mpool, mpool_open, mpool_filter, mpool_new, mpool_get,
mpool_put, mpool_sync, mpool_close, - shared memory buffer
pool
#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);
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 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 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.
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).
dbopen(3), btree(3), hash(3), recno(3)
June 4, 1993 MPOOL(3)
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