mpool


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, unsigned int flags);

       int mpool_put(MPOOL *mp, void *pgaddr, unsigned int flags);

       int mpool_sync(MPOOL *mp);

       int mpool_close(MPOOL *mp);

DESCRIPTION
       Note  well:  This  page documents interfaces provided in glibc up until
       version 2.1.  Since version 2.2, glibc no longer provides these  inter-
       faces.   Probably,  you  are looking for the APIs provided by the libdb
       library instead.

       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 called with the pgcookie  pointer,  the  page  number  and  a
       pointer to the page to being read or written.

       The flag value is specified by ORing 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).

CONFORMING TO
       Not in POSIX.1-2001.  Present on the BSDs.

SEE ALSO
       btree(3), dbopen(3), hash(3), recno(3)

COLOPHON
       This page is part of release 3.54 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



4.4 Berkeley Distribution         2012-04-26                          MPOOL(3)
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