mirror of https://github.com/mkerrisk/man-pages
235 lines
6.5 KiB
Groff
235 lines
6.5 KiB
Groff
.\" Copyright (c) 1990, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\" %%%LICENSE_END
|
|
.\"
|
|
.\" @(#)mpool.3 8.1 (Berkeley) 6/4/93
|
|
.\"
|
|
.TH MPOOL 3 2017-09-15 "" "Linux Programmer's Manual"
|
|
.UC 7
|
|
.SH NAME
|
|
mpool \- shared memory buffer pool
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.B #include <db.h>
|
|
.B #include <mpool.h>
|
|
.PP
|
|
.BI "MPOOL *mpool_open(DBT *" key ", int " fd ", pgno_t " pagesize \
|
|
", pgno_t " maxcache );
|
|
.PP
|
|
.BI "void mpool_filter(MPOOL *" mp ", void (*pgin)(void *, pgno_t, void *),"
|
|
.BI " void (*" pgout ")(void *, pgno_t, void *),"
|
|
.BI " void *" pgcookie );
|
|
.PP
|
|
.BI "void *mpool_new(MPOOL *" mp ", pgno_t *" pgnoaddr );
|
|
.PP
|
|
.BI "void *mpool_get(MPOOL *" mp ", pgno_t " pgno ", unsigned int " flags );
|
|
.PP
|
|
.BI "int mpool_put(MPOOL *" mp ", void *" pgaddr ", unsigned int " flags );
|
|
.PP
|
|
.BI "int mpool_sync(MPOOL *" mp );
|
|
.PP
|
|
.BI "int mpool_close(MPOOL *" mp );
|
|
.fi
|
|
.SH DESCRIPTION
|
|
.IR "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
|
|
.I libdb
|
|
library instead.
|
|
.PP
|
|
.I Mpool
|
|
is the library interface intended to provide page oriented buffer management
|
|
of files.
|
|
The buffers may be shared between processes.
|
|
.PP
|
|
The function
|
|
.BR mpool_open ()
|
|
initializes a memory pool.
|
|
The
|
|
.I 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
|
|
.I key
|
|
is NULL, the buffers are mapped into private memory.
|
|
The
|
|
.I fd
|
|
argument is a file descriptor for the underlying file, which must be seekable.
|
|
If
|
|
.I key
|
|
is non-NULL and matches a file already being mapped, the
|
|
.I fd
|
|
argument is ignored.
|
|
.PP
|
|
The
|
|
.I pagesize
|
|
argument is the size, in bytes, of the pages into which the file is broken up.
|
|
The
|
|
.I 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.
|
|
.PP
|
|
The
|
|
.BR mpool_filter ()
|
|
function is intended to make transparent input and output processing of the
|
|
pages possible.
|
|
If the
|
|
.I pgin
|
|
function is specified, it is called each time a buffer is read into the memory
|
|
pool from the backing file.
|
|
If the
|
|
.I pgout
|
|
function is specified, it is called each time a buffer is written into the
|
|
backing file.
|
|
Both functions are called with the
|
|
.I pgcookie
|
|
pointer, the page number and a pointer to the page to being read or written.
|
|
.PP
|
|
The function
|
|
.BR mpool_new ()
|
|
takes an
|
|
.I 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
|
|
.I pgnoaddr
|
|
address.
|
|
Otherwise, NULL is returned and
|
|
.I errno
|
|
is set.
|
|
.PP
|
|
The function
|
|
.BR mpool_get ()
|
|
takes an
|
|
.I MPOOL
|
|
pointer and a page number as arguments.
|
|
If the page exists, a pointer to the page is returned.
|
|
Otherwise, NULL is returned and
|
|
.I errno
|
|
is set.
|
|
The
|
|
.I flags
|
|
argument is not currently used.
|
|
.PP
|
|
The function
|
|
.BR mpool_put ()
|
|
unpins the page referenced by
|
|
.IR pgaddr .
|
|
.I pgaddr
|
|
must be an address previously returned by
|
|
.BR mpool_get ()
|
|
or
|
|
.BR mpool_new ().
|
|
The flag value is specified by ORing
|
|
any of the following values:
|
|
.TP
|
|
.B MPOOL_DIRTY
|
|
The page has been modified and needs to be written to the backing file.
|
|
.PP
|
|
.BR mpool_put ()
|
|
returns 0 on success and \-1 if an error occurs.
|
|
.PP
|
|
The function
|
|
.BR mpool_sync ()
|
|
writes all modified pages associated with the
|
|
.I MPOOL
|
|
pointer to the
|
|
backing file.
|
|
.BR mpool_sync ()
|
|
returns 0 on success and \-1 if an error occurs.
|
|
.PP
|
|
The
|
|
.BR mpool_close ()
|
|
function free's up any allocated memory associated with the memory pool
|
|
cookie.
|
|
Modified pages are
|
|
.B not
|
|
written to the backing file.
|
|
.BR mpool_close ()
|
|
returns 0 on success and \-1 if an error occurs.
|
|
.SH ERRORS
|
|
The
|
|
.BR mpool_open ()
|
|
function may fail and set
|
|
.I errno
|
|
for any of the errors specified for the library routine
|
|
.BR malloc (3).
|
|
.PP
|
|
The
|
|
.BR mpool_get ()
|
|
function may fail and set
|
|
.I errno
|
|
for the following:
|
|
.TP 15
|
|
.B EINVAL
|
|
The requested record doesn't exist.
|
|
.PP
|
|
The
|
|
.BR mpool_new ()
|
|
and
|
|
.BR mpool_get ()
|
|
functions may fail and set
|
|
.I errno
|
|
for any of the errors specified for the library routines
|
|
.BR read (2),
|
|
.BR write (2),
|
|
and
|
|
.BR malloc (3).
|
|
.PP
|
|
The
|
|
.BR mpool_sync ()
|
|
function may fail and set
|
|
.I errno
|
|
for any of the errors specified for the library routine
|
|
.BR write (2).
|
|
.PP
|
|
The
|
|
.BR mpool_close ()
|
|
function may fail and set
|
|
.I errno
|
|
for any of the errors specified for the library routine
|
|
.BR free (3).
|
|
.SH CONFORMING TO
|
|
Not in POSIX.1.
|
|
Present on the BSDs.
|
|
.SH SEE ALSO
|
|
.BR btree (3),
|
|
.BR dbopen (3),
|
|
.BR hash (3),
|
|
.BR recno (3)
|