NAME
mpool —
shared memory buffer pool
SYNOPSIS
#include <db.h>
#include <mpool.h>
MPOOL *
mpool_open(void
*key, int fd,
pgno_t pagesize,
pgno_t maxcache);
void
mpool_filter(MPOOL *mp,
void (*pgin)(void *, pgno_t, void *),
void (*pgout)(void *, pgno_t, void *),
void *pgcookie);
void *
mpool_new(MPOOL
*mp, pgno_t
*pgnoaddr);
void *
mpool_get(MPOOL
*mp, pgno_t pgno,
u_int flags);
int
mpool_put(MPOOL
*mp, void *pgaddr,
u_int flags);
int
mpool_sync(MPOOL
*mp);
int
mpool_close(MPOOL
*mp);
DESCRIPTION
The mpool library interface is intended to
provide page oriented buffer management of files.
The
mpool_open()
function initializes a memory pool. The key argument
is currently ignored. The fd argument is a file
descriptor for the underlying file, which must be seekable.
The pagesize argument is the size, in bytes, of the pages into which the file is broken up. The maxcache argument is the maximum number of pages from the underlying file to cache at any one time. This value is not relative to the number of processes which share a file's buffers, but will be the largest value specified by any of the processes sharing the file.
The
mpool_filter()
function is intended to make transparent input and output processing of the
pages possible. If the pgin function is specified, it
is called each time a buffer is read into the memory pool from the backing
file. If the pgout function is specified, it is called
each time a buffer is written into the backing file. Both functions are
called with the pgcookie pointer, the page number and
a pointer to the page to being read or written.
The
mpool_new()
function takes an MPOOL pointer and an address as
arguments. If a new page can be allocated, a pointer to the page is returned
and the page number is stored into the pgnoaddr
address. Otherwise, NULL is returned and
errno is set.
The
mpool_get()
function takes a MPOOL pointer and a page number as
arguments. If the page exists, a pointer to the page is returned. Otherwise,
NULL is returned and errno is
set. The flags argument is not currently used.
The
mpool_put()
function unpins the page referenced by pgaddr. The
pgaddr argument must be an address previously returned
by mpool_get() or
mpool_new(). The flags
argument is specified by
or'ing any of
the following values:
MPOOL_DIRTY- The page has been modified and needs to be written to the backing file.
The
mpool_put()
function returns 0 on success and -1 if an error occurs.
The
mpool_sync()
function writes all modified pages associated with the
MPOOL pointer to the backing file. The
mpool_sync() function returns 0 on success and -1 if
an error occurs.
The
mpool_close()
function free's up any allocated memory associated with the memory pool
cookie. Modified pages are
not written
to the backing file. The mpool_close() function
returns 0 on success and -1 if an error occurs.
ERRORS
The mpool_open() function may fail and set
errno for any of the errors specified for the library
routine malloc(3).
The mpool_get() function may fail and set
errno for the following:
- [
EINVAL] - The requested record does not exist.
The mpool_new() and
mpool_get() functions may fail and set
errno for any of the errors specified for the library
routines read(2), write(2), and malloc(3).
The mpool_sync() function may fail and set
errno for any of the errors specified for the library
routine write(2).
The mpool_close() function may fail and
set errno for any of the errors specified for the
library routine free(3).