Index for Section 3

Alphabetical listing for M

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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-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 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 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 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 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).

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

Index for Section 3

Alphabetical listing for M

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