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106 lines
2.8 KiB
C++
106 lines
2.8 KiB
C++
/* Copyright (C) 2005 MySQL AB
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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#ifndef TABLE_MAPPING_H
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#define TABLE_MAPPING_H
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/* Forward declarations */
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struct st_table;
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typedef st_table TABLE;
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/*
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CLASS table_mapping
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RESPONSIBILITIES
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The table mapping is used to map table id's to table pointers
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COLLABORATION
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RELAY_LOG For mapping table id:s to tables when receiving events.
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*/
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/*
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Guilhem to Mats:
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in the table_mapping class, the memory is allocated and never freed (until
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destruction). So this is a good candidate for allocating inside a MEM_ROOT:
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it gives the efficient allocation in chunks (like in expand()). So I have
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introduced a MEM_ROOT.
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Note that inheriting from Sql_alloc had no effect: it has effects only when
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"ptr= new table_mapping" is called, and this is never called. And it would
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then allocate from thd->mem_root which is a highly volatile object (reset
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from example after executing each query, see dispatch_command(), it has a
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free_root() at end); as the table_mapping object is supposed to live longer
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than a query, it was dangerous.
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A dedicated MEM_ROOT needs to be used, see below.
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*/
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class table_mapping {
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private:
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MEM_ROOT m_mem_root;
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public:
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enum enum_error {
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ERR_NO_ERROR = 0,
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ERR_LIMIT_EXCEEDED,
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ERR_MEMORY_ALLOCATION
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};
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table_mapping();
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~table_mapping();
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TABLE* get_table(ulong table_id);
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int set_table(ulong table_id, TABLE* table);
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int remove_table(ulong table_id);
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void clear_tables();
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ulong count() const { return m_table_ids.records; }
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private:
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/*
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This is a POD (Plain Old Data). Keep it that way (we apply offsetof() to
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it, which only works for PODs)
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*/
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struct entry {
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ulong table_id;
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union {
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TABLE *table;
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entry *next;
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};
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};
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entry *find_entry(ulong table_id)
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{
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return (entry *)hash_search(&m_table_ids,
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(byte*)&table_id,
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sizeof(table_id));
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}
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int expand();
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/*
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Head of the list of free entries; "free" in the sense that it's an
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allocated entry free for use, NOT in the sense that it's freed
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memory.
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*/
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entry *m_free;
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/* Correspondance between an id (a number) and a TABLE object */
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HASH m_table_ids;
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};
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#endif
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