_R_R_D_T_H_R_E_A_D_S(1)                       rrdtool                      _R_R_D_T_H_R_E_A_D_S(1)

NNAAMMEE
       rrdthreads - Provisions for linking the RRD library to use in
       multi-threaded programs

SSYYNNOOPPSSIISS
       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, _l_i_b_r_r_d is thread-safe and no separate
       thread-specific library is needed.

DDEESSCCRRIIPPTTIIOONN
       In order to use librrd in multi-threaded programs you must:

       •   Link with _l_i_b_r_r_d (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
           specifications 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.

   NNOOTTEESS FFOORR RRRRDD CCOONNTTRRIIBBUUTTOORRSS
       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()
               instead, 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 _r_r_d___i_s___t_h_r_e_a_d___s_a_f_e_._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 _r_r_d___e_r_r_o_r_._c,
           _r_r_d___t_h_r_e_a_d___s_a_f_e_._c and _r_r_d___n_o_n___t_h_r_e_a_d___s_a_f_e_._c

       •   Do not use "getopt" or "getopt_long" in *"_r" (neither directly nor
           indirectly).

           "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
           designed to be thread-safe, like in functions wrapping the "_r"
           version of some operation (e.g., "rrd_create", but not in
           "rrd_create_r")

   CCUURRRREENNTTLLYY IIMMPPLLEEMMEENNTTEEDD TTHHRREEAADD SSAAFFEE FFUUNNCCTTIIOONNSS
       Currently there exist thread-safe variants of "rrd_update",
       "rrd_create", "rrd_dump", "rrd_info", "rrd_last", and "rrd_fetch".

AAUUTTHHOORR
       Peter Stamfest <peter@stamfest.at>

1.10.2                            2026-06-08                     _R_R_D_T_H_R_E_A_D_S(1)
