пул буферов разделяемой памяти (shared memory buffer pool)
Имя (Name)
mpool - shared memory buffer pool
Синопсис (Synopsis)
#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, unsigned int flags);
int mpool_put(MPOOL *mp, void *pgaddr, unsigned int flags);
int mpool_sync(MPOOL *mp);
int mpool_close(MPOOL *mp);
Описание (Description)
Note well: This page documents interfaces provided in glibc up
until version 2.1. Since version 2.2, glibc no longer provides
these interfaces. Probably, you are looking for the APIs
provided by the libdb library instead.
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 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 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 argument 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 ORing 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.
Ошибки (Error)
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).
Стандарты (Conforming to)
Not in POSIX.1. Present on the BSDs.
Смотри также (See also)
btree(3), dbopen(3), hash(3), recno(3)
