BucketMapped.h

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// # BucketMapped.h: File buckets by means of file mapping
// # Copyright (C) 2009
// # 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: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef CASA_BUCKETMAPPED_H
#define CASA_BUCKETMAPPED_H
 
// # Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/IO/BucketBase.h>
#include <casacore/casa/IO/MMapfdIO.h>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// <summary>
// Use file mapping for buckets in a part of a file
// </summary>
 
// <use visibility=export>
 
// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="" demos="">
// </reviewed>
 
// <prerequisite>
// # Classes you should understand before using this one.
//   <li> <linkto class=BucketFile>BucketFile</linkto>
// </prerequisite>
 
// <etymology>
// BucketMapped uses memory-mapped files for bucket access.
// </etymology>
 
// <synopsis>
// BucketMapped is similar to class
// <linkto class=BucketCache>BucketCache</linkto> and is meant to be used by
// the storage managers of the Table System.
//
// It gives access to buckets in a file by means of memory-mapped files.
// However, its functionality is a subset of BucketCache and is only meant
// to be used by the Tiled Storage Managers. If The Standard and Incremental
// Storage Manager also want to use it, functions like <src>extend</src>
// needs to be added to this class. Also support for a free bucket list needs
// to be added.
// </synopsis>
 
// <motivation>
// Use of BucketCache is sub-optimal when having large buckets and more or
// less random IO. Memory-mapping behaves much better.
// </motivation>
 
class BucketMapped : public BucketBase {
 public:
  // Create the cache for (part of) a file.
  // The file part mapped into memory starts at startOffset. Its length is
  // bucketSize*nrOfBuckets bytes.
  // If the file is smaller, the remainder is indicated as an extension
  // similarly to the behaviour of function extend.
  BucketMapped(BucketFile* file, Int64 startOffset, uInt bucketSize, uInt nrOfBuckets);
 
  // Unmap the file
  ~BucketMapped();
 
  // Get a readonly pointer to the given bucket in memory.
  const char* getBucket(uInt bucketNr);
 
  // Get a writable pointer to the given bucket in memory.
  // It sets the hasWritten flag.
  char* getrwBucket(uInt bucketNr) {
    itsHasWritten = True;
    return const_cast<char*>(getBucket(bucketNr));
  }
 
 private:
  // Copy constructor is not possible.
  BucketMapped(const BucketMapped&);
 
  // Assignment is not possible.
  BucketMapped& operator=(const BucketMapped&);
 
  // Flush the file.
  virtual void doFlush();
 
  // Do the actual resync-ing.
  virtual void doResync();
 
  // Extend the file with the given number of buckets.
  virtual void doExtend(uInt nrBucket);
 
  // Initialize the bucket buffer.
  // The uninitialized buckets before this bucket are also initialized.
  virtual void initializeBuckets(uInt bucketNr);
};
 
}  // namespace casacore
 
#endif