CODEWITHSUNDEEP
c++windowstimingasio
Lukas Hering
Lukas Hering

Reputation: 11

asio::high_resolution_timer gives inconsistent results on Windows

I'm writing a C++ application using asio for asynchronous networking and execution. In my application I want to be able to asynchronously call a function every 50 milliseconds with around one millisecond of error. I came up with this trivial example to illustrate what I am trying to do.

void timer_callback(asio::high_resolution_timer& timer, const std::error_code& error_code, long long t)
{
    auto current = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::high_resolution_clock::now().time_since_epoch()).count();
    auto diff = current - t;
    std::cout << diff << '\n';
    timer.expires_at(timer.expiry() + std::chrono::milliseconds(50));
    timer.async_wait([&timer, current](const std::error_code& error_code) { timer_callback(timer, error_code, current); });
}

int main()
{
    asio::io_context io_context;
    asio::high_resolution_timer timer(io_context);
    timer.expires_from_now(std::chrono::milliseconds(50));
    auto current = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::high_resolution_clock::now().time_since_epoch()).count();
    timer.async_wait([&timer, current](const std::error_code& error_code) { timer_callback(timer, error_code, current); });
    io_context.run();
}

I tried running the code on Linux and as expected the program outputted

50
50
50
50
50
50
50
50
50
50

However, when I tried compiling with MSVC and running the program on windows, I got the output

61
48
45
61
47
48
48
48
47
62

One would expect the windows program to also output the same results as the linux program since I am using std::chrono::high_resolution_clock for all of my timings. If someone could help explain these discrepancies, I would appreciate it.

Upvotes: 1

Views: 350

Answers (1)

Adam
Adam

Reputation: 952

Try calling timeBeginPeriod(1) somewhere near the the start of your program. That modifies the timer resolution to be ~1ms instead of ~15ms.

You can find some detailed discussion of the timer resolution at https://randomascii.wordpress.com/2020/10/04/windows-timer-resolution-the-great-rule-change/

Upvotes: 3

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