casacore
MMapIO.h
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1 //# MMapIO.h: Memory-mapped IO on a file
2 //#
3 //# Copyright (C) 2009
4 //# Associated Universities, Inc. Washington DC, USA.
5 //#
6 //# This library is free software; you can redistribute it and/or modify it
7 //# under the terms of the GNU Library General Public License as published by
8 //# the Free Software Foundation; either version 2 of the License, or (at your
9 //# option) any later version.
10 //#
11 //# This library is distributed in the hope that it will be useful, but WITHOUT
12 //# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 //# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
14 //# License for more details.
15 //#
16 //# You should have received a copy of the GNU Library General Public License
17 //# along with this library; if not, write to the Free Software Foundation,
18 //# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
19 //#
20 //# Correspondence concerning AIPS++ should be addressed as follows:
21 //# Internet email: aips2-request@nrao.edu.
22 //# Postal address: AIPS++ Project Office
23 //# National Radio Astronomy Observatory
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26 //#
27 //# $Id$
28 
29 #ifndef CASA_MMAPIO_H
30 #define CASA_MMAPIO_H
31 
32 //# Includes
33 #include <casacore/casa/aips.h>
34 #include <casacore/casa/IO/MMapfdIO.h>
35 #include <casacore/casa/OS/RegularFile.h>
36 
37 namespace casacore
38 {
39 
40 // <summary>
41 // Memory-mapped IO on a file.
42 // </summary>
43 
44 // <synopsis>
45 // Memory-mapped IO lets the OS take care of caching file segments.
46 // This is particularly useful for the Tiled Storage Manager which keeps a
47 // cache of tiles. When using memory-mapped IO it does not need to do that
48 // anymore.
49 //
50 // On 32-bit systems its use is limited because for large files the 4 GB
51 // memory space is insufficient. However, for 64-bit systems the memory
52 // space is large enough to make use of it.
53 //
54 // In the general case there is direct access to the mapped file space.
55 // The read and write methods copies the data into/from a buffer.
56 // However, to avoid the copying it is possible to get a direct pointer
57 // to the mapped data. This should be used with care, because writing to
58 // it will cause a segmentation if the file is readonly. If the file is
59 // writable, writing into the mapped data segment means changing the file
60 // contents.
61 // </synopsis>
62 
63 class MMapIO: public MMapfdIO
64 {
65 public:
66  // Open the given file and map it entirely into memory with read access.
67  // The map has write access if the file is opened for write.
68  explicit MMapIO (const RegularFile& regularFile,
70 
71  // Destructor.
72  // It will flush and unmap the file.
74 
75 private:
76  // Forbid copy constructor and assignment
77  // <group>
78  MMapIO (const MMapIO&);
80  // </group>
81 };
82 
83 } // end namespace
84 
85 #endif
OpenOption
Define the possible ByteIO open options.
Definition: ByteIO.h:65
MMapIO(const RegularFile &regularFile, ByteIO::OpenOption=ByteIO::Old)
Open the given file and map it entirely into memory with read access.
~MMapIO()
Destructor.
MMapIO & operator=(const MMapIO &)
MMapIO(const MMapIO &)
Forbid copy constructor and assignment.
this file contains all the compiler specific defines
Definition: mainpage.dox:28