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//# ColumnCache.h: A caching object for a table column
//# Copyright (C) 1997
//# Associated Universities, Inc. Washington DC, USA.
//#
//# This library is free software; you can redistribute it and/or modify it
//# under the terms of the GNU Library General Public License as published by
//# the Free Software Foundation; either version 2 of the License, or (at your
//# option) any later version.
//#
//# This library 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 Library General Public
//# License for more details.
//#
//# You should have received a copy of the GNU Library General Public License
//# along with this library; if not, write to the Free Software Foundation,
//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
//#
//# Correspondence concerning AIPS++ should be addressed as follows:
//# Internet email: aips2-request@nrao.edu.
//# Postal address: AIPS++ Project Office
//# National Radio Astronomy Observatory
//# 520 Edgemont Road
//# Charlottesville, VA 22903-2475 USA
//#
//# $Id$
#ifndef TABLES_COLUMNCACHE_H
#define TABLES_COLUMNCACHE_H
//# Includes
#include <cassert>
#include <limits>
#include <casacore/casa/aips.h>
namespace casacore { //# NAMESPACE CASACORE - BEGIN
// <summary>
// A caching object for a table column.
// </summary>
// <use visibility=local>
// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="">
// </reviewed>
// <prerequisite>
//# Classes you should understand before using this one.
// <li> <linkto class=ScalarColumn>ScalarColumn</linkto>
// </prerequisite>
// <synopsis>
// ColumnCache acts as a cache for a table column.
// It contains a pointer to data and the start and end row number
// for which these data are valid. An increment is part of the object
// and is usually 0 or 1. The value 0 is used for data which is
// valid for multiple rows (as used in
// <linkto class=IncrementalStMan>IncrementalStMan</linkto>).
// The value 1 is used for data stored consecutevily in a buffer for
// each row (as used in <linkto class=StManAipsIO>StManAipsIO</linkto>).
// <p>
// The ColumnCache object is created and updated by the data manager.
// The top level <linkto class=ScalarColumn>ScalarColumn</linkto> object
// contains a pointer to the cache object. In this way the
// <src>ScalarColumn::get</src> can often be executed by a few inlined
// statements which improves performance considerably.
// <p>
// The <src>invalidate</src> function can be used to invalidate the
// cache. This is for instance needed when a table lock is acquired
// or released to be sure that the cache gets refreshed.
// </synopsis>
// <motivation>
// This class was developed to improve the performance for getting a scalar.
// </motivation>
// <todo asof="$DATE:$">
// <li>For ConcatColumn add the ability to have other ColumnCache objects
// using this one and invalidate them as well.
// </todo>
class ColumnCache
{
public:
// Constructor.
// It sets the increment to 1 and calls invalidate.
ColumnCache();
// Set the increment to the given value.
void setIncrement (rownr_t increment);
// Set the start and end row number for which the given data pointer
// is valid.
void set (rownr_t startRow, rownr_t endRow, const void* dataPtr);
// Invalidate the cache.
// This clears the data pointer and sets startRow>endRow.
void invalidate();
// Calculate the offset in the cached data for the given row.
// -1 is returned if the row is not within the cached rows.
Int64 offset (rownr_t rownr) const;
// Give a pointer to the data.
// The calling function has to do a proper cast after which the
// calculated offset can be added to get the proper data.
const void* dataPtr() const;
// Give the start, end (including), and increment row number
// of the cached column values.
rownr_t start() const
{ return itsStart; }
rownr_t end() const
{ return itsEnd; }
rownr_t incr() const
{ return itsIncr; }
private:
rownr_t itsStart;
rownr_t itsEnd;
rownr_t itsIncr;
const void* itsData;
};
inline void ColumnCache::setIncrement (rownr_t increment)
{
itsIncr = increment;
}
inline void ColumnCache::invalidate()
{
set (1, 0, 0);
}
inline Int64 ColumnCache::offset (rownr_t rownr) const
{
if (rownr < itsStart || rownr > itsEnd) {
return -1;
}
const rownr_t offset = (rownr - itsStart) * itsIncr;
assert(offset <= static_cast<rownr_t>(std::numeric_limits<Int64>::max()));
return Int64(offset);
}
inline const void* ColumnCache::dataPtr() const
{
return itsData;
}
} //# NAMESPACE CASACORE - END
#endif
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