ost::mappedfile(3)

NAME

ost::MappedFile - Create and map a disk file into memory.

SYNOPSIS

#include <file.h>
Inherits ost::RandomFile.
Public Member Functions
MappedFile (const char *fname, Access mode)
    Open a file for mapping.
MappedFile (const char *fname, Access mode, size_t size)
    Create if not exists, and map a file of specified size into memory.
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.
bool lock (void)
    Lock the currently mapped portion of a file.
void unlock (void)
    Unlock a locked mapped portion of a file.
size_t pageAligned (size_t size)
    Compute map size to aligned page boundry.

Detailed Description

Create and map a 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 <dyfet@ostel.com> Map a named disk file into memory.

Constructor & Destructor Documentation

ost::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.
ost::MappedFile::MappedFile (const char * fname, Access mode, size_t size): Create if not exists, and map a file of specified size into memory.; Parameters:
fname file name to access for mapping.
mode access mode to map file.
size of file to map.
ost::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 ost::MappedFile::~MappedFile () [virtual]: Release a mapped section of memory associated with a file.; The mapped area is updated back to disk.

Member Function Documentation

void ost::MappedFile::sync (void): 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 ost::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 ost::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).
void ost::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 ost::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.
char* ost::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.
char* ost::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.
bool ost::MappedFile::lock (void): Lock the currently mapped portion of a file.; Returns:
true if pages are locked.
void ost::MappedFile::unlock (void): Unlock a locked mapped portion of a file.
size_t ost::MappedFile::pageAligned (size_t size): Compute map size to aligned page boundry.; Parameters:
size request.; Returns:
page aligned size.

Author

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