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MMapfdIO.h
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//# 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: casa-feedback@nrao.edu.
//# Postal address: AIPS++ Project Office
//# National Radio Astronomy Observatory
//# 520 Edgemont Road
//# Charlottesville, VA 22903-2475 USA
#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();
// Forbid copy constructor and assignment
// <group>
MMapfdIO (const MMapfdIO&) = delete;
MMapfdIO& operator= (const MMapfdIO&) = delete;
// </group>
// 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:
Int64 itsFileSize; //# File size
Int64 itsPosition; //# Current seek position
char* itsPtr; //# Pointer to memory map
Bool itsIsWritable;
};
} // end namespace
#endif
casacore::ByteIO::SeekOption
SeekOption
Define the possible seek options.
Definition ByteIO.h:80
casacore::FiledesIO::fd
int fd() const
Get the file descriptor.
Definition FiledesIO.h:164
casacore::FiledesIO::FiledesIO
FiledesIO()
Default constructor.
casacore::FiledesIO::fileName
virtual String fileName() const
Get the file name of the file attached.
casacore::MMapfdIO::read
virtual Int64 read(Int64 size, void *buf, Bool throwException=True)
Read size bytes from the File.
casacore::MMapfdIO::getFileSize
Int64 getFileSize() const
Get the file size.
Definition MMapfdIO.h:123
casacore::MMapfdIO::MMapfdIO
MMapfdIO(int fd, const String &fileName)
Map the given file descriptor entirely into memory with read access.
casacore::MMapfdIO::write
virtual void write(Int64 size, const void *buf)
Write the number of bytes from the seek position on.
casacore::MMapfdIO::itsPosition
Int64 itsPosition
Definition MMapfdIO.h:136
casacore::MMapfdIO::getReadPointer
const void * getReadPointer(Int64 offset) const
Get a read or write pointer to the given position in the mapped file.
casacore::MMapfdIO::map
void map(int fd, const String &fileName)
Map the given file descriptor entirely into memory with read access.
casacore::MMapfdIO::MMapfdIO
MMapfdIO()
Default constructor.
casacore::MMapfdIO::operator=
MMapfdIO & operator=(const MMapfdIO &)=delete
casacore::MMapfdIO::unmapFile
void unmapFile()
Unmap the file.
casacore::MMapfdIO::~MMapfdIO
~MMapfdIO()
Destructor.
casacore::MMapfdIO::doSeek
virtual Int64 doSeek(Int64 offset, ByteIO::SeekOption)
Reset the position pointer to the given value.
casacore::MMapfdIO::itsPtr
char * itsPtr
Definition MMapfdIO.h:137
casacore::MMapfdIO::flush
void flush()
Flush changed mapped data to the file.
casacore::MMapfdIO::itsIsWritable
Bool itsIsWritable
Definition MMapfdIO.h:138
casacore::MMapfdIO::MMapfdIO
MMapfdIO(const MMapfdIO &)=delete
Forbid copy constructor and assignment.
casacore::MMapfdIO::mapFile
void mapFile()
Map or remap the entire file.
casacore::MMapfdIO::itsFileSize
Int64 itsFileSize
Definition MMapfdIO.h:135
casacore::MMapfdIO::getWritePointer
void * getWritePointer(Int64 offset)
casacore::String
String: the storage and methods of handling collections of characters.
Definition String.h:223
casacore
this file contains all the compiler specific defines
Definition mainpage.dox:28
casacore::offset
int offset(int, int) const
compute a linear offset from array indicies
casacore::Int64
long long Int64
Define the extra non-standard types used by Casacore (like proposed uSize, Size).
Definition aipsxtype.h:36
casacore::Bool
bool Bool
Define the standard types used by Casacore.
Definition aipstype.h:40
casacore::size
size_t size() const
Definition Block.h:557
casacore::True
const Bool True
Definition aipstype.h:41