rrdtool                                             RDTHREADS(1)



NAME
     rrdthreads - Provisions for linking the RD library to use
     in multi-threaded programs

SYNOPSIS
     Using librrd in multi-threaded programs requires some extra
     precautions, as the RD 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
     RD development to keep the library thread-safe.

     Currently only some RD 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:

     ]o   Link with librrdth instead of librrd (use "-lrrdth"
         when linking)

     ]o   Use the ""r"" functions instead of the normal API-
         functions

     ]o   Do not use any at-style time specifications. Parsing of
         such time specifications is terribly non-thread-safe.

     ]o   Never use non *"r" functions unless it is explicitly
         documented that the function is tread-safe.

     ]o   Every thread SHOULD call "rrdgetcontext()" before its
         first call to any "librrdth" 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.

     ]o   Always call "rrderrorclear()" before any call to the
         library. Otherwise the call might fail due to some
         earlier error.

     NOTES FOR RD CONTRIBUTORS

     Some precautions must be followed when developing RD from
     now on:

     ]o   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:

         ]o   Direct calls to "strerror()" must be avoided: use



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rrdtool                                             RDTHREADS(1)



             "rrdstrerror()" instead, it provides a per-thread
             error message.

         ]o   The "getpw*", "getgr*", "gethost*" function families
             (and some more "get*" functions) are not
             thread-safe: use the *"r" variants

         ]o   Time functions: "asctime", "ctime", "gmtime",
             "localtime": use *"r" variants

         ]o   "strtok": use "strtokr"

         ]o   "tmpnam": use "tmpnamr"

         ]o   Many others (lookup documentation)

     ]o   A header file named rrdisthreadsafe.h is provided
         that works with the GNU C-preprocessor to "poison" some
         of the most common non-thread-safe functions using the
         "#pragma GC poison" directive. Just include this header
         in source files you want to keep thread-safe.

     ]o   Do not introduce global variables!

         If you really, really have to use a global variable you
         may add a new field to the "rrdcontext" structure and
         modify rrderror.c, rrdthreadsafe.c and
         rrdnonthreadsafe.c

     ]o   Do not use "getopt" or "getoptlong" 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
         "rrdupdater" as an example.

     ]o   Do not use the "rrdparsetime" 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., "rrdcreate", but not in "rrdcreater")

     CURENTLY IMPLEMENTED THREAD SAFE FUNCTIONS

     Currently there exist thread-safe variants of "rrdupdate",
     "rrdcreate", "rrddump", "rrdinfo", "rrdlast", and
     "rrdfetch".




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rrdtool                                             RDTHREADS(1)



AUTHOR
     Peter Stamfest 





















































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