1 files changed, 76 insertions, 0 deletions
diff --git a/storage/innobase/include/buf0block_hint.h b/storage/innobase/include/buf0block_hint.h
new file mode 100644
index 00000000000..ee48e7ce6d2
--- /dev/null
+++ b/storage/innobase/include/buf0block_hint.h
@@ -0,0 +1,76 @@
+/*****************************************************************************
+
+Copyright (c) 2020, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2020, MariaDB Corporation.
+This program is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License, version 2.0, as published by the
+Free Software Foundation.
+
+This program is also distributed with certain software (including but not
+limited to OpenSSL) that is licensed under separate terms, as designated in a
+particular file or component or in included license documentation. The authors
+of MySQL hereby grant you an additional permission to link the program and
+your derivative works with the separately licensed software that they have
+included with MySQL.
+
+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, version 2.0,
+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 St, Fifth Floor, Boston, MA 02110-1301  USA
+
+*****************************************************************************/
+#pragma once
+#include "buf0buf.h"
+
+namespace buf {
+class Block_hint {
+public:
+  /** Stores the pointer to the block, which is currently buffer-fixed.
+  @param  block   a pointer to a buffer-fixed block to be stored */
+  inline void store(buf_block_t *block)
+  {
+    ut_ad(block->page.buf_fix_count());
+    m_block= block;
+    m_page_id= block->page.id();
+  }
+
+  /** Clears currently stored pointer. */
+  inline void clear() { m_block= nullptr; }
+
+  /** Invoke f on m_block(which may be null)
+  @param  f   The function to be executed. It will be passed the pointer.
+              If you wish to use the block pointer subsequently,
+	      you need to ensure you buffer-fix it before returning from f.
+  @return the return value of f
+  */
+  template <typename F>
+  bool run_with_hint(const F &f)
+  {
+    buffer_fix_block_if_still_valid();
+    /* m_block could be changed during f() call, so we use local
+    variable to remember which block we need to unfix */
+    buf_block_t *block= m_block;
+    bool res= f(block);
+    if (block)
+      buf_block_buf_fix_dec(block);
+    return res;
+  }
+
+  buf_block_t *block() const { return m_block; }
+
+ private:
+  /** The block pointer stored by store(). */
+  buf_block_t *m_block= nullptr;
+  /** If m_block is non-null, the m_block->page.id at time it was stored. */
+  page_id_t m_page_id{0, 0};
+
+  /** A helper function which checks if m_block is not a dangling pointer and
+  still points to block with page with m_page_id and if so, buffer-fixes it,
+  otherwise clear()s it */
+  void buffer_fix_block_if_still_valid();
+};
+}  // namespace buf