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mpool(3)							      mpool(3)

NAME
       mpool,	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
       The mpool routines are the library interface  that  provides  page-ori‐
       ented  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 point in time. This
       value is not relative to the number of processes that  share  a	file's
       buffers,	 but  will  be	the largest value specified by any of the pro‐
       cesses sharing the file.

       The function mpool_filter() 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 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
       arguments. If the page exists, a pointer to the page is returned.  Oth‐
       erwise,	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 option value is specified by ORing any of the following values: The
       page has been modified and needs to be written to the backing file.

       The  function  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. It returns 0 on success and -1 if an
       error occurs.

       The function mpool_close() frees up  any	 allocated  memory  associated
       with  the  memory  pool	cookie.	 Modified pages are not written to the
       backing file. The 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:  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
       dbopen(3), btree(3), hash(3), recno(3)

								      mpool(3)
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