NRAOCASA: casa::FilebufIO Class Reference

This class is a specialization of class ByteIO . This class is doing IO on a file in a buffered way to reduce the number of file accesses as much as possible. It is part of the entire IO framework. It can for instance be used to store data in canonical format in a file in an IO-efficient way
The buffer size is dynamic, so any time it can be set as needed.

It is also possible to construct a FilebufIO object from a file descriptor (e.g. for a pipe or socket). The constructor will determine automatically if the file is readable, writable and seekable.

Example

This example shows how FilebufIO can be used with an fd. It uses the fd for a regular file, which could be done in an easier way using class RegularFileIO . However, when using pipes or sockets, this would be the only way.

       // Get a file descriptor for the file.
       int fd = open ("file.name");
       // Use that as the source of AipsIO (which will also use CanonicalIO).
       FilebufIO fio (fd);
       AipsIO stream (&fio);
       // Read the data.
       Int vali;
       Bool valb;
       stream >> vali >> valb;

Motivation

The stdio package was used, but it proved to be very slow on Solaris. After a seek the buffer was refreshed, which increased the number of file accesses enormously. Also the interaction between reads and writes in stdio required speial care.

Definition at line 94 of file FilebufIO.h.


Public Member Functions
	FilebufIO ()
	Default constructor.
	FilebufIO (int fd, uInt bufferSize=16384)
	Construct from the given file descriptor.
void	attach (int fd, uInt bufferSize=16384)
	Attach to the given file descriptor.
	~FilebufIO ()
	The destructor closes the file when it was owned and opened and not closed yet.
virtual void	write (uInt size, const void *buf)
	Write the number of bytes.
virtual Int	read (uInt size, void *buf, Bool throwException=True)
	Read `size` bytes from the File.
void	flush ()
	Flush the current buffer.
void	resync ()
	Resync the file (i.e.
virtual Int64	length ()
	Get the length of the byte stream.
virtual Bool	isReadable () const
	Is the IO stream readable?
virtual Bool	isWritable () const
	Is the IO stream writable?
virtual Bool	isSeekable () const
	Is the IO stream seekable?
virtual String	fileName () const
	Get the file name of the file attached.
uInt	bufferSize () const
	Get the buffer size.
Protected Member Functions
void	detach (Bool closeFile=False)
	Detach the FILE.
void	fillRWFlags (int fd)
	Determine if the file descriptor is readable and/or writable.
void	fillSeekable ()
	Determine if the file is seekable.
virtual Int64	doSeek (Int64 offset, ByteIO::SeekOption)
	Reset the position pointer to the given value.
void	setBuffer (uInt bufSize)
	Set a new buffer size.
void	writeBuffer (Int64 offset, const char *buf, Int size)
	Write a buffer of given length into the file at given offset.
uInt	readBuffer (Int64 offset, char *buf, uInt size, Bool throwException)
	Read a buffer of given length from the file at given offset.
void	writeBlock (uInt size, const char *buf)
	Write a block into the stream at the current offset.
uInt	readBlock (uInt size, char *buf, Bool throwException)
	Read a block from the stream at the current offset.
Private Member Functions
	FilebufIO (const FilebufIO &that)
	Copy constructor, should not be used.
FilebufIO &	operator= (const FilebufIO &that)
	Assignment, should not be used.
Private Attributes
Bool	itsSeekable
Bool	itsReadable
Bool	itsWritable
int	itsFile
uInt	itsBufSize
uInt	itsBufLen
char *	itsBuffer
Int64	itsBufOffset
Int64	itsOffset
Int64	itsSeekOffset
Bool	itsDirty

Constructor & Destructor Documentation

casa::FilebufIO::FilebufIO ( )

Default constructor.

A stream can be attached using the attach function.

casa::FilebufIO::FilebufIO	(	int	fd,
		uInt	bufferSize = `16384`
	)			`[explicit]`

Construct from the given file descriptor.

Note that the detach function can be told to close the file descriptor.

casa::FilebufIO::~FilebufIO ( )

The destructor closes the file when it was owned and opened and not closed yet.

casa::FilebufIO::FilebufIO ( const FilebufIO & that ) [private]

Copy constructor, should not be used.

Member Function Documentation

void casa::FilebufIO::attach	(	int	fd,
		uInt	bufferSize = `16384`
	)

Attach to the given file descriptor.

Note that the detach function can be told to close the file descriptor.

virtual void casa::FilebufIO::write	(	uInt	size,
		const void *	buf
	)			`[virtual]`

Write the number of bytes.

Implements casa::ByteIO.

virtual Int casa::FilebufIO::read	(	uInt	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.

Implements casa::ByteIO.

void casa::FilebufIO::flush ( )

Flush the current buffer.

void casa::FilebufIO::resync ( )

Resync the file (i.e.

empty the current buffer).

virtual Int64 casa::FilebufIO::length ( ) [virtual]

Get the length of the byte stream.

Implements casa::ByteIO.

virtual Bool casa::FilebufIO::isReadable ( ) const [virtual]

Is the IO stream readable?

Implements casa::ByteIO.