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RedHat 9 (Linux i386) - man page for mpool (redhat section 3)

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 buf-
       fers 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  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
       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  speci-
       fied 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		    1993-06-04					 MPOOL(3)


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