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)