man3/mpool.3

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  32 .\"     @(#)mpool.3     8.1 (Berkeley) 6/4/93
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  34 .TH MPOOL 3 1993-06-04 "" "Linux Programmer's Manual"
  35 .UC 7
  36 .SH NAME
  37 mpool \- shared memory buffer pool
  38 .SH SYNOPSIS
  39 .nf
  40 .B #include <db.h>
  41 .B #include <mpool.h>
  42 .sp
  43 .BI "MPOOL *mpool_open(DBT *" key ", int " fd ", pgno_t " pagesize \
  44 ", pgno_t " maxcache );
  45 .sp
  46 .BI "void mpool_filter(MPOOL *" mp ", void (*pgin)(void *, pgno_t, void *),"
  47 .BI "                  void (*" pgout ")(void *, pgno_t, void *),"
  48 .BI "                  void *" pgcookie );
  49 .sp
  50 .BI "void *mpool_new(MPOOL *" mp ", pgno_t *" pgnoaddr );
  51 .sp
  52 .BI "void *mpool_get(MPOOL *" mp ", pgno_t " pgno ", unsigned int " flags );
  53 .sp
  54 .BI "int mpool_put(MPOOL *" mp ", void *" pgaddr ", unsigned int " flags );
  55 .sp
  56 .BI "int mpool_sync(MPOOL *" mp );
  57 .sp
  58 .BI "int mpool_close(MPOOL *" mp );
  59 .fi
  60 .SH DESCRIPTION
  61 .I Mpool
  62 is the library interface intended to provide page oriented buffer management
  63 of files.
  64 The buffers may be shared between processes.
  65 .PP
  66 The function
  67 .BR mpool_open ()
  68 initializes a memory pool.
  69 The
  70 .I key
  71 argument is the byte string used to negotiate between multiple
  72 processes wishing to share buffers.
  73 If the file buffers are mapped in shared memory, all processes using
  74 the same key will share the buffers.
  75 If
  76 .I key
  77 is NULL, the buffers are mapped into private memory.
  78 The
  79 .I fd
  80 argument is a file descriptor for the underlying file, which must be seekable.
  81 If
  82 .I key
  83 is non-NULL and matches a file already being mapped, the
  84 .I fd
  85 argument is ignored.
  86 .PP
  87 The
  88 .I pagesize
  89 argument is the size, in bytes, of the pages into which the file is broken up.
  90 The
  91 .I maxcache
  92 argument is the maximum number of pages from the underlying file to cache
  93 at any one time.
  94 This value is not relative to the number of processes which share a file's
  95 buffers, but will be the largest value specified by any of the processes
  96 sharing the file.
  97 .PP
  98 The
  99 .BR mpool_filter ()
 100 function is intended to make transparent input and output processing of the
 101 pages possible.
 102 If the
 103 .I pgin
 104 function is specified, it is called each time a buffer is read into the memory
 105 pool from the backing file.
 106 If the
 107 .I pgout
 108 function is specified, it is called each time a buffer is written into the
 109 backing file.
 110 Both functions are called with the
 111 .I pgcookie
 112 pointer, the page number and a pointer to the page to being read or written.
 113 .PP
 114 The function
 115 .BR mpool_new ()
 116 takes an
 117 .I MPOOL
 118 pointer and an address as arguments.
 119 If a new page can be allocated, a pointer to the page is returned and
 120 the page number is stored into the
 121 .I pgnoaddr
 122 address.
 123 Otherwise, NULL is returned and
 124 .I errno
 125 is set.
 126 .PP
 127 The function
 128 .BR mpool_get ()
 129 takes an
 130 .I MPOOL
 131 pointer and a page number as arguments.
 132 If the page exists, a pointer to the page is returned.
 133 Otherwise, NULL is returned and
 134 .I errno
 135 is set.
 136 The
 137 .I flags
 138 argument is not currently used.
 139 .PP
 140 The function
 141 .BR mpool_put ()
 142 unpins the page referenced by
 143 .IR pgaddr .
 144 .I pgaddr
 145 must be an address previously returned by
 146 .BR mpool_get ()
 147 or
 148 .BR mpool_new ().
 149 The flag value is specified by
 150 .IR or 'ing
 151 any of the following values:
 152 .TP
 153 .B MPOOL_DIRTY
 154 The page has been modified and needs to be written to the backing file.
 155 .PP
 156 .BR mpool_put ()
 157 returns 0 on success and \-1 if an error occurs.
 158 .PP
 159 The function
 160 .BR mpool_sync ()
 161 writes all modified pages associated with the
 162 .I MPOOL
 163 pointer to the
 164 backing file.
 165 .BR mpool_sync ()
 166 returns 0 on success and \-1 if an error occurs.
 167 .PP
 168 The
 169 .BR mpool_close ()
 170 function free's up any allocated memory associated with the memory pool
 171 cookie.
 172 Modified pages are
 173 .B not
 174 written to the backing file.
 175 .BR mpool_close ()
 176 returns 0 on success and \-1 if an error occurs.
 177 .SH ERRORS
 178 The
 179 .BR mpool_open ()
 180 function may fail and set
 181 .I errno
 182 for any of the errors specified for the library routine
 183 .BR malloc (3).
 184 .PP
 185 The
 186 .BR mpool_get ()
 187 function may fail and set
 188 .I errno
 189 for the following:
 190 .TP 15
 191 .B EINVAL
 192 The requested record doesn't exist.
 193 .PP
 194 The
 195 .BR mpool_new ()
 196 and
 197 .BR mpool_get ()
 198 functions may fail and set
 199 .I errno
 200 for any of the errors specified for the library routines
 201 .BR read (2),
 202 .BR write (2),
 203 and
 204 .BR malloc (3).
 205 .PP
 206 The
 207 .BR mpool_sync ()
 208 function may fail and set
 209 .I errno
 210 for any of the errors specified for the library routine
 211 .BR write (2).
 212 .PP
 213 The
 214 .BR mpool_close ()
 215 function may fail and set
 216 .I errno
 217 for any of the errors specified for the library routine
 218 .BR free (3).
 219 .SH "CONFORMING TO"
 220 Not in POSIX.1-2001.
 221 Present on the BSDs.
 222 .SH "SEE ALSO"
 223 .BR btree (3),
 224 .BR dbopen (3),
 225 .BR hash (3),
 226 .BR recno (3)