Parallel programming is about speeding up wall clock time, which is the real time that it takes a program to run. Unfortunately, some of the obvious wall clock timing routines provided by operating systems do not always work reliably across threads, because the hardware thread clocks are not synchronized. The library provides support for timing across threads. The routines are wrappers around operating services that we have verified as safe to use across threads.
For more complete information about compiler optimizations, see our Optimization Notice.