Memory-mapped IO on a file. More...

#include <MMapfdIO.h>

Inheritance diagram for casacore::MMapfdIO:

Public Member Functions
	MMapfdIO ()
	Default constructor. More...

	MMapfdIO (int fd, const String &fileName)
	Map the given file descriptor entirely into memory with read access. More...

	~MMapfdIO ()
	Destructor. More...

void	map (int fd, const String &fileName)
	Map the given file descriptor entirely into memory with read access. More...

void	mapFile ()
	Map or remap the entire file. More...

void	flush ()
	Flush changed mapped data to the file. More...

virtual void	write (Int64 size, const void *buf)
	Write the number of bytes from the seek position on. More...

virtual Int64	read (Int64 size, void *buf, Bool throwException=True)
	Read `size` bytes from the File. More...

const void *	getReadPointer (Int64 offset) const
	Get a read or write pointer to the given position in the mapped file. More...

void *	getWritePointer (Int64 offset)

Int64	getFileSize () const
	Get the file size. More...

Public Member Functions inherited from casacore::FiledesIO
	FiledesIO ()
	Default constructor. More...

	FiledesIO (int fd, const String &fileName=String())
	Construct from the given file descriptor. More...

void	attach (int fd, const String &fileName)
	Attach to the given file descriptor. More...

void	detach ()
	Detach from the file descriptor. More...

virtual	~FiledesIO ()
	The destructor detaches, but does not close the file. More...

virtual void	pwrite (Int64 size, Int64 offset, const void *buf)
	Write the number of bytes at offset from start of the file. More...

virtual Int64	pread (Int64 size, Int64 offset, void *buf, Bool throwException=True)
	Like read except reads from offset of the start of the file. More...

virtual Int64	length ()
	Get the length of the byte stream. More...

virtual Bool	isReadable () const
	Is the IO stream readable? More...

virtual Bool	isWritable () const
	Is the IO stream writable? More...

virtual Bool	isSeekable () const
	Is the IO stream seekable? More...

void	setWritable ()
	Set that the IO stream is writable. More...

virtual String	fileName () const
	Get the file name of the file attached. More...

virtual void	fsync ()
	Fsync the file (i.e. More...

Public Member Functions inherited from casacore::ByteIO
	ByteIO ()
	The constructor does nothing. More...

virtual	~ByteIO ()

virtual void	reopenRW ()
	Reopen the underlying IO stream for read/write access. More...

Int64	seek (Int offset, ByteIO::SeekOption=ByteIO::Begin)
	This function sets the position on the given offset. More...

Int64	seek (Int64 offset, ByteIO::SeekOption=ByteIO::Begin)

virtual void	resync ()
	Resync the file (i.e. More...

Protected Member Functions
virtual Int64	doSeek (Int64 offset, ByteIO::SeekOption)
	Reset the position pointer to the given value. More...

void	unmapFile ()
	Unmap the file. More...

Protected Member Functions inherited from casacore::FiledesIO
int	fd () const
	Get the file descriptor. More...

void	fillRWFlags (int fd)
	Determine if the file descriptor is readable and/or writable. More...

void	fillSeekable ()
	Determine if the file is seekable. More...

Protected Member Functions inherited from casacore::ByteIO
	ByteIO (const ByteIO &byteIO)
	Make copy constructor and assignment protected, so a user cannot use them (but a derived class can). More...

ByteIO &	operator= (const ByteIO &byteIO)

Private Member Functions
	MMapfdIO (const MMapfdIO &)
	Forbid copy constructor and assignment. More...

MMapfdIO &	operator= (const MMapfdIO &)

Private Attributes
Int64	itsFileSize

Int64	itsPosition

char *	itsPtr

Bool	itsIsWritable

Additional Inherited Members
Public Types inherited from casacore::ByteIO
enum	OpenOption { Old, Update, Append, New, NewNoReplace, Scratch, Delete }
	Define the possible ByteIO open options. More...

enum	SeekOption { Begin, Current, End }
	Define the possible seek options. More...

Static Public Member Functions inherited from casacore::FiledesIO
static int	create (const Char *name, int mode=0666)
	Some static convenience functions for file create/open/close. More...

static int	open (const Char *name, Bool writable=False, Bool throwExcp=True)

static void	close (int fd)

Detailed Description

Memory-mapped IO on a file.

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.

Definition at line 63 of file MMapfdIO.h.

Constructor & Destructor Documentation

casacore::MMapfdIO::MMapfdIO ( )

Default constructor.

A file can be memory-mapped using the map function.

casacore::MMapfdIO::MMapfdIO	(	int	fd,
		const String &	fileName
	)

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.

casacore::MMapfdIO::~MMapfdIO ( )

Destructor.

If needed, it will flush and unmap the file, but not close it.

casacore::MMapfdIO::MMapfdIO ( const MMapfdIO & )

private

Forbid copy constructor and assignment.

Member Function Documentation

virtual Int64 casacore::MMapfdIO::doSeek	(	Int64	offset,
		ByteIO::SeekOption
	)

protectedvirtual

Reset the position pointer to the given value.

It returns the new position.

Reimplemented from casacore::FiledesIO.

void casacore::MMapfdIO::flush ( )

virtual

Flush changed mapped data to the file.

Nothing is done if the file is readonly.

Reimplemented from casacore::ByteIO.

Int64 casacore::MMapfdIO::getFileSize ( ) const

inline

Get the file size.

Definition at line 119 of file MMapfdIO.h.

References itsFileSize.

const void* casacore::MMapfdIO::getReadPointer ( Int64 offset ) const

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 seek and write functions should be used to extend a file.

void* casacore::MMapfdIO::getWritePointer ( Int64 offset )

void casacore::MMapfdIO::map	(	int	fd,
		const String &	fileName
	)

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 casacore::MMapfdIO::mapFile ( )

Map or remap the entire file.

Remapping is needed if the file has grown elsewhere.

MMapfdIO& casacore::MMapfdIO::operator= ( const MMapfdIO & )

private

virtual Int64 casacore::MMapfdIO::read	(	Int64	size,
		void *	buf,
		Bool	throwException = `True`
	)

virtual

Read size 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.

Reimplemented from casacore::FiledesIO.

void casacore::MMapfdIO::unmapFile ( )

protected

Unmap the file.

virtual void casacore::MMapfdIO::write	(	Int64	size,
		const void *	buf
	)

virtual

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 getXXPointer are not valid anymore.

Reimplemented from casacore::FiledesIO.

Member Data Documentation

Int64 casacore::MMapfdIO::itsFileSize

private

Definition at line 137 of file MMapfdIO.h.

Referenced by getFileSize().

Bool casacore::MMapfdIO::itsIsWritable

private

Definition at line 140 of file MMapfdIO.h.

Int64 casacore::MMapfdIO::itsPosition

private

Definition at line 138 of file MMapfdIO.h.

char* casacore::MMapfdIO::itsPtr

private

Definition at line 139 of file MMapfdIO.h.

The documentation for this class was generated from the following file:

casa/casacore/casa/IO/MMapfdIO.h

Public Member Functions

Protected Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Synopsis

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation