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1 perry 1 MPOOL
2 !!!MPOOL
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 ERRORS
7 SEE ALSO
8 ----
9 !!NAME
10
11
12 mpool - shared memory buffer pool
13 !!SYNOPSIS
14
15
16 __#include
17 __
18 !!DESCRIPTION
19
20
21 ''Mpool'' is the library interface intended to provide
22 page oriented buffer management of files. The buffers may be
23 shared between processes.
24
25
26 The function ''mpool_open'' initializes a memory pool.
27 The ''key'' argument is the byte string used to negotiate
28 between multiple processes wishing to share buffers. If the
29 file buffers are mapped in shared memory, all processes
30 using the same key will share the buffers. If ''key'' is
31 NULL, the buffers are mapped into private memory. The
32 ''fd'' argument is a file descriptor for the underlying
33 file, which must be seekable. If ''key'' is non-NULL and
34 matches a file already being mapped, the ''fd'' argument
35 is ignored.
36
37
38 The ''pagesize'' argument is the size, in bytes, of the
39 pages into which the file is broken up. The ''maxcache''
40 argument is the maximum number of pages from the underlying
41 file to cache at any one time. This value is not relative to
42 the number of processes which share a file's buffers, but
43 will be the largest value specified by any of the processes
44 sharing the file.
45
46
47 The ''mpool_filter'' function is intended to make
48 transparent input and output processing of the pages
49 possible. If the ''pgin'' function is specified, it is
50 called each time a buffer is read into the memory pool from
51 the backing file. If the ''pgout'' function is specified,
52 it is called each time a buffer is written into the backing
53 file. Both functions are are called with the ''pgcookie''
54 pointer, the page number and a pointer to the page to being
55 read or written.
56
57
58 The function ''mpool_new'' takes an MPOOL pointer and an
59 address as arguments. If a new page can be allocated, a
60 pointer to the page is returned and the page number is
61 stored into the ''pgnoaddr'' address. Otherwise, NULL is
62 returned and errno is set.
63
64
65 The function ''mpool_get'' takes a MPOOL pointer and a
66 page number as arguments. If the page exists, a pointer to
67 the page is returned. Otherwise, NULL is returned and errno
68 is set. The flags parameter is not currently
69 used.
70
71
72 The function ''mpool_put'' unpins the page referenced by
73 ''pgaddr''. ''Pgaddr'' must be an address previously
74 returned by ''mpool_get'' or ''mpool_new''. The flag
75 value is specified by ''or'''ing any of the following
76 values:
77
78
79 MPOOL_DIRTY
80
81
82 The page has been modified and needs to be written to the
83 backing file.
84
85
86 ''Mpool_put'' returns 0 on success and -1 if an error
87 occurs.
88
89
90 The function ''mpool_sync'' writes all modified pages
91 associated with the MPOOL pointer to the backing file.
92 ''Mpool_sync'' returns 0 on success and -1 if an error
93 occurs.
94
95
96 The ''mpool_close'' function free's up any allocated
97 memory associated with the memory pool cookie. Modified
98 pages are __not__ written to the backing file.
99 ''Mpool_close'' returns 0 on success and -1 if an error
100 occurs.
101 !!ERRORS
102
103
104 The ''mpool_open'' function may fail and set ''errno''
105 for any of the errors specified for the library routine
106 malloc(3).
107
108
109 The ''mpool_get'' function may fail and set ''errno''
110 for the following:
111
112
113 [[EINVAL]
114
115
116 The requested record doesn't exist.
117
118
119 The ''mpool_new'' and ''mpool_get'' functions may fail
120 and set ''errno'' for any of the errors specified for the
121 library routines read(2)'', write''(2)'','' and
122 malloc(3).
123
124
125 The ''mpool_sync'' function may fail and set ''errno''
126 for any of the errors specified for the library routine
127 write(2).
128
129
130 The ''mpool_close'' function may fail and set
131 ''errno'' for any of the errors specified for the library
132 routine free(3).
133 !!SEE ALSO
134
135
136 dbopen(3), btree(3), hash(3),
137 recno(3)
138 ----
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