paging

Documentation

Overview

Package paging contains functions and constants necessary for paging of records.

NOTE: Operations in this code are expected to either fail completely or succeed.
Errors in the middle of an operation may leave the datastructures in an
inconsistent state.

PageCursor

PageCursor is a pointer into a PagedStorageFile and can be used to traverse a linked list of pages (see also PagedStorageFileHeader which stores the entry points).

PagedStorageFile

PagedStorageFile is a wrapper object for a StorageFile which views the file records as a linked list of pages.

PagedStorageFileHeader

PagedStorageFileHeader is a wrapper object for the header record of a StorageFile. The header record stores information about linked lists and root values.

Index

• Constants
• Variables
• func CountPages(pager *PagedStorageFile, pagetype int16) (int, error)
• type PageCursor
  • func NewPageCursor(psf *PagedStorageFile, ptype int16, current uint64) *PageCursor
  • func (pc *PageCursor) Current() uint64
  • func (pc *PageCursor) Next() (uint64, error)
  • func (pc *PageCursor) Prev() (uint64, error)
• type PagedStorageFile
  • func NewPagedStorageFile(storagefile *file.StorageFile) (*PagedStorageFile, error)
  • func (psf *PagedStorageFile) AllocatePage(pagetype int16) (uint64, error)
  • func (psf *PagedStorageFile) Close() error
  • func (psf *PagedStorageFile) First(pagetype int16) uint64
  • func (psf *PagedStorageFile) Flush() error
  • func (psf *PagedStorageFile) FreePage(id uint64) error
  • func (psf *PagedStorageFile) Header() *PagedStorageFileHeader
  • func (psf *PagedStorageFile) Last(pagetype int16) uint64
  • func (psf *PagedStorageFile) Next(id uint64) (uint64, error)
  • func (psf *PagedStorageFile) Prev(id uint64) (uint64, error)
  • func (psf *PagedStorageFile) Rollback() error
  • func (psf *PagedStorageFile) StorageFile() *file.StorageFile
• type PagedStorageFileHeader
  • func NewPagedStorageFileHeader(record *file.Record, isnew bool) *PagedStorageFileHeader
  • func (psfh *PagedStorageFileHeader) CheckMagic()
  • func (psfh *PagedStorageFileHeader) FirstListElement(list int16) uint64
  • func (psfh *PagedStorageFileHeader) LastListElement(list int16) uint64
  • func (psfh *PagedStorageFileHeader) Root(root int) uint64
  • func (psfh *PagedStorageFileHeader) Roots() int
  • func (psfh *PagedStorageFileHeader) SetFirstListElement(list int16, val uint64)
  • func (psfh *PagedStorageFileHeader) SetLastListElement(list int16, val uint64)
  • func (psfh *PagedStorageFileHeader) SetRoot(root int, val uint64)

Constants

const OffsetLists = 2

OffsetLists is the offset for list entries in this header

const OffsetRoots = OffsetLists + (2 * TotalLists * file.SizeLong)

OffsetRoots is the number of lists which can be stored in this header

const PageHeader = 0x1980

PageHeader is the magic number to identify page headers

const TotalLists = 5

TotalLists is the number of lists which can be stored in this header

Variables

var (
	ErrFreePage = errors.New("Cannot allocate/free a free page")
	ErrHeader   = errors.New("Cannot modify header record")
)

Common paged storage file related errors

Functions

func CountPages

func CountPages(pager *PagedStorageFile, pagetype int16) (int, error)

CountPages counts the number of pages of a certain type of a given PagedStorageFile.

Types

type PageCursor

type PageCursor struct {
	// contains filtered or unexported fields
}

PageCursor data structure

func NewPageCursor

func NewPageCursor(psf *PagedStorageFile, ptype int16, current uint64) *PageCursor

NewPageCursor creates a new cursor object which can be used to traverse a set of pages.

func (*PageCursor) Current

func (pc *PageCursor) Current() uint64

Current gets the page this cursor currently points at.

func (*PageCursor) Next

func (pc *PageCursor) Next() (uint64, error)

Next moves the PageCursor to the next page and returns it.

func (*PageCursor) Prev

func (pc *PageCursor) Prev() (uint64, error)

Prev moves the PageCursor to the previous page and returns it.

type PagedStorageFile

type PagedStorageFile struct {
	// contains filtered or unexported fields
}

PagedStorageFile data structure

func NewPagedStorageFile

func NewPagedStorageFile(storagefile *file.StorageFile) (*PagedStorageFile, error)

NewPagedStorageFile wraps a given StorageFile and returns a PagedStorageFile.

func (*PagedStorageFile) AllocatePage

func (psf *PagedStorageFile) AllocatePage(pagetype int16) (uint64, error)

AllocatePage allocates a new page of a specific type.

func (*PagedStorageFile) Close

func (psf *PagedStorageFile) Close() error

Close commits all data and closes all physical files.

func (*PagedStorageFile) First

func (psf *PagedStorageFile) First(pagetype int16) uint64

First returns the first page of a list of a given type.

func (*PagedStorageFile) Flush

func (psf *PagedStorageFile) Flush() error

Flush writes all pending data to disk.

func (*PagedStorageFile) FreePage

func (psf *PagedStorageFile) FreePage(id uint64) error

FreePage frees a given page and adds it to the free list.

func (*PagedStorageFile) Header

func (psf *PagedStorageFile) Header() *PagedStorageFileHeader

Header returns the header object of this PagedStorageFile.

func (*PagedStorageFile) Last

func (psf *PagedStorageFile) Last(pagetype int16) uint64

Last returns the first page of a list of a given type.

func (*PagedStorageFile) Next

func (psf *PagedStorageFile) Next(id uint64) (uint64, error)

Next returns the next page of a given page in a list.

func (*PagedStorageFile) Prev

func (psf *PagedStorageFile) Prev(id uint64) (uint64, error)

Prev returns the previous page of a given page in a list.

func (*PagedStorageFile) Rollback

func (psf *PagedStorageFile) Rollback() error

Rollback discards all changes which were done after the last flush. The PageStorageFile object should be discarded if something goes wrong during a rollback operation.

func (*PagedStorageFile) StorageFile

func (psf *PagedStorageFile) StorageFile() *file.StorageFile

StorageFile returns the wrapped StorageFile.

type PagedStorageFileHeader

type PagedStorageFileHeader struct {
	// contains filtered or unexported fields
}

PagedStorageFileHeader data structure

func NewPagedStorageFileHeader

func NewPagedStorageFileHeader(record *file.Record, isnew bool) *PagedStorageFileHeader

NewPagedStorageFileHeader creates a new NewPagedStorageFileHeader.

func (*PagedStorageFileHeader) CheckMagic

func (psfh *PagedStorageFileHeader) CheckMagic()

CheckMagic checks the header magic value of this header.

func (*PagedStorageFileHeader) FirstListElement

func (psfh *PagedStorageFileHeader) FirstListElement(list int16) uint64

FirstListElement returns the first element of a list.

func (*PagedStorageFileHeader) LastListElement

func (psfh *PagedStorageFileHeader) LastListElement(list int16) uint64

LastListElement returns the last element of a list.

func (*PagedStorageFileHeader) Root

func (psfh *PagedStorageFileHeader) Root(root int) uint64

Root returns a root value.

func (*PagedStorageFileHeader) Roots

func (psfh *PagedStorageFileHeader) Roots() int

Roots returns the number of possible root values which can be set.

func (*PagedStorageFileHeader) SetFirstListElement

func (psfh *PagedStorageFileHeader) SetFirstListElement(list int16, val uint64)

SetFirstListElement sets the first element of a list.

func (*PagedStorageFileHeader) SetLastListElement

func (psfh *PagedStorageFileHeader) SetLastListElement(list int16, val uint64)

SetLastListElement sets the last element of a list.

func (*PagedStorageFileHeader) SetRoot

func (psfh *PagedStorageFileHeader) SetRoot(root int, val uint64)

SetRoot sets a root value.