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76 lines
2.8 KiB
C++
76 lines
2.8 KiB
C++
/*****************************************************************************
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Copyright (c) 2020, Oracle and/or its affiliates. All Rights Reserved.
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Copyright (c) 2020, MariaDB Corporation.
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This program is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License, version 2.0, as published by the
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Free Software Foundation.
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This program is also distributed with certain software (including but not
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limited to OpenSSL) that is licensed under separate terms, as designated in a
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particular file or component or in included license documentation. The authors
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of MySQL hereby grant you an additional permission to link the program and
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your derivative works with the separately licensed software that they have
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included with MySQL.
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This program is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License, version 2.0,
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for more details.
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You should have received a copy of the GNU General Public License along with
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this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*****************************************************************************/
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#pragma once
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#include "buf0buf.h"
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namespace buf {
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class Block_hint {
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public:
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/** Stores the pointer to the block, which is currently buffer-fixed.
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@param block a pointer to a buffer-fixed block to be stored */
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inline void store(buf_block_t *block)
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{
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ut_ad(block->page.buf_fix_count());
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m_block= block;
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m_page_id= block->page.id();
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}
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/** Clears currently stored pointer. */
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inline void clear() { m_block= nullptr; }
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/** Invoke f on m_block(which may be null)
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@param f The function to be executed. It will be passed the pointer.
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If you wish to use the block pointer subsequently,
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you need to ensure you buffer-fix it before returning from f.
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@return the return value of f
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*/
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template <typename F>
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bool run_with_hint(const F &f)
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{
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buffer_fix_block_if_still_valid();
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/* m_block could be changed during f() call, so we use local
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variable to remember which block we need to unfix */
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buf_block_t *block= m_block;
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bool res= f(block);
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if (block)
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buf_block_buf_fix_dec(block);
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return res;
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}
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buf_block_t *block() const { return m_block; }
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private:
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/** The block pointer stored by store(). */
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buf_block_t *m_block= nullptr;
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/** If m_block is non-null, the m_block->page.id at time it was stored. */
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page_id_t m_page_id{0, 0};
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/** A helper function which checks if m_block is not a dangling pointer and
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still points to block with page with m_page_id and if so, buffer-fixes it,
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otherwise clear()s it */
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void buffer_fix_block_if_still_valid();
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};
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} // namespace buf
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