MMapIO.h

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00001 //# MMapIO.h: Memory-mapped IO on a file
00002 //#
00003 //#  Copyright (C) 2009
00004 //# Associated Universities, Inc. Washington DC, USA.
00005 //#
00006 //# This library is free software; you can redistribute it and/or modify it
00007 //# under the terms of the GNU Library General Public License as published by
00008 //# the Free Software Foundation; either version 2 of the License, or (at your
00009 //# option) any later version.
00010 //#
00011 //# This library is distributed in the hope that it will be useful, but WITHOUT
00012 //# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
00013 //# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
00014 //# License for more details.
00015 //#
00016 //# You should have received a copy of the GNU Library General Public License
00017 //# along with this library; if not, write to the Free Software Foundation,
00018 //# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
00019 //#
00020 //# Correspondence concerning AIPS++ should be addressed as follows:
00021 //#        Internet email: aips2-request@nrao.edu.
00022 //#        Postal address: AIPS++ Project Office
00023 //#                        National Radio Astronomy Observatory
00024 //#                        520 Edgemont Road
00025 //#                        Charlottesville, VA 22903-2475 USA
00026 //#
00027 //#  $Id$
00028 
00029 #ifndef CASA_MMAPIO_H
00030 #define CASA_MMAPIO_H
00031 
00032 //# Includes
00033 #include <casacore/casa/aips.h>
00034 #include <casacore/casa/IO/MMapfdIO.h>
00035 #include <casacore/casa/OS/RegularFile.h>
00036 
00037 namespace casacore
00038 {
00039 
00040 // <summary>
00041 // Memory-mapped IO on a file.
00042 // </summary>
00043 
00044 // <synopsis>
00045 // Memory-mapped IO lets the OS take care of caching file segments.
00046 // This is particularly useful for the Tiled Storage Manager which keeps a
00047 // cache of tiles. When using memory-mapped IO it does not need to do that
00048 // anymore.
00049 //
00050 // On 32-bit systems its use is limited because for large files the 4 GB
00051 // memory space is insufficient. However, for 64-bit systems the memory
00052 // space is large enough to make use of it.
00053 //
00054 // In the general case there is direct access to the mapped file space.
00055 // The read and write methods copies the data into/from a buffer.
00056 // However, to avoid the copying it is possible to get a direct pointer
00057 // to the mapped data. This should be used with care, because writing to
00058 // it will cause a segmentation if the file is readonly. If the file is
00059 // writable, writing into the mapped data segment means changing the file
00060 // contents.
00061 // </synopsis>
00062 
00063 class MMapIO: public MMapfdIO
00064 {
00065 public:
00066   // Open the given file and map it entirely into memory with read access.
00067   // The map has write access if the file is opened for write.
00068   explicit MMapIO (const RegularFile& regularFile,
00069                    ByteIO::OpenOption = ByteIO::Old);
00070 
00071   // Destructor.
00072   // It will flush and unmap the file.
00073   ~MMapIO();
00074 
00075 private:
00076   // Forbid copy constructor and assignment
00077   // <group>
00078   MMapIO (const MMapIO&);
00079   MMapIO& operator= (const MMapIO&);
00080   // </group>
00081 };
00082 
00083 } // end namespace
00084 
00085 #endif
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