1RRDTHREADS(1) rrdtool RRDTHREADS(1)
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6 rrdthreads - Provisions for linking the RRD library to use in
7 multi-threaded programs
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10 Using librrd in multi-threaded programs requires some extra precau‐
11 tions, as the RRD library in its original form was not thread-safe at
12 all. This document describes requirements and pitfalls on the way to
13 use the multi-threaded version of librrd in your own programs. It also
14 gives hints for future RRD development to keep the library thread-safe.
15 Currently only some RRD operations are implemented in a thread-safe
17 way. They all end in the usual ""_r"" suffix.
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20 In order to use librrd in multi-threaded programs you must:
21 · Link with librrd_th instead of librrd (use "-lrrd_th" when linking)
23 · Use the ""_r"" functions instead of the normal API-functions
25 · Do not use any at-style time specifications. Parsing of such time
27 specifications is terribly non-thread-safe.
28 · Never use non *"_r" functions unless it is explicitly documented
30 that the function is tread-safe.
31 · Every thread SHOULD call "rrd_get_context()" before its first call
33 to any "librrd_th" function in order to set up thread specific
34 data. This is not strictly required, but it is the only way to test
35 if memory allocation can be done by this function. Otherwise the
36 program may die with a SIGSEGV in a low-memory situation.
37 · Always call "rrd_error_clear()" before any call to the library.
39 Otherwise the call might fail due to some earlier error.
40 NOTES FOR RRD CONTRIBUTORS
42 Some precautions must be followed when developing RRD from now on:
44 · Only use thread-safe functions in library code. Many often used
46 libc functions aren't thread-safe. Take care in the following situ‐
47 ations or when using the following library functions:
48 · Direct calls to "strerror()" must be avoided: use "rrd_str‐
50 error()" instead, it provides a per-thread error message.
51 · The "getpw*", "getgr*", "gethost*" function families (and some
53 more "get*" functions) are not thread-safe: use the *"_r" vari‐
54 ants
55 · Time functions: "asctime", "ctime", "gmtime", "localtime": use
57 *"_r" variants
58 · "strtok": use "strtok_r"
60 · "tmpnam": use "tmpnam_r"
62 · Many others (lookup documentation)
64 · A header file named rrd_is_thread_safe.h is provided that works
66 with the GNU C-preprocessor to "poison" some of the most common
67 non-thread-safe functions using the "#pragma GCC poison" directive.
68 Just include this header in source files you want to keep
69 thread-safe.
70 · Do not introduce global variables!
72 If you really, really have to use a global variable you may add a
74 new field to the "rrd_context" structure and modify rrd_error.c,
75 rrd_thread_safe.c and rrd_non_thread_safe.c
76 · Do not use "getopt" or "getopt_long" in *"_r" (neither directly nor
78 indirectly).
79 "getopt" uses global variables and behaves badly in a multi-
81 threaded application when called concurrently. Instead provide a
82 *_r function taking all options as function parameters. You may
83 provide argc and **argv arguments for variable length argument
84 lists. See "rrd_update_r" as an example.
85 · Do not use the "parsetime" function!
87 It uses lots of global variables. You may use it in functions not
89 designed to be thread-safe, like in functions wrapping the "_r"
90 version of some operation (e.g., "rrd_create", but not in "rrd_cre‐
91 ate_r")
92 CURRENTLY IMPLEMENTED THREAD SAFE FUNCTIONS
94 Currently there exist thread-safe variants of "rrd_update", "rrd_cre‐
96 ate", "rrd_dump", "rrd_info", "rrd_last", and "rrd_fetch".
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99 Peter Stamfest <peter@stamfest.at>
1001.2.27 2008-02-17 RRDTHREADS(1)