MPOOL(3) | Library Functions Manual | MPOOL(3) |
mpool
, mpool_open
,
mpool_filter
, mpool_new
,
mpool_get
, mpool_put
,
mpool_sync
, mpool_close
—
#include <db.h>
#include <mpool.h>
MPOOL *
mpool_open
(DBT
*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);
mpool
is the library interface intended to provide page
oriented buffer management of files. The buffers may be shared between
processes.
The function mpool_open
() initializes a
memory pool. The key argument is the byte string used
to negotiate between multiple processes wishing to share buffers. If the
file buffers are mapped in shared memory, all processes using the same key
will share the buffers. If key is
NULL
, the buffers are mapped into private memory.
The fd argument is a file descriptor for the
underlying file, which must be seekable. If key is
non-NULL
and matches a file
already being mapped, the fd argument is ignored.
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 function mpool_new
() 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 function mpool_get
() 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 parameter is not currently used.
The function mpool_put
() unpins the page
referenced by pgaddr. pgaddr
must be an address previously returned by
mpool_get
() or mpool_new
().
The flag value is specified by or'ing any of the following values:
MPOOL_DIRTY
mpool_put
() returns 0 on success and -1 if
an error occurs.
The function mpool_sync
() writes all
modified pages associated with the MPOOL pointer to the backing file.
mpool_sync
() returns 0 on success and -1 if an error
occurs.
The mpool_close
() function frees up any
allocated memory associated with the memory pool cookie. Modified pages are
not written to the backing file.
mpool_close
() returns 0 on success and -1 if an
error occurs.
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 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).
December 16, 2010 | NetBSD 9.0 |