mpool(3) - Linux manual page (original) (raw)
mpool(3) Library Functions Manual mpool(3)
NAME top
mpool - shared memory buffer poolLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <db.h>**
**#include <mpool.h>**
**MPOOL *mpool_open(DBT ***_key_**, int** _fd_**, pgno_t** _pagesize_**, pgno_t** _maxcache_**);**
**void mpool_filter(MPOOL ***_mp_**,**
**typeof(void (void *, pgno_t, void *)) ***_pgin_**,**
**typeof(void (void *, pgno_t, void *)) ***_pgout_**,**
**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_**);**DESCRIPTION top
_Note well_: This page documents interfaces provided up until glibc
2.1. Since glibc 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](../man3/errno.3.html)_ 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](../man3/errno.3.html)_ 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.ERRORS top
The **mpool_open**() function may fail and set _[errno](../man3/errno.3.html)_ for any of the
errors specified for the library routine [malloc(3)](../man3/malloc.3.html).
The **mpool_get**() function may fail and set _[errno](../man3/errno.3.html)_ for the following:
**EINVAL** The requested record doesn't exist.
The **mpool_new**() and **mpool_get**() functions may fail and set _[errno](../man3/errno.3.html)_
for any of the errors specified for the library routines [read(2)](../man2/read.2.html),
[write(2)](../man2/write.2.html), and [malloc(3)](../man3/malloc.3.html).
The **mpool_sync**() function may fail and set _[errno](../man3/errno.3.html)_ for any of the
errors specified for the library routine [write(2)](../man2/write.2.html).
The **mpool_close**() function may fail and set _[errno](../man3/errno.3.html)_ for any of the
errors specified for the library routine [free(3)](../man3/free.3.html).STANDARDS top
BSD.SEE ALSO top
[btree(3)](../man3/btree.3.html), [dbopen(3)](../man3/dbopen.3.html), [hash(3)](../man3/hash.3.html), [recno(3)](../man3/recno.3.html)COLOPHON top
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man-pages@man7.org4.4 Berkeley Distribution 2024-12-13 mpool(3)
Pages that refer to this page:btree(3), dbopen(3), hash(3), recno(3)