[3] [[Mac OS X]] では [CODE[clock_gettime]] が実装されていないようです。

[1] [CITE[objective c - Monotonic clock on OSX - Stack Overflow]]
([TIME[2016-07-25 18:33:37 +09:00]])
<http://stackoverflow.com/questions/11680461/monotonic-clock-on-osx>

[2] [CITE@en[Issue 1159 - nativeclient - CLOCK_MONOTONIC is not defined - Monorail]]
([TIME[2016-07-25 18:36:10 +09:00]])
<https://bugs.chromium.org/p/nativeclient/issues/detail?id=1159>