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, as the RRD library in its
       original form was not thread-safe at all. This document describes requirements and pitfalls on the way to
       use the multi-threaded version of librrd in your own programs. It also gives hints for future RRD
       development to keep the library thread-safe.

       Currently only some RRD operations are implemented in a thread-safe way. They all end in the usual ""_r""
       suffix.

DESCRIPTION

       In order to use librrd in multi-threaded programs you must:

       •   Link with librrd_th instead of librrd (use "-lrrd_th" 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 tread-safe.

       •   Every thread SHOULD call "rrd_get_context()" before its first call to  any  "librrd_th"  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_error_clear()" 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()" 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  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 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")

   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>

1.7.2                                              2022-03-17                                      RRDTHREADS(1)