mpool, 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 );
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: 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.
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: 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).
dbopen(3), btree(3), hash(3), recno(3)
mpool(3)
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