FileAllocator Class Reference

Maintains memory blocks within a file. More...

#include <FileAllocator.h>

Public Member Functions
	FileAllocator ()
	Constructor/destructor check if attach/detach have been called. More...
	~FileAllocator ()
	Destructor checks if detach has been called.
bool	attach (FILE *f, FileOffset reserved_space, bool init)
	Must be invoked to attach (& initialize) a file. More...
FILE *	getFile () const
void	detach ()
	Must be called before destroying the FileAllocator and closing the file.
FileOffset	allocate (FileOffset num_bytes)
	Allocate a block with given size, returning a file offset (for fseek). More...
FileOffset	size () const
void	free (FileOffset offset)
	Release a file block (will be placed in free list). More...
bool	dump (int level=1, FILE *out=stdout)
	Show ASCII-type info about the file structure. More...

Static Public Attributes
static FileOffset	minimum_size
	To avoid allocating tiny areas, also to avoid splitting free blocks into pieces that are then too small to be ever useful, all memory regions are at least this big. More...
static FileOffset	file_size_increment
	Setting file_size_increment will cause the file size to jump in the given increments. More...

Detailed Description

Maintains memory blocks within a file.

The FileAllocator maintains the space in a given file by keeping track of allocated blocks. Sections can also be released, in which case they are placed in a free-list for future allocations.

Constructor & Destructor Documentation

FileAllocator::FileAllocator

(

)

Constructor/destructor check if attach/detach have been called.

We could have made these perform the attach/detach, but then the error reporting would have had to use exceptions which we'd like to avoid.

Member Function Documentation

FileOffset FileAllocator::allocate

(

FileOffset

num_bytes

)

Allocate a block with given size, returning a file offset (for fseek).

See Also

free()

Exceptions

GenericException

on error.

bool FileAllocator::attach	(	FILE *	f,
		FileOffset	reserved_space,
		bool	init
	)

Must be invoked to attach (& initialize) a file.

Can be invoked on an empty file with init=true, in thich case the reserved space and some FileAllocator header will be added to the file. Can also be invoked on an existing file (init=false or true) which was initialized by the FileAllocator, in which case the reserved_space has to match the value that was used when initializing the file!

init=true means this file is used for writing, and we are allowed to create a new file allocator header for an empty file.

Returns

true when an empty file was initialized. Otherwise, some weak tests are performed so see if this file does indeed contain a FileAllocator header, and false is returned.

Exceptions

GenericException

on error.

bool FileAllocator::dump	(	int	level = 1,
		FILE *	out = stdout
	)

Show ASCII-type info about the file structure.

This routines lists all the allocated and free blocks together with some other size information. It also performs some sanity checks. When called with level=0, it will only perform the tests and only report possible problems.

Should not throw exceptions but simply return false on errors.

Parameters

level	Level of verbosity.
out	When non-zero, it is used instead of stdout.

Returns true for 'OK'.

void FileAllocator::free

(

FileOffset

offset

)

Release a file block (will be placed in free list).

Parameters

offset

A file offset previously obtained from allocate()

Warning

It is an error to free space that wasn't allocated. There is no 100% dependable way to check this, but free() will perform some basic test and return false for inknown memory regions.

Exceptions

GenericException

on error.

FILE* FileAllocator::getFile

(

)

const

Returns

After attaching to a file, this returns the file.

FileOffset FileAllocator::size ( ) const

inline

Returns

Total size of file in bytes.

Member Data Documentation

FileOffset FileAllocator::file_size_increment

static

Setting file_size_increment will cause the file size to jump in the given increments.

FileOffset FileAllocator::minimum_size

static

To avoid allocating tiny areas, also to avoid splitting free blocks into pieces that are then too small to be ever useful, all memory regions are at least this big.

Meaning: Whenever you allocate less than minimum_size, you will get a block that's actually minimum_size.

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

• /home/malitsky/projects/epics-archiver/sourceforge/trunk/ea4-cpp/include/common/storage/FileAllocator.h