MPOOL(3)	       UNIX System V (June 4, 1993)	      MPOOL(3)



     NAME    [Toc]    [Back]
	  mpool	- shared memory	buffer pool

     SYNOPSIS    [Toc]    [Back]
	  #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    [Toc]    [Back]
	  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.




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     MPOOL(3)	       UNIX System V (June 4, 1993)	      MPOOL(3)



	  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	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 free's 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    [Toc]    [Back]
	  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).



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     MPOOL(3)	       UNIX System V (June 4, 1993)	      MPOOL(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    [Toc]    [Back]
	  dbopen(3), btree(3), hash(3),	recno(3)















































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