NAME
MappedFile - Create and map a disk file into memory. Map a named disk file into memory.
SYNOPSIS
#include <file.h>
Inherits RandomFile.
Public Methods
MappedFile (const char *fname, Access mode)
Open a file for mapping. MappedFile (const char *fname, pos_t offset, size_t size, Access mode)
Map a portion or all of a specified file in the specified shared memory access mode. virtual ~MappedFile ()
Release a mapped section of memory associated with a file. void sync (void)
Synchronize the contents of the mapped portion of memory with the disk file and wait for completion. void sync (char *address, size_t len)
Synchronize a segment of memory mapped from a segment fetch. void update (size_t offset=0, size_t len=0)
Map a portion of the memory mapped from the file back to the file and do not wait for completion. void update (char *address, size_t len)
Update a mapped region back to disk as specified by address and length. void release (char *address, size_t len)
Release (unmap) a memory segment. char * fetch (size_t offset=0)
Fetch a pointer to an offset within the memory mapped portion of the disk file. char * fetch (off_t pos, size_t len)
Fetch and map a portion of a disk file to a logical memory block.
DETAILED DESCRIPTION
Create and map a disk file into memory. Map a named disk file into memory.
This portable class works under both Posix via mmap and under the win32 API. A mapped file can be referenced directly by it's memory segment. One can map and unmap portions of a file on demand, and update changed memory pages mapped from files immediately through sync().
Author: David Sugar <[email protected]>
Todo:
implement in win32
CONSTRUCTOR & DESTRUCTOR DOCUMENTATION
MappedFile::MappedFile (const char * fname, Access mode)
Open a file for mapping.
More than one segment of a file may be mapped into seperate regions of memory.
Parameters:
- fname
-
file name to access for mapping.
- mode
-
access mode to map file.
MappedFile::MappedFile (const char * fname, pos_t offset, size_t size, Access mode)
Map a portion or all of a specified file in the specified shared memory access mode.
Valid mapping modes include mappedRead, mappedWrite, and mappedReadWrite.
Parameters:
- fname
-
pathname of file to map into memory.
- offset
-
from start of file to begin mapping in bytes.
- size
-
of mapped area in bytes.
- mode
-
to map file.
virtual MappedFile::~MappedFile () [virtual]
Release a mapped section of memory associated with a file.
The mapped area is updated back to disk.
MEMBER FUNCTION DOCUMENTATION
char* MappedFile::fetch (off_t pos, size_t len)
Fetch and map a portion of a disk file to a logical memory block.
Returns: pointer to memory segment.
Parameters:
- pos
-
offset of file segment to map.
- len
-
size of memory segment to map.
char* MappedFile::fetch (size_t offset = 0) [inline]
Fetch a pointer to an offset within the memory mapped portion of the disk file.
This really is used for convience of matching operations between Update and Fetch, as one could simply have accessed the base pointer where the file was mapped directly.
Parameters:
- offset
-
from start of mapped memory.
void MappedFile::release (char * address, size_t len)
Release (unmap) a memory segment.
Parameters:
- address
-
address of memory segment to release.
- len
-
length of memory segment to release.
void MappedFile::sync (char * address, size_t len)
Synchronize a segment of memory mapped from a segment fetch.
Parameters:
- address
-
memory address to update.
- len
-
size of segment.
void MappedFile::sync (void) [inline]
Synchronize the contents of the mapped portion of memory with the disk file and wait for completion.
This assures the memory mapped from the file is written back.
void MappedFile::update (char * address, size_t len)
Update a mapped region back to disk as specified by address and length.
Parameters:
- address
-
address of segment.
- len
-
length of segment.
void MappedFile::update (size_t offset = 0, size_t len = 0)
Map a portion of the memory mapped from the file back to the file and do not wait for completion.
This is useful when mapping a database file and updating a single record.
Parameters:
- offset
-
offset into the mapped region of memory.
- len
-
length of partial region (example, record length).
AUTHOR
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