/usr/include/casacore/casa/IO/MMapfdIO.h is in casacore-dev 2.2.0-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 | //# MMapfdIO.h: Memory-mapped IO on a file descriptor
//#
//# 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: aips2-request@nrao.edu.
//# Postal address: AIPS++ Project Office
//# National Radio Astronomy Observatory
//# 520 Edgemont Road
//# Charlottesville, VA 22903-2475 USA
//#
//# $Id$
#ifndef CASA_MMAPFDIO_H
#define CASA_MMAPFDIO_H
//# Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/IO/FiledesIO.h>
#include <casacore/casa/OS/RegularFile.h>
namespace casacore
{
// <summary>
// Memory-mapped IO on a file.
// </summary>
// <synopsis>
// Memory-mapped IO lets the OS take care of caching file segments.
// This is particularly useful for the Tiled Storage Manager which keeps a
// cache of tiles. When using memory-mapped IO it does not need to do that
// anymore.
//
// On 32-bit systems its use is limited because for large files the 4 GB
// memory space is insufficient. However, for 64-bit systems the memory
// space is large enough to make use of it.
//
// In the general case there is direct access to the mapped file space.
// The read and write methods copies the data into/from a buffer.
// However, to avoid the copying it is possible to get a direct pointer
// to the mapped data. This should be used with care, because writing to
// it will cause a segmentation if the file is readonly. If the file is
// writable, writing into the mapped data segment means changing the file
// contents.
// </synopsis>
class MMapfdIO: public FiledesIO
{
public:
// Default constructor.
// A file can be memory-mapped using the map function.
MMapfdIO();
// Map the given file descriptor entirely into memory with read access.
// The map has also write access if the file is opened for write.
// The file name is only used in possible error messages.
MMapfdIO (int fd, const String& fileName);
// Destructor.
// If needed, it will flush and unmap the file, but not close it.
~MMapfdIO();
// Map the given file descriptor entirely into memory with read access.
// The map has also write access if the file is opened for write.
// An exception is thrown if a file descriptor was already attached.
// The file name is only used in possible error messages.
void map (int fd, const String& fileName);
// Map or remap the entire file.
// Remapping is needed if the file has grown elsewhere.
void mapFile();
// Flush changed mapped data to the file.
// Nothing is done if the file is readonly.
void flush();
// Write the number of bytes from the seek position on.
// The file will be extended and remapped if writing beyond end-of-file.
// In that case possible pointers obtained using <src>getXXPointer</src>
// are not valid anymore.
virtual void write (Int64 size, const void* buf);
// Read <src>size</src> bytes from the File. Returns the number of bytes
// actually read. Will throw an exception (AipsError) if the requested
// number of bytes could not be read unless throwException is set to
// False. Will always throw an exception if the file is not readable or
// the system call returns an undocumented value.
virtual Int64 read (Int64 size, void* buf, Bool throwException=True);
// Get a read or write pointer to the given position in the mapped file.
// An exception is thrown if beyond end-of-file or it not writable.
// These functions should be used with care. If the pointer is used to
// access data beyond the file size, a segmentation fault will occur.
// So it means that the write pointer can only be used to update the file,
// not to extend it. The <src>seek</src> and <src>write</src> functions
// should be used to extend a file.
// <group>
const void* getReadPointer (Int64 offset) const;
void* getWritePointer (Int64 offset);
// </group>
// Get the file size.
Int64 getFileSize() const
{ return itsFileSize; }
protected:
// Reset the position pointer to the given value. It returns the
// new position.
virtual Int64 doSeek (Int64 offset, ByteIO::SeekOption);
// Unmap the file.
void unmapFile();
private:
// Forbid copy constructor and assignment
// <group>
MMapfdIO (const MMapfdIO&);
MMapfdIO& operator= (const MMapfdIO&);
// </group>
Int64 itsFileSize; //# File size
Int64 itsPosition; //# Current seek position
char* itsPtr; //# Pointer to memory map
Bool itsIsWritable;
};
} // end namespace
#endif
|