CODEWITHSUNDEEP
c++linuxtime
Nathan Doromal
Nathan Doromal

Reputation: 3547

How to make clock_gettime using CLOCK_REALTIME monotonic?

A problem with CLOCK_REALTIME is that it isn't monotonic and that time can potentially go backwards if a NTP sync occurred.

Would it be safe to do something like the following to make it monotonic?

struct timespec GetMonotonicTime()
{
    static struct timespec last = timespec();
    struct timespec ts;
    clock_gettime(CLOCK_REALTIME, &ts);
    last.tv_nsec = (last.tv_sec == ts.tv_sec) ? std::max(last.tv_nsec, ts.tv_nsec) : ts.tv_nsec;
    last.tv_sec = std::max(last.tv_sec, ts.tv_sec);

    return last;
}

Upvotes: 0

Views: 866

Answers (1)

Mark B
Mark B

Reputation: 96261

In addition to having problems if ever run in a multi-threaded envinronment your ns attribute will asymptote to 999999999 as time passes.

Linux provides CLOCK_MONOTONIC if that happens to be your platform (and it would satisfy your needs).

Upvotes: 1

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