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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)mpool.3 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD: head/lib/libc/db/man/mpool.3 223214 2011-06-18 00:10:21Z delphij $ 30.\" 31.Dd June 17, 2011 32.Dt MPOOL 3 33.Os 34.Sh NAME 35.Nm mpool 36.Nd "shared memory buffer pool" 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In db.h 41.In mpool.h 42.Ft MPOOL * 43.Fn mpool_open "void *key" "int fd" "pgno_t pagesize" "pgno_t maxcache" 44.Ft void 45.Fo mpool_filter 46.Fa "MPOOL *mp" 47.Fa "void (*pgin)(void *, pgno_t, void *)" 48.Fa "void (*pgout)(void *, pgno_t, void *)" 49.Fa "void *pgcookie" 50.Fc 51.Ft void * 52.Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr" "unsigned int flags" 53.Ft int 54.Fn mpool_delete "MPOOL *mp" "void *page" 55.Ft void * 56.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "unsigned int flags" 57.Ft int 58.Fn mpool_put "MPOOL *mp" "void *pgaddr" "unsigned int flags" 59.Ft int 60.Fn mpool_sync "MPOOL *mp" 61.Ft int 62.Fn mpool_close "MPOOL *mp" 63.Sh DESCRIPTION 64The 65.Nm 66library interface is intended to provide page oriented buffer management 67of files. 68.Pp 69The 70.Fn mpool_open 71function initializes a memory pool. 72The 73.Fa key 74argument is currently ignored. 75The 76.Fa fd 77argument is a file descriptor for the underlying file, which must be seekable. 78.Pp 79The 80.Fa pagesize 81argument is the size, in bytes, of the pages into which the file is broken up. 82The 83.Fa maxcache 84argument is the maximum number of pages from the underlying file to cache 85at any one time. 86This value is not relative to the number of processes which share a file's 87buffers, but will be the largest value specified by any of the processes 88sharing the file. 89.Pp 90The 91.Fn mpool_filter 92function is intended to make transparent input and output processing of the 93pages possible. 94If the 95.Fa pgin 96function is specified, it is called each time a buffer is read into the memory 97pool from the backing file. 98If the 99.Fa pgout 100function is specified, it is called each time a buffer is written into the 101backing file. 102Both functions are called with the 103.Fa pgcookie 104pointer, the page number and a pointer to the page to being read or written. 105.Pp 106The function 107.Fn mpool_new 108takes an 109.Dv MPOOL 110pointer, an address, and a set of flags as arguments. 111If a new page can be allocated, a pointer to the page is returned and 112the page number is stored into the 113.Fa pgnoaddr 114address. 115Otherwise, 116.Dv NULL 117is returned and 118.Va errno 119is set. 120The flags value is formed by 121.Tn OR Ns 'ing 122the following values: 123.Bl -tag -width Ds 124.It Dv MPOOL_PAGE_REQUEST 125Allocate a new page with a specific page number. 126.It Dv MPOOL_PAGE_NEXT 127Allocate a new page with the next page number. 128.El 129.Pp 130The function 131.Fn mpool_delete 132deletes the specified page from a pool and frees the page. 133It takes an 134.Dv MPOOL 135pointer and a page as arguments. 136The page must have been generated by 137.Fn mpool_new . 138.Pp 139The 140.Fn mpool_get 141function takes a 142.Ft MPOOL 143pointer and a page number as arguments. 144If the page exists, a pointer to the page is returned. 145Otherwise, 146.Dv NULL 147is returned and 148.Va errno 149is set. 150The 151.Fa flags 152argument is specified by 153.Em or Ns 'ing 154any of the following values: 155.Bl -tag -width indent 156.It Dv MPOOL_IGNOREPIN 157The page returned is not pinned; 158page will otherwise be pinned on return. 159.El 160.Pp 161The 162.Fn mpool_put 163function unpins the page referenced by 164.Fa pgaddr . 165The 166.Fa pgaddr 167argument 168must be an address previously returned by 169.Fn mpool_get 170or 171.Fn mpool_new . 172The 173.Fa flags 174argument is specified by 175.Em or Ns 'ing 176any of the following values: 177.Bl -tag -width indent 178.It Dv MPOOL_DIRTY 179The page has been modified and needs to be written to the backing file. 180.El 181.Pp 182The 183.Fn mpool_put 184function 185returns 0 on success and -1 if an error occurs. 186.Pp 187The 188.Fn mpool_sync 189function writes all modified pages associated with the 190.Ft MPOOL 191pointer to the 192backing file. 193The 194.Fn mpool_sync 195function 196returns 0 on success and -1 if an error occurs. 197.Pp 198The 199.Fn mpool_close 200function free's up any allocated memory associated with the memory pool 201cookie. 202Modified pages are 203.Em not 204written to the backing file. 205The 206.Fn mpool_close 207function 208returns 0 on success and -1 if an error occurs. 209.Sh ERRORS 210The 211.Fn mpool_open 212function may fail and set 213.Va errno 214for any of the errors specified for the library routine 215.Xr malloc 3 . 216.Pp 217The 218.Fn mpool_get 219function may fail and set 220.Va errno 221for the following: 222.Bl -tag -width Er 223.It Bq Er EINVAL 224The requested record does not exist. 225.El 226.Pp 227The 228.Fn mpool_new 229and 230.Fn mpool_get 231functions may fail and set 232.Va errno 233for any of the errors specified for the library routines 234.Xr read 2 , 235.Xr write 2 , 236and 237.Xr malloc 3 . 238.Pp 239The 240.Fn mpool_sync 241function may fail and set 242.Va errno 243for any of the errors specified for the library routine 244.Xr write 2 . 245.Pp 246The 247.Fn mpool_close 248function may fail and set 249.Va errno 250for any of the errors specified for the library routine 251.Xr free 3 . 252.Sh SEE ALSO 253.Xr btree 3 , 254.Xr dbopen 3 , 255.Xr hash 3 , 256.Xr recno 3 257