Php/docs/intro.hrtime
提供：Dev Guides
The HRTime extension implements a high resolution StopWatch class. It uses the best possible APIs on different platforms which brings resolution up to nanoseconds. It also makes possible to implement a custom stopwatch using low level ticks delivered by the underlaying APIs.
注意:
As of PHP 7.3.0 the related function hrtime() is part of the core.
