/*****************************************************************************

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Copyright (c) 2019, 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
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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this program; if not, write to the Free Software Foundation, Inc.,
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*****************************************************************************/

/**************************************************//**
@file include/read0read.h
Cursor read

Created 2/16/1997 Heikki Tuuri
*******************************************************/

#ifndef read0read_h
#define read0read_h

#include "read0types.h"

#include <algorithm>

/** The MVCC read view manager */
class MVCC {
public:
	/** Constructor
	@param size		Number of views to pre-allocate */
	explicit MVCC(ulint size);

	/** Destructor.
	Free all the views in the m_free list */
	~MVCC();

	/**
	Allocate and create a view.
	@param view		view owned by this class created for the
				caller. Must be freed by calling close()
	@param trx		transaction creating the view */
	void view_open(ReadView*& view, trx_t* trx);

	/**
	Close a view created by view_open().
	@param view		view allocated by view_open()
	@param own_mutex	whether the caller owns trx_sys_t::mutex */
	void view_close(ReadView*& view, bool own_mutex);

	/**
	Release a view that is inactive but not closed. Caller must own
	the trx_sys_t::mutex.
	@param view		View to release */
	void view_release(ReadView*& view);

	/** Clones the oldest view and stores it in view. No need to
	call view_close(). The caller owns the view that is passed in.
	It will also move the closed views from the m_views list to the
	m_free list. This function is called by Purge to create it view.
	@param view		Preallocated view, owned by the caller */
	void clone_oldest_view(ReadView* view);

	/**
	@return the number of active views */
	ulint size() const;

	/**
	@return true if the view is active and valid */
	static bool is_view_active(ReadView* view)
	{
		ut_a(view != reinterpret_cast<ReadView*>(0x1));

		return(view != NULL && !(intptr_t(view) & 0x1));
	}

	/**
	Set the view creator transaction id. Note: This shouldbe set only
	for views created by RW transactions. */
	static void set_view_creator_trx_id(ReadView* view, trx_id_t id);

private:

	/**
	Validates a read view list. */
	bool validate() const;

	/**
	Find a free view from the active list, if none found then allocate
	a new view. This function will also attempt to move delete marked
	views from the active list to the freed list.
	@return a view to use */
	inline ReadView* get_view();

	/**
	Get the oldest view in the system. It will also move the delete
	marked read views from the views list to the freed list.
	@return oldest view if found or NULL */
	inline ReadView* get_oldest_view() const;

private:
	// Prevent copying
	MVCC(const MVCC&);
	MVCC& operator=(const MVCC&);

private:
	typedef UT_LIST_BASE_NODE_T(ReadView) view_list_t;

	/** Free views ready for reuse. */
	view_list_t		m_free;

	/** Active and closed views, the closed views will have the
	creator trx id set to TRX_ID_MAX */
	view_list_t		m_views;
};

#endif /* read0read_h */