rrdthreads - Man Page

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 there exist thread-safe variants of rrd_update, rrd_create, rrd_dump, rrd_info, rrd_last, and rrd_fetch.