In this test, 'cpuNanos' occasionally returns '0' instead of a positive integer.

I believe this may happen if the OS migrates a thread to a different CPU, which could lead to bogus results, per the man page:

The CLOCK_PROCESS_CPUTIME_ID and CLOCK_THREAD_CPUTIME_ID clocks are realized on many platforms using timers from the CPUs (TSC on i386, AR.ITC on Itanium). These registers may differ between CPUs and as a consequence these clocks may return bogus results if a process is migrated to another CPU.

The test failures have always resulted in values of exactly 0 elapsed time (never negative) which suggests something else could be going on as well.

Print more diagnostic information when operations return 0 cpuNanos.