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RRDTHREADS(1) rrdtool RRDTHREADS(1) NAME rrdthreads - Provisions for linking the RRD library to use in multi-threaded programs SYNOPSIS Using librrd in multi-threaded programs requires some extra precautions. This document describes requirements and pitfalls on the way to use librrd in your own programs. It also gives hints for future RRD development to keep the library thread-safe. Since RRDtool 1.6, librrd is thread-safe and no separate thread-specific library is needed. DESCRIPTION In order to use librrd in multi-threaded programs you must: * Link with librrd (use "-lrrd" when linking) * Use the ""_r"" functions instead of the normal API-functions * Do not use any at-style time specifications. Parsing of such time spec- ifications is terribly non-thread-safe. * Never use non *"_r" functions unless it is explicitly documented that the function is thread-safe. * Every thread SHOULD call rrd_get_context() before its first call to any "librrd" function in order to set up thread specific data. This is not strictly required, but it is the only way to test if memory allocation can be done by this function. Otherwise the program may die with a SIGSEGV in a low-memory situation. * Always call rrd_clear_error() before any call to the library. Otherwise the call might fail due to some earlier error. NOTES FOR RRD CONTRIBUTORS Some precautions must be followed when developing RRD from now on: * Only use thread-safe functions in library code. Many often used libc functions aren't thread-safe. Take care in the following situations or when using the following library functions: * Direct calls to strerror() must be avoided: use rrd_strerror() in- stead, it provides a per-thread error message. * The "getpw*", "getgr*", "gethost*" function families (and some more "get*" functions) are not thread-safe: use the *"_r" variants * Time functions: "asctime", "ctime", "gmtime", "localtime": use *"_r" variants * "strtok": use "strtok_r" * "tmpnam": use "tmpnam_r" * Many others (lookup documentation) * A header file named rrd_is_thread_safe.h is provided that works with the GNU C-preprocessor to "poison" some of the most common non-thread- safe functions using the "#pragma GCC poison" directive. Just include this header in source files you want to keep thread-safe. * Do not introduce global variables! If you really, really have to use a global variable you may add a new field to the "rrd_context" structure and modify rrd_error.c, rrd_thread_safe.c and rrd_non_thread_safe.c * Do not use "getopt" or "getopt_long" in *"_r" (neither directly nor in- directly). "getopt" uses global variables and behaves badly in a multi-threaded application when called concurrently. Instead provide a *_r function taking all options as function parameters. You may provide argc and **argv arguments for variable length argument lists. See "rrd_update_r" as an example. * Do not use the "rrd_parsetime" function! It uses lots of global variables. You may use it in functions not de- signed to be thread-safe, like in functions wrapping the "_r" version of some operation (e.g., "rrd_create", but not in "rrd_create_r") CURRENTLY IMPLEMENTED THREAD SAFE FUNCTIONS Currently there exist thread-safe variants of "rrd_update", "rrd_create", "rrd_dump", "rrd_info", "rrd_last", and "rrd_fetch". AUTHOR Peter Stamfest <peter@stamfest.at> 1.10.3 2026-05-25 RRDTHREADS(1)
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