IO_module

Basic classes and global functions for IO and object persistency. More...

Modules
	IO_module_internal_classes
	Internal IO_module classes and functions.

Classes
class	casacore::AipsIO
	AipsIO is the object persistency mechanism of Casacore. More...
struct	casacore::AipsIOCarray_global_functions_AipsIOCarray
	Templated functions to get/put a C-style array from/into AipsIO. More...
struct	casacore::ArrayIO_global_functions_Array_IO
	Input/output operators for Arrays. More...
struct	casacore::ArrayIO_global_functions_Array_binary_IO
	Global functions to read/write binary arrays from/to a file. More...
class	casacore::BaseSinkSource
	Shared base class for ByteSink and ByteSource. More...
class	casacore::BucketBuffered
	Use buffered file IO for buckets in a part of a file. More...
struct	casacore::BucketCache_global_functions_BucketCache_CallBack
	Define the type of the static read and write function. More...
class	casacore::BucketCache
	Cache for buckets in a part of a file. More...
class	casacore::BucketMapped
	Use file mapping for buckets in a part of a file. More...
class	casacore::ByteIO
	Abstract base class for IO on a byte stream. More...
class	casacore::ByteSink
	Class for write-only access to data in a given format. More...
class	casacore::ByteSinkSource
	Class for read/write access to data in a given format. More...
class	casacore::ByteSource
	Class for read-only access to data in a given format. More...
class	casacore::CanonicalIO
	Class for IO in canonical format. More...
class	casacore::ConversionIO
	Class for IO in a converted format. More...
class	casacore::FilebufIO
	Class for buffered IO on a file. More...
class	casacore::FiledesIO
	Class for unbuffered IO on a file. More...
class	casacore::FileLocker
	Class to handle file locking. More...
class	casacore::LECanonicalIO
	Class for IO in little endian canonical format. More...
class	casacore::LockFile
	Class to handle file locking and synchronization. More...
class	casacore::MemoryIO
	Class for IO to a memory buffer. More...
class	casacore::MFFileIO
	Class for IO on a virtual file in a MultiFileBase. More...
class	casacore::MMapfdIO
	Memory-mapped IO on a file. More...
class	casacore::MMapIO
	Memory-mapped IO on a file. More...
class	casacore::MultiFile
	Class to combine multiple files in a single one. More...
struct	casacore::MultiFileBuffer
	Helper class for MultiFileInfo holding a data buffer. More...
class	casacore::MultiFileBase
	Abstract base class to combine multiple files in a single one. More...
class	casacore::MultiHDF5
	Class to combine multiple files in a single HDF5 file. More...
class	casacore::RawIO
	Class for IO in local format. More...
class	casacore::RegularFileIO
	Class for IO on a regular file. More...
class	casacore::StreamIO
	Class for IO on connection oriented socket. More...
class	casacore::TapeIO
	Class for IO on a tape device. More...
class	casacore::TypeIO
	Abstract base class for IO of data in a type-dependent format. More...

Detailed Description

Basic classes and global functions for IO and object persistency.

See below for an overview of the classes in this module.

Review Status

Reviewed By:

UNKNOWN

Date Reviewed:

before2004/08/25

Synopsis

This module provides the basic IO functionality for the Casacore classes. There are two IO mechanisms:

1. Class AipsIO provides the object persistency mechanism. The templated global functions in AipsIOCarray.h form a little layer upon AipsIO. They provide the means to put or get a C-style array of any type.
2. Class ByteSinkSource and its ancestors provide a general IO mechanism.

Both use the underlying IO framework which define where and how the data are written. The how-part is defined by classes derived from TypeIO as shown in the UML diagram. There are three such classes:

1. CanonicalIO reads/writes data in canonical (machine-independent) format. This should be used when data are meant to be exportable. It uses the conversion functions in class

   CanonicalConversion .

2. RawIO reads/writes data in native (machine-dependent) format. This can be used when data are not exported.
3. ConversionIO reads/writes in an external format as defined at construction time. This can be used when the external format can be one of several (e.g. VAX or IBM for a WSRT archive tape). In this way the format has to be defined only once and thereafter is it handled correctly by the polymorphism mechanism.

The where-part is defined by classes derived from ByteIO as shown in the UML diagram. There are a few such classes:

1. RegularFileIO uses a regular file to hold the data. Internally it uses FilebufIO (see below). It can handle files > 2 GB.
2. FilebufIO does the IO in a buffered way similar to the stdio system. However, it does not use stdio because that gave problems when doing concurrent access from multiple processes. It can handle files > 2 GB.
3. FiledesIO uses the UNIX IO-functions like open, read to do IO directly. It does not use an internal buffer. Instead it always does physical IO. It is meant for IO operations where large chunks of a file are accessed and for IO on sockets, pipes, etc.. It can handle files > 2 GB.
4. StreamIO for IO on a socket.
5. TapeIO for IO on a tape device.
6. MemoryIO uses a (possibly expandable) buffer in memory to hold the data.
7. MMapIO uses memory-mapped IO. Be careful to use this on 32-bit machines, because its address space is too small to handle a file of a few GBytes.
8. MFFileIO uses a virtual file in a MultiFile container file. MultiFile is meant to combine multiple files in a single physical file to reduce the number of files used by the Casacore table system.

The IO framework is easily expandable. One can for instance think of a class AsciiIO derived from TypeIO to hold data in ASCII format. A class RemoteTapeIO could be developed for IO on a tape device on another node.