| NAME | SYNOPSIS | DESCRIPTION | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON | The Linux Programming Interface |
MPOOL(3) Linux Programmer's Manual MPOOL(3)
mpool - shared memory buffer pool
#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, unsigned int flags);
int mpool_put(MPOOL *mp, void *pgaddr, unsigned 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 an 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 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
The page has been modified and needs to be written to the backing file.
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 free's 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.
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 doesn't 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).
Not in POSIX.1-2001. Present on the BSDs.
btree(3), dbopen(3), hash(3), recno(3)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
4.4 Berkeley Distribution 1993-06-04 MPOOL(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface