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My project is a long time daemon service and need to busy check some conditions and take actions as soon as possible.

I want to use std::steady_clock to account the responsing time of my service and the busy/free duty proportion.

Everytime the service runs about in 20~100 microseconds, while the designing requirement is less than 160us. So I'm afraid that it would waste too much time to call steady_clock::now() frequently.

My question:

  1. Does steady_clock::now() make a syscall potentially? Would it result my program to be blocked irregularly for a long time(exceed 1ms)?
  2. Is there any better alternative method?
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  • 1
    This is likely to depend on specifics of kernel and library version, as well as hardware architecture. Commented Apr 23, 2024 at 16:45
  • 2
    If you want to know what's actually going on, then 1) read the source code. 2) use a profiler. 3) use a debugger. But, if I were to guess, I'd guess that on linux the gettimeofday or similar syscall would be called using the vdso, so would stay entirely in userspace - but that's just a guess. Commented Apr 23, 2024 at 16:45
  • 2
    Looks like it can: github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/src/c++11/… Commented Apr 23, 2024 at 16:53
  • "need to busy check some conditions and take actions" - why use a busy loop and not a condition variable? Commented Apr 23, 2024 at 17:03
  • 1
    @leon yeah, having a "long time daemon service" is sure to be great when it's cooking your CPU at 100% all the time... well, it's not my project. Commented Apr 23, 2024 at 23:39
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