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RRDTHREADS(1)			    rrdtool			 RRDTHREADS(1)

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

       Using librrd in multi-threaded programs requires some extra precau
       tions, 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.

       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.


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

	  Only use thread-safe functions in library code. Many often used
	   libc functions arent thread-safe. Take care in the following situ
	   ations or when using the following library functions:

	      Direct calls to "strerror()" must be avoided: use "rrd_str
	       error()" 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" vari

	      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

	  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

	   "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 "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_cre


       Currently there exist thread-safe variants of "rrd_update", "rrd_cre
       ate", "rrd_dump", "rrd_info" and "rrd_last".

       Peter Stamfest 

1.2.15				  2006-07-14			 RRDTHREADS(1)

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