utl::sleep

utl::sleep is a header implementing precise sleep functions.

The main feature is a hybrid sleep function that uses a combination of system sleep, busy-waiting and some statistics to wait with an accuracy close to that of a spinlock, while keeping the thread free most of the time.

The idea is largely based on this excellent blogpost, which introduces the approach and presents a strong case for its robustness on most modern systems.

Definitions

template <class Rep, class Period> void system  (std::chrono::duration<Rep, Period> duration);
template <class Rep, class Period> void spinlock(std::chrono::duration<Rep, Period> duration);
template <class Rep, class Period> void hybrid  (std::chrono::duration<Rep, Period> duration);

Methods

template <class Rep, class Period> void system  (std::chrono::duration<Rep, Period> duration);
template <class Rep, class Period> void spinlock(std::chrono::duration<Rep, Period> duration);
template <class Rep, class Period> void hybrid  (std::chrono::duration<Rep, Period> duration);

3 sleep implementations functionally similar to std::this_thread::sleep_for(), with different precision / CPU time tradeoffs:

Sleep	Precision	CPU usage	Description
`system()`	Imprecise	~0%	Alias for `std::this_thread::sleep_for()`
`spinlock()`	Very precise	100%	Busy-waiting loop
`hybrid()`	Precise	~5%	Hybrid approach that loops short system sleep, statistically estimates its error on the fly and uses spinlock to finish the last few %

Examples

Comparing sleep precision

[ Run this code ]

using ms = std::chrono::duration<double, std::milli>;

constexpr int repeats        = 6;
constexpr ms  sleep_duration = ms(16.67);

const auto measure_time = [&](auto sleep_function) {
    for (int i = 0; i < repeats; ++i) {
        const auto start = std::chrono::steady_clock::now();
        sleep_function(sleep_duration);
        const auto end   = std::chrono::steady_clock::now();
        std::cout << ms(end - start).count() << " ms\n";
    }
};

std::cout << "Sleeping for 16.67 ms.\n";

std::cout << "\n--- sleep::system()   ---\n";
measure_time(utl::sleep::system<double, std::milli>);

std::cout << "\n--- sleep::spinlock() ---\n";
measure_time(utl::sleep::spinlock<double, std::milli>);

std::cout << "\n--- sleep::hybrid()   ---\n";
measure_time(utl::sleep::hybrid<double, std::milli>);

Output:

Sleeping for 16.67 ms.

--- sleep::system()   ---
16.7649 ms
16.7411 ms
16.7406 ms
16.7338 ms
16.7308 ms
16.7338 ms

--- sleep::spinlock() ---
16.6703 ms
16.6702 ms
16.6704 ms
16.6703 ms
16.6703 ms
16.6701 ms

--- sleep::hybrid()   ---
16.6723 ms
16.6723 ms
16.6725 ms
16.6723 ms
16.6721 ms
16.6721 ms

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