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NetBSD 6.1.5 - man page for mpool_new (netbsd section 3)

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MPOOL(3)			   BSD Library Functions Manual 			 MPOOL(3)

NAME
     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
     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 descrip-
     tor 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 writ-
     ten.

     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 frees 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 spec-
     ified 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					December 16, 2010				      BSD
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