This function returns the number of seconds (as a floating point number) that a function has run during all complete invocations of the function while profiling has been active. The number of seconds is measured using the QNX 4 tick clock, and thus represents elapsed time rather than CPU time, with a granularity of one tick (typically 10ms). Invocations of the function which have not completed at the time of the call to function_runtime are not included in the calculation.