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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, u_int flags);

     int
     mpool_delete(MPOOL	*mp, void *page);

     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 underly-
     ing 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 speci-
     fied, 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, an address, and a	set of
     flags 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	flags value is formed
     by	OR'ing the following values:

     MPOOL_PAGE_REQUEST
	     Allocate a	new page with a	specific page number.

     MPOOL_PAGE_NEXT
	     Allocate a	new page with the next page number.

     The function mpool_delete() deletes the specified page from a pool	and
     frees the page.  It takes an MPOOL	pointer	and a page as arguments.  The
     page must have been generated by mpool_new().

     The mpool_get() function 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 argument is specified
     by	or'ing any of the following values:

     MPOOL_IGNOREPIN
	     The page returned is not pinned; page will	otherwise be pinned on
	     return.

     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	fol-
     lowing 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.  Modified 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 routine 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 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)

BSD				 June 17, 2011				   BSD

NAME | SYNOPSIS | DESCRIPTION | ERRORS | SEE ALSO

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