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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 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 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