# man > rrdthreads(1)

[_RRDTHREADS_(1)](https://www.chedong.com/phpMan.php/man/RRDTHREADS/1/markdown)                                  rrdtool                                 [_RRDTHREADS_(1)](https://www.chedong.com/phpMan.php/man/RRDTHREADS/1/markdown)

## 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                                        2024-03-31                                [_RRDTHREADS_(1)](https://www.chedong.com/phpMan.php/man/RRDTHREADS/1/markdown)