sql_cursor.h

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/* Copyright (c) 2005, 2021, Oracle and/or its affiliates.
 
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#ifndef _sql_cursor_h_
#define _sql_cursor_h_
 
#include <stddef.h>
#include <sys/types.h>
#include <new>
 
#include "sql/sql_class.h" /* Query_arena */
 
class Query_result;
struct MEM_ROOT;
 
/**
  @file
 
  Declarations for implementation of server side cursors. Only
  read-only non-scrollable cursors are currently implemented.
*/
 
/**
  Server_side_cursor -- an interface for materialized
  implementation of cursors. All cursors are self-contained
  (created in their own memory root).  For that reason they must
  be deleted only using a pointer to Server_side_cursor, not to
  its base class.
*/
 
class Server_side_cursor {
 public:
  /**
    For allocation of Handler objects for the temporary table. The prepared
    statement's mem_root cannot be used, since the handler may be created and
    deleted several times. The execution mem_root cannot be used since
    creation of and retrieval from a cursor are in different executions.
  */
  MEM_ROOT mem_root;
 
 protected:
  Query_arena m_arena;
  /** Row destination used for fetch */
  Query_result *result;
 
 public:
  Server_side_cursor(Query_result *result_arg)
      : m_arena(&mem_root, Query_arena::STMT_INITIALIZED), result(result_arg) {
    init_sql_alloc(key_memory_TABLE, &mem_root, 1024, 1024);
  }
  virtual bool is_open() const = 0;
 
  virtual bool open(THD *thd) = 0;
  virtual bool fetch(ulong num_rows) = 0;
  virtual void close() = 0;
  virtual ~Server_side_cursor() { mem_root.Clear(); }
  static void *operator new(size_t size, MEM_ROOT *mem_root,
                            const std::nothrow_t & = std::nothrow) noexcept {
    return mem_root->Alloc(size);
  }
  static void operator delete(void *, size_t) {}
  static void operator delete(
      void *, MEM_ROOT *, const std::nothrow_t &) noexcept { /* never called */
  }
};
 
bool mysql_open_cursor(THD *thd, Query_result *result,
                       Server_side_cursor **res);
 
#endif /* _sql_cusor_h_ */