soma::AllocatorStrategy Class Reference

Determination of the allocation type depending of the buffer size to allocate and the disk format of data. More...

#include <soma-io/allocator/allocator.h>

Public Types
enum	DataAccess { InternalModif, ReadOnly, ReadWrite, NotOwner }
	Data access modes, they describe what you intend to do with data to be read. More...
enum	MappingMode {   Memory, MEM = Memory, MAP, CopyMap,   MAP_COPY = CopyMap, ReadOnlyMap, MAP_RO = ReadOnlyMap, ReadWriteMap,   MAP_RW = ReadWriteMap, Unallocated }

Static Public Member Functions
static MappingMode	mappingMode (DataAccess mode, offset_t buflen, const DataSource *datasource, bool isDiskformatOK, float usefactor=1)
	Determines optimal allocator for a data file. More...
static bool	isMMapCompatible (bool ascii, int byteorder, bool scalefactored=false, int border=0)
	helper function, tells if memory mapping is directly possible More...
static void	memSizes (offset_t &ram, offset_t &freeram, offset_t &swap)
	same as above but uses a Header attributed object More...
static AllocatorContext	allocator (MappingMode mode, carto::rc_ptr< DataSource > ds)
static const LowLevelAllocator &	lowLevelAllocator (MappingMode m)

Detailed Description

Determination of the allocation type depending of the buffer size to allocate and the disk format of data.

The optimal allocation mode depends on:

• what you intend to do with the data: read only, read / modify / rewrite to disk, read / modify internally but leave it unchanged on disk
• if data on disk is stored in the same format as the memory format (binary data, no byteswapping, no alignment mismatch, no scalefactor...)
• the size of data
• possibly the size of the system memory (total or currently available), but as it cannot be determined in a portable way, this information is likely not to be accessible on every system, so we use absolute threshold instead

Definition at line 150 of file allocator.h.

Member Enumeration Documentation

DataAccess

enum soma::AllocatorStrategy::DataAccess

Data access modes, they describe what you intend to do with data to be read.

Enumerator
InternalModif	Mode for internal modification. If memory mapping is enabled, it will be on a copy of the input file (MAP_COPY) because it needs to be writeable but must not modify the original file. It is the safest mode (but not the more efficient), so if you hesitate, take this one.
ReadOnly	Mode for read-only access.
ReadWrite	Mode for read/write access, the input file will be modified and needs read/write permissions.
NotOwner	This value is used for sub-volumes or fake volumes using data that are already allocated by another structure.

Definition at line 155 of file allocator.h.

MappingMode

enum soma::AllocatorStrategy::MappingMode

Enumerator
Memory
MEM
MAP
CopyMap
MAP_COPY
ReadOnlyMap
MAP_RO
ReadWriteMap
MAP_RW
Unallocated

Definition at line 173 of file allocator.h.

Member Function Documentation

allocator()

static AllocatorContext soma::AllocatorStrategy::allocator ( MappingMode  mode, carto::rc_ptr< DataSource >  ds  )

static

isMMapCompatible()

static bool soma::AllocatorStrategy::isMMapCompatible ( bool  ascii, int  byteorder, bool  scalefactored = false, int  border = 0  )

static

helper function, tells if memory mapping is directly possible

lowLevelAllocator()

static const LowLevelAllocator& soma::AllocatorStrategy::lowLevelAllocator ( MappingMode  m )

static

Referenced by soma::AllocatorContext::allocate().

mappingMode()

static MappingMode soma::AllocatorStrategy::mappingMode ( DataAccess  mode, offset_t  buflen, const DataSource *  datasource, bool  isDiskformatOK, float  usefactor = 1  )

static

Determines optimal allocator for a data file.

Parameters

mode	what you intend to do tith the data: read only, read/write or read/internally modify it. read/write mode is dangerous: it will allow modifying the original file.
buflen	size in bytes of the data to allocate
datasource	data source to map (file, buffer, stream, ...)
isDiskformatOK	true if the disk format is exactly the same as the internal memory format (allowing direct memory mapping)
usefactor	rate of usage you intend to do with the data, from 0 if you will only use a few bytes of it, to 1 if you intend to make intensive usage of all data. A small value will allow memory mapping on smaller files, and a higher value will avoid it.

Referenced by soma::AllocatorContext::allocate().

memSizes()

static void soma::AllocatorStrategy::memSizes ( offset_t &  ram, offset_t &  freeram, offset_t &  swap  )

static

same as above but uses a Header attributed object

Try to detect memory amounts and fills referenced params. Params are set to 0 if thezy cannor be determined.

Parameters

ram	physical RAM amount
freeram	free RAM amount
swap	free RAM+swap amount

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

• soma-io/allocator/allocator.h