BucketMapped.h

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00001 //# BucketMapped.h: File buckets by means of file mapping
00002 //# Copyright (C) 2009
00003 //# Associated Universities, Inc. Washington DC, USA.
00004 //#
00005 //# This library is free software; you can redistribute it and/or modify it
00006 //# under the terms of the GNU Library General Public License as published by
00007 //# the Free Software Foundation; either version 2 of the License, or (at your
00008 //# option) any later version.
00009 //#
00010 //# This library is distributed in the hope that it will be useful, but WITHOUT
00011 //# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
00012 //# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
00013 //# License for more details.
00014 //#
00015 //# You should have received a copy of the GNU Library General Public License
00016 //# along with this library; if not, write to the Free Software Foundation,
00017 //# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
00018 //#
00019 //# Correspondence concerning AIPS++ should be addressed as follows:
00020 //#        Internet email: aips2-request@nrao.edu.
00021 //#        Postal address: AIPS++ Project Office
00022 //#                        National Radio Astronomy Observatory
00023 //#                        520 Edgemont Road
00024 //#                        Charlottesville, VA 22903-2475 USA
00025 //#
00026 //# $Id$
00027 
00028 #ifndef CASA_BUCKETMAPPED_H
00029 #define CASA_BUCKETMAPPED_H
00030 
00031 //# Includes
00032 #include <casacore/casa/aips.h>
00033 #include <casacore/casa/IO/BucketBase.h>
00034 #include <casacore/casa/IO/MMapfdIO.h>
00035 
00036 
00037 namespace casacore { //# NAMESPACE CASACORE - BEGIN
00038 
00039   // <summary>
00040   // Use file mapping for buckets in a part of a file
00041   // </summary>
00042 
00043   // <use visibility=export>
00044 
00045   // <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="" demos="">
00046   // </reviewed>
00047 
00048   // <prerequisite>
00049   //# Classes you should understand before using this one.
00050   //   <li> <linkto class=BucketFile>BucketFile</linkto>
00051   // </prerequisite>
00052 
00053   // <etymology>
00054   // BucketMapped uses memory-mapped files for bucket access.
00055   // </etymology>
00056 
00057   // <synopsis>
00058   // BucketMapped is similar to class
00059   // <linkto class=BucketCache>BucketCache</linkto> and is meant to be used by
00060   // the storage managers of the Table System.
00061   //
00062   // It gives access to buckets in a file by means of memory-mapped files.
00063   // However, its functionality is a subset of BucketCache and is only meant
00064   // to be used by the Tiled Storage Managers. If The Standard and Incremental
00065   // Storage Manager also want to use it, functions like <src>extend</src>
00066   // needs to be added to this class. Also support for a free bucket list needs
00067   // to be added.
00068   // </synopsis> 
00069 
00070   // <motivation>
00071   // Use of BucketCache is sub-optimal when having large buckets and more or
00072   // less random IO. Memory-mapping behaves much better.
00073   // </motivation>
00074 
00075 
00076   class BucketMapped: public BucketBase
00077   {
00078   public:
00079     // Create the cache for (part of) a file.
00080     // The file part mapped into memory starts at startOffset. Its length is
00081     // bucketSize*nrOfBuckets bytes.
00082     // If the file is smaller, the remainder is indicated as an extension
00083     // similarly to the behaviour of function extend.
00084     BucketMapped (BucketFile* file, Int64 startOffset, uInt bucketSize,
00085                   uInt nrOfBuckets);
00086 
00087     // Unmap the file
00088     ~BucketMapped();
00089 
00090     // Get a readonly pointer to the given bucket in memory.
00091     const char* getBucket (uInt bucketNr);
00092 
00093     // Get a writable pointer to the given bucket in memory.
00094     // It sets the hasWritten flag.
00095     char* getrwBucket (uInt bucketNr)
00096     {
00097       itsHasWritten = True;
00098       return const_cast<char*>(getBucket(bucketNr));
00099     }
00100 
00101 private:
00102     // Copy constructor is not possible.
00103     BucketMapped (const BucketMapped&);
00104 
00105     // Assignment is not possible.
00106     BucketMapped& operator= (const BucketMapped&);
00107 
00108     // Flush the file.
00109     virtual void doFlush();
00110 
00111     // Do the actual resync-ing.
00112     virtual void doResync();
00113 
00114     // Extend the file with the given number of buckets.
00115     virtual void doExtend (uInt nrBucket);
00116 
00117     // Initialize the bucket buffer.
00118     // The uninitialized buckets before this bucket are also initialized.
00119     virtual void initializeBuckets (uInt bucketNr);
00120   };
00121 
00122 
00123 } //# NAMESPACE CASACORE - END
00124 
00125 #endif
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