item.h were moved to new header files:

- select_results.h:
  class select_result_sink
  class select_result
  class select_result_interceptor

- sp_cursor.h:
  class sp_cursor_statistics
  class sp_cursor

- sp_rcontext_handler.h
  class Sp_rcontext_handler and its descendants

The implementation consists of the following parts:
- A new class sp_cursor_array deriving from Dynamic_array

- A new class Statement_rcontext which contains data shared
  between sub-statements of a compound statement.
  It has a member m_statement_cursors of the sp_cursor_array data type,
  as well as open cursor counter. THD inherits from Statement_rcontext.

- A new data type handler Type_handler_sys_refcursor in plugins/type_cursor/
  It is designed to store uint16 references -
  positions of the cursor in THD::m_statement_cursors.

- Type_handler_sys_refcursor suppresses some derived numeric features.
  When a SYS_REFCURSOR variable is used as an integer an error is raised.

- A new abstract class sp_instr_fetch_cursor. It's needed to share
  the common code between "OPEN cur" (for static cursors) and
  "OPER cur FOR stmt" (for SYS_REFCURSORs).

- New sp_instr classes:
  * sp_instr_copen_by_ref      - OPEN sys_ref_curor FOR stmt;
  * sp_instr_cfetch_by_ref     - FETCH sys_ref_cursor INTO targets;
  * sp_instr_cclose_by_ref     - CLOSE sys_ref_cursor;
  * sp_instr_destruct_variable - to destruct SYS_REFCURSOR variables when
                                 the execution goes out of the BEGIN..END block
                                 where SYS_REFCURSOR variables are declared.
- New methods in LEX:
  * sp_open_cursor_for_stmt   - handles "OPEN sys_ref_cursor FOR stmt".
  * sp_add_instr_fetch_cursor - "FETCH cur INTO targets" for both
                                static cursors and SYS_REFCURSORs.
  * sp_close - handles "CLOSE cur" both for static cursors and SYS_REFCURSORs.

- Changes in cursor functions to handle both static cursors and SYS_REFCURSORs:
  * Item_func_cursor_isopen
  * Item_func_cursor_found
  * Item_func_cursor_notfound
  * Item_func_cursor_rowcount

- A new system variable @@max_open_cursors - to limit the number
  of cursors (static and SYS_REFCURSORs) opened at the same time.
  Its allowed range is [0-65536], with 50 by default.

- A new virtual method Type_handler::can_return_bool() telling
  if calling item->val_bool() is allowed for Items of this data type,
  or if otherwise the "Illegal parameter for operation" error should be raised
  at fix_fields() time.

- New methods in Sp_rcontext_handler:
  * get_cursor()
  * get_cursor_by_ref()

- A new class Sp_rcontext_handler_statement to handle top level statement
  wide cursors which are shared by all substatements.

- A new virtual method expr_event_handler() in classes Item and Field.
  It's needed to close (and make available for a new OPEN)
  unused THD::m_statement_cursors elements which do not have any references
  any more. It can happen in various moments in time, e.g.
  * after evaluation parameters of an SQL routine
  * after assigning a cursor expression into a SYS_REFCURSOR variable
  * when leaving a BEGIN..END block with SYS_REFCURSOR variables
  * after setting OUT/INOUT routine actual parameters from formal
    parameters.
2025-03-18 18:31:28 +01:00

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#ifndef SP_RCONTEXT_HANDLER_INCLUDED
#define SP_RCONTEXT_HANDLER_INCLUDED
/* Copyright (c) 2009, 2025, MariaDB Corporation.
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 Street, Fifth Floor, Boston, MA 02110-1335 USA */
class sp_rcontext;
class sp_cursor;
/**
A helper class to handle the run time context of various components of SP:
Variables:
- local SP variables and SP parameters
- PACKAGE BODY routine variables
- (there will be more kinds in the future)
Cursors:
- static cursors
- SYS_REFCURSORs
*/
class Sp_rcontext_handler
{
public:
/*
Get a cursor using its direct address or a reference.
addr_or_ref.deref_rcontext_handler()==nullptr means
that addr_or_ref contains the direct address of the cursor.
A not-null addr_or_ref.deref_rcontext_handler() value
means that it is a reference and should be dereferenced.
*/
static sp_cursor *get_cursor(THD *thd,
const sp_rcontext_ref &addr_or_ref)
{
return addr_or_ref.deref_rcontext_handler() ?
addr_or_ref.deref_rcontext_handler()->get_cursor_by_ref(thd, addr_or_ref,
false) :
addr_or_ref.rcontext_handler()->get_cursor(thd, addr_or_ref.offset());
}
/*
Get a cursor using its direct address or a reference.
If the cursor is not found or is not open,
the ER_SP_CURSOR_NOT_OPEN error is raised.
*/
static sp_cursor *get_open_cursor_or_error(THD *thd,
const sp_rcontext_ref &addr_or_ref);
virtual ~Sp_rcontext_handler() = default;
/**
A prefix used for SP variable names in queries:
- EXPLAIN EXTENDED
- SHOW PROCEDURE CODE
Local variables and SP parameters have empty prefixes.
Package body variables are marked with a special prefix.
This improves readability of the output of these queries,
especially when a local variable or a parameter has the same
name with a package body variable.
*/
virtual const LEX_CSTRING *get_name_prefix() const= 0;
/**
At execution time THD->spcont points to the run-time context (sp_rcontext)
of the currently executed routine.
Local variables store their data in the sp_rcontext pointed by thd->spcont.
Package body variables store data in separate sp_rcontext that belongs
to the package.
This method provides access to the proper sp_rcontext structure,
depending on the SP variable kind.
*/
virtual sp_rcontext *get_rcontext(sp_rcontext *ctx) const= 0;
virtual Item_field *get_variable(THD *thd, uint offset) const= 0;
virtual sp_cursor *get_cursor(THD *thd, uint offset) const= 0;
virtual sp_cursor *get_cursor_by_ref(THD *thd,
const sp_rcontext_addr &ref,
bool for_open) const= 0;
};
class Sp_rcontext_handler_local final :public Sp_rcontext_handler
{
public:
const LEX_CSTRING *get_name_prefix() const override;
sp_rcontext *get_rcontext(sp_rcontext *ctx) const override;
Item_field *get_variable(THD *thd, uint offset) const override;
sp_cursor *get_cursor(THD *thd, uint offset) const override;
sp_cursor *get_cursor_by_ref(THD *thd, const sp_rcontext_addr &ref,
bool for_open) const override
{
DBUG_ASSERT(0); // References to static cursors are not supported
return nullptr;
}
};
class Sp_rcontext_handler_package_body final :public Sp_rcontext_handler
{
public:
const LEX_CSTRING *get_name_prefix() const override;
sp_rcontext *get_rcontext(sp_rcontext *ctx) const override;
Item_field *get_variable(THD *thd, uint offset) const override;
sp_cursor *get_cursor(THD *thd, uint offset) const override
{
/*
There are no package body wide static cursors yet:
MDEV-36053 Syntax error on a CURSOR..IS declaration in PACKAGE BODY
*/
DBUG_ASSERT(0);
return nullptr;
}
sp_cursor *get_cursor_by_ref(THD *thd, const sp_rcontext_addr &ref,
bool for_open) const override
{
DBUG_ASSERT(0); // References to static cursors are not supported
return nullptr;
}
};
class Sp_rcontext_handler_statement final :public Sp_rcontext_handler
{
public:
const LEX_CSTRING *get_name_prefix() const override;
sp_rcontext *get_rcontext(sp_rcontext *ctx) const override
{
DBUG_ASSERT(0); // There are no session wide SP variables yet.
return nullptr;
}
Item_field *get_variable(THD *thd, uint offset) const override
{
DBUG_ASSERT(0); // There are no session wide SP variables yet.
return nullptr;
}
sp_cursor *get_cursor(THD *thd, uint offset) const override;
sp_cursor *get_cursor_by_ref(THD *thd, const sp_rcontext_addr &ref,
bool for_open) const override;
};
extern MYSQL_PLUGIN_IMPORT
Sp_rcontext_handler_local sp_rcontext_handler_local;
extern MYSQL_PLUGIN_IMPORT
Sp_rcontext_handler_package_body sp_rcontext_handler_package_body;
extern MYSQL_PLUGIN_IMPORT
Sp_rcontext_handler_statement sp_rcontext_handler_statement;
#endif // SP_RCONTEXT_HANDLER_INCLUDED
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