mpool man page on 4.4BSD

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MPOOL(3)							      MPOOL(3)

NAME
       mpool - 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 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  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
       returned and the page number is stored into the pgnoaddr address.  Oth‐
       erwise, 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 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
       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
       dbopen(3), btree(3), hash(3), recno(3)

4.4 Berkeley Distribution	 June 4, 1993			      MPOOL(3)
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