mpool(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON

MPOOL(3)                Linux Programmer's Manual               MPOOL(3)

NAME         top

       mpool - shared memory buffer pool

SYNOPSIS         top

       #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         top

       Note well: This page documents interfaces provided in glibc up
       until version 2.1.  Since version 2.2, glibc no longer provides
       these interfaces.  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 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 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 an 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 argument 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 ORing 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         top

       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         top

       Not in POSIX.1.  Present on the BSDs.

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.10 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

4.4 Berkeley Distribution      2017-09-15                       MPOOL(3)

Pages that refer to this page: btree(3)dbopen(3)hash(3)recno(3)