How not to hog CPU while waiting for some event?

Question

I would like to write some code that wakes up on (or sleep until) some event.

I have a piece of code that sleeps until some event happens, such as when alarmed by a clock.

Pseudo code:

int main() {
  TimePoint someTp("3PM");
  std::this_thread::sleep_until(someTP);
}

This is my current implementation, but this hogs about 10% of my CPU power. I think my design is flawed, is there any better solution for this? Many thanks in advance!

Answer 1

The problem is in the implementation of std::this_thread:sleep_until(..) which calls sleep_for(..), which calls nanosleep().

(See the gnu sources, line 271.)

See the following Stackoverflow questions:

• nanosleep high cpu usage? (Linux high-cpu issue calling nanosleep.)
• boost::this_thread::sleep() vs. nanosleep()?

You don't appear to need the high resolution of nanosleep(). You might write your own solution with a permissive open source license, and call sleep() instead of nanosleep().

If you do need sub-second resolution, I recommend the technique of calling select() rather than nanosleep(). select() is designed to block very efficiently for sub-second delays, and the timeout parameter is respected accurately enough by most operating systems that it is useful for sub-second timing while yielding the CPU.

You can even create a socket for the purpose of passing to select(), in theerror_fds parameter, where the socket can be used as a cross-thread "signal" when it is passed to close() and becomes an "error" state socket.