NAME
mpool_open,
mpool_filter, mpool_new,
mpool_delete, mpool_get,
mpool_put, mpool_sync,
mpool_close —
shared memory buffer pool
SYNOPSIS
#include <db.h>
#include <mpool.h>
MPOOL *
mpool_open(void
*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, unsigned int
flags);
int
mpool_delete(MPOOL
*mp, void
*page);
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
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 being read or written.
The function
mpool_new()
takes an MPOOL pointer, an address, and a set of
flags 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 flags value is formed by OR'ing the following values:
MPOOL_PAGE_REQUEST- Allocate a new page with a specific page number.
MPOOL_PAGE_NEXT- Allocate a new page with the next page number.
The function
mpool_delete()
deletes the specified page from a pool and frees the page. It takes an
MPOOL pointer and a page as arguments. The page must
have been generated by mpool_new().
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 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 flags value is formed by OR'ing 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
routines fstat(2) and
malloc(3), or the following:
- [
ESPIPE] - The given file descriptor is a pipe.
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 pread(2),
pwrite(2), and
malloc(3).
The mpool_sync() function may fail and set
errno for any of the errors specified for the library
routine pwrite(2).
The mpool_close() function may fail and
set errno for any of the errors specified for the
library routine free(3).
The mpool_delete() always acts as if it
succeeded.