MPOOL(3) Library Functions Manual MPOOL(3)

mpool — shared memory buffer pool

#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);

The mpool library interface is intended to provide page oriented buffer management of files.

The () 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 () 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 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 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 () 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 'ing any of the following values:

The page has been modified and needs to be written to the backing file.

The () function returns 0 on success and -1 if an error occurs.

The () 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 () function free's up any allocated memory associated with the memory pool cookie. Modified pages are written to the backing file. The mpool_close() function 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:

[]
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).

btree(3), dbopen(3), hash(3), recno(3)

June 4, 1993 Mac OS X 12