1 RRDTHREADS(1) rrdtool RRDTHREADS(1)
6 rrdthreads - Provisions for linking the RRD library to use
7 in multi-threaded programs
9 S
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10 Using librrd in multi-threaded programs requires some
11 extra precautions, as the RRD library in its original form
12 was not thread-safe at all. This document describes
13 requirements and pitfalls on the way to use the multi-
14 threaded version of librrd in your own programs. It also
15 gives hints for future RRD development to keep the library
18 Currently only some RRD operations are implemented in a
19 thread-safe way. They all end in the usual ""_r"" suffix.
21 D
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22 In order to use librrd in multi-threaded programs you
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\bo Link with _
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\bd (use "-lrrd_th"
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\bo Use the ""_r"" functions instead of the normal API-
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\bo Do not use any at-style time specifications. Parsing
32 of such time specifications is terribly
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\bo Never use non *"_r" functions unless it is explicitly
36 documented that the function is tread-safe.
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\bo Every thread SHOULD call "rrd_get_context()" before
39 its first call to any "librrd_th" function in order to
40 set up thread specific data. This is not strictly
41 required, but it is the only way to test if memory
42 allocation can be done by this function. Otherwise the
43 program may die with a SIGSEGV in a low-memory situa-
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\bo Always call "rrd_error_clear()" before any call to the
47 library. Otherwise the call might fail due to some
50 N
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52 Some precautions must be followed when developing RRD from
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\bo Only use thread-safe functions in library code. Many
56 often used libc functions aren't thread-safe. Take
57 care in the following situations or when using the
58 following library functions:
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\bo Direct calls to "strerror()" must be avoided: use
61 "rrd_strerror()" instead, it provides a per-thread
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\bo The "getpw*", "getgr*", "gethost*" function fami-
65 lies (and some more "get*" functions) are not
66 thread-safe: use the *"_r" variants
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\bo Time functions: "asctime", "ctime", "gmtime",
69 "localtime": use *"_r" variants
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\bo "strtok": use "strtok_r"
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\bo "tmpnam": use "tmpnam_r"
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\bo Many others (lookup documentation)
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\bo A header file named _
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78 that works with the GNU C-preprocessor to "poison"
79 some of the most common non-thread-safe functions
80 using the "#pragma GCC poison" directive. Just include
81 this header in source files you want to keep
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\bo Do not introduce global variables!
86 If you really, really have to use a global variable
87 you may add a new field to the "rrd_context" structure
88 and modify _
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89 _
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\bo Do not use "getopt" or "getopt_long" in *"_r" (neither
92 directly nor indirectly).
94 "getopt" uses global variables and behaves badly in a
95 multi-threaded application when called concurrently.
96 Instead provide a *_r function taking all options as
97 function parameters. You may provide argc and **argv
98 arguments for variable length argument lists. See
99 "rrd_update_r" as an example.
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\bo Do not use the "parsetime" function!
103 It uses lots of global variables. You may use it in
104 functions not designed to be thread-safe, like in
105 functions wrapping the "_r" version of some operation
106 (e.g., "rrd_create", but not in "rrd_create_r")
108 C
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110 Currently there exist thread-safe variants of
111 "rrd_update", "rrd_create", "rrd_dump", "rrd_info" and
114 A
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115 Peter Stamfest <peter@stamfest.at>
119 1.2.10 2005-06-17 RRDTHREADS(1)