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
)
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 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
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.
The mpool_get function may fail and set errno for the following:
EINVAL
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).