*** UNIX MANUAL PAGE BROWSER ***

mpool(3) Library Functions Manual mpool(3) NAME mpool, MPOOL, mpool_open, mpool_filter, mpool_new, mpool_get, mpool_put, mpool_sync, mpool_close - shared memory buffer pool SYNOPSIS #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); DESCRIPTION The routines are the library interface that provides page-oriented buffer management of files. The buffers may be shared between processes. The 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 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 point in time. This value is not relative to the number of processes that 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 spec- ified, 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 func- tions 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 argu- ments. If a new page can be allocated, a pointer to the page is re- turned and the page number is stored into the pgnoaddr address. Other- wise, NULL is returned and errno is set. The function mpool_get 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 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 The page has been modified and needs to be written to the back- ing 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 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. 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). RELATED INFORMATION dbopen(3), btree(3), hash(3), recno(3) delim off mpool(3)