MPOOL(3) BSD Library Functions Manual MPOOL(3)
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. Mod-ified Modified
ified 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 rou-tine routine
tine 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 rou-tine routine
tine write(2).
The mpool_close() function may fail and set errno for any of the errors specified for the library rou-tine routine
tine free(3).
SEE ALSO
btree(3), dbopen(3), hash(3), recno(3)
BSD June 4, 1993 BSD
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