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casacore::MMapfdIO Class Reference

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

#include <MMapfdIO.h>

Inheritance diagram for casacore::MMapfdIO:
casacore::FiledesIO casacore::ByteIO casacore::MMapIO

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...
 
ByteIOoperator= (const ByteIO &byteIO)
 

Private Member Functions

 MMapfdIO (const MMapfdIO &)
 Forbid copy constructor and assignment. More...
 
MMapfdIOoperator= (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: