MPOOL(3) BSD Programmer's Manual MPOOL(3)
mpool_open, mpool_filter, mpool_new, mpool_delete, mpool_get, mpool_put,
mpool_sync, mpool_close - shared memory buffer pool
#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);
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 ig-
nored.
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 re-
lative 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 speci-
fied, 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 be-
ing 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. Oth-
erwise, 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 ar-
guments. If the page exists, a pointer to the page is returned. Other-
wise, 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.
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 follow-
ing:
[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.
btree(3), dbopen(3), hash(3), recno(3)
MirBSD #10-current February 25, 1999 1