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MPOOL(3)                   Library Functions Manual                   MPOOL(3)

NAME
     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
     mpool is the library interface intended to provide page oriented buffer
     management of files.  The buffers may be shared between processes.

     The function mpool_open() 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 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 function mpool_new() 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 mpool_get() 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 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 backing 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).

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

NetBSD 10.99                   December 16, 2010                  NetBSD 10.99