Index for Section 3

Alphabetical listing for M

Bottom of page

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 function mpool_filter() 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 option
  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.

  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:

  [EINVAL]
      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)

Index for Section 3

Alphabetical listing for M

Top of page