MPOOL(3) BSD Library Functions Manual MPOOL(3)NAME
mpool — shared memory buffer pool
LIBRARY
Standard C Library (libc, -lc)
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 buffers may be shared between processes.
The mpool_open() function 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 pro‐
cesses 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 speci‐
fied, 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 argu‐
ments. 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 argu‐
ments. If the page exists, a pointer to the page is returned. Other‐
wise, NULL is returned and errno is set. The flags argument is not cur‐
rently 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 fol‐
lowing 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 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).
SEE ALSObtree(3), dbopen(3), hash(3), recno(3)BSD June 4, 1993 BSD
