db/man/mpool.3

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  32 .\"     @(#)mpool.3     8.1 (Berkeley) 6/4/93
  33 .\" $FreeBSD: src/lib/libc/db/man/mpool.3,v 1.9 2001/10/01 16:08:50 ru Exp $
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  35 .Dd June 4, 1993
  36 .Dt MPOOL 3
  37 .Os
  38 .Sh NAME
  39 .Nm mpool
  40 .Nd "shared memory buffer pool"
  41 .Sh SYNOPSIS
  42 .In db.h
  43 .In mpool.h
  44 .Ft MPOOL *
  45 .Fn mpool_open "void *key" "int fd" "pgno_t pagesize" "pgno_t maxcache"
  46 .Ft void
  47 .Fo mpool_filter
  48 .Fa "MPOOL *mp"
  49 .Fa "void (*pgin)(void *, pgno_t, void *)"
  50 .Fa "void (*pgout)(void *, pgno_t, void *)"
  51 .Fa "void *pgcookie"
  52 .Fc
  53 .Ft void *
  54 .Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr"
  55 .Ft void *
  56 .Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags"
  57 .Ft int
  58 .Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags"
  59 .Ft int
  60 .Fn mpool_sync "MPOOL *mp"
  61 .Ft int
  62 .Fn mpool_close "MPOOL *mp"
  63 .Sh DESCRIPTION
  64 .Nm Mpool
  65 is the library interface intended to provide page oriented buffer management
  66 of files.
  67 The buffers may be shared between processes.
  68 .Pp
  69 The function
  70 .Fn mpool_open
  71 initializes a memory pool.
  72 The
  73 .Fa key
  74 argument is the byte string used to negotiate between multiple
  75 processes wishing to share buffers.
  76 If the file buffers are mapped in shared memory, all processes using
  77 the same key will share the buffers.
  78 If
  79 .Fa key
  80 is
  81 .Dv NULL ,
  82 the buffers are mapped into private memory.
  83 The
  84 .Fa fd
  85 argument is a file descriptor for the underlying file, which must be seekable.
  86 If
  87 .Fa key
  88 is
  89 .No non\- Ns Dv NULL
  90 and matches a file already being mapped, the
  91 .Fa fd
  92 argument is ignored.
  93 .Pp
  94 The
  95 .Fa pagesize
  96 argument is the size, in bytes, of the pages into which the file is broken up.
  97 The
  98 .Fa maxcache
  99 argument is the maximum number of pages from the underlying file to cache
 100 at any one time.
 101 This value is not relative to the number of processes which share a file's
 102 buffers, but will be the largest value specified by any of the processes
 103 sharing the file.
 104 .Pp
 105 The
 106 .Fn mpool_filter
 107 function is intended to make transparent input and output processing of the
 108 pages possible.
 109 If the
 110 .Fa pgin
 111 function is specified, it is called each time a buffer is read into the memory
 112 pool from the backing file.
 113 If the
 114 .Fa pgout
 115 function is specified, it is called each time a buffer is written into the
 116 backing file.
 117 Both functions are called with the
 118 .Fa pgcookie
 119 pointer, the page number and a pointer to the page to being read or written.
 120 .Pp
 121 The function
 122 .Fn mpool_new
 123 takes an
 124 .Ft MPOOL
 125 pointer and an address as arguments.
 126 If a new page can be allocated, a pointer to the page is returned and
 127 the page number is stored into the
 128 .Fa pgnoaddr
 129 address.
 130 Otherwise,
 131 .Dv NULL
 132 is returned and
 133 .Va errno
 134 is set.
 135 .Pp
 136 The function
 137 .Fn mpool_get
 138 takes a
 139 .Ft MPOOL
 140 pointer and a page number as arguments.
 141 If the page exists, a pointer to the page is returned.
 142 Otherwise,
 143 .Dv NULL
 144 is returned and
 145 .Va errno
 146 is set.
 147 The
 148 .Fa flags
 149 parameter is not currently used.
 150 .Pp
 151 The function
 152 .Fn mpool_put
 153 unpins the page referenced by
 154 .Fa pgaddr .
 155 .Fa Pgaddr
 156 must be an address previously returned by
 157 .Fn mpool_get
 158 or
 159 .Fn mpool_new .
 160 The
 161 .Fa flags
 162 value is specified by
 163 .Em or Ns 'ing
 164 any of the following values:
 165 .Bl -tag -width indent
 166 .It Dv MPOOL_DIRTY
 167 The page has been modified and needs to be written to the backing file.
 168 .El
 169 .Pp
 170 .Fn Mpool_put
 171 returns 0 on success and -1 if an error occurs.
 172 .Pp
 173 The function
 174 .Fn mpool_sync
 175 writes all modified pages associated with the
 176 .Ft MPOOL
 177 pointer to the
 178 backing file.
 179 .Fn Mpool_sync
 180 returns 0 on success and -1 if an error occurs.
 181 .Pp
 182 The
 183 .Fn mpool_close
 184 function free's up any allocated memory associated with the memory pool
 185 cookie.
 186 Modified pages are
 187 .Em not
 188 written to the backing file.
 189 .Fn Mpool_close
 190 returns 0 on success and -1 if an error occurs.
 191 .Sh ERRORS
 192 The
 193 .Fn mpool_open
 194 function may fail and set
 195 .Va errno
 196 for any of the errors specified for the library routine
 197 .Xr malloc 3 .
 198 .Pp
 199 The
 200 .Fn mpool_get
 201 function may fail and set
 202 .Va errno
 203 for the following:
 204 .Bl -tag -width Er
 205 .It Bq Er EINVAL
 206 The requested record doesn't exist.
 207 .El
 208 .Pp
 209 The
 210 .Fn mpool_new
 211 and
 212 .Fn mpool_get
 213 functions may fail and set
 214 .Va errno
 215 for any of the errors specified for the library routines
 216 .Xr read 2 ,
 217 .Xr write 2 ,
 218 and
 219 .Xr malloc 3 .
 220 .Pp
 221 The
 222 .Fn mpool_sync
 223 function may fail and set
 224 .Va errno
 225 for any of the errors specified for the library routine
 226 .Xr write 2 .
 227 .Pp
 228 The
 229 .Fn mpool_close
 230 function may fail and set
 231 .Va errno
 232 for any of the errors specified for the library routine
 233 .Xr free 3 .
 234 .Sh SEE ALSO
 235 .Xr btree 3 ,
 236 .Xr dbopen 3 ,
 237 .Xr hash 3 ,
 238 .Xr recno 3