How to sleep until next Sunday

Question

How can I sleep until next Sunday using boost? Can i convert boost::gregorian::date object to something that boost::this_thread::sleep_until can handle? Is it possible?

#include <boost/date_time.hpp>

int main()
{
    boost::gregorian::date current_date(boost::gregorian::day_clock::local_day());
    boost::gregorian::greg_weekday next_sunday_date(boost::gregorian::Sunday);
    boost::gregorian::date next_weekday_date = next_weekday(current_date, next_sunday_date);
    // ...
}

Answer 1

Here's what I came up with.

Note that I made the code generally more readable. This is important, not just for future maintenance, but also because it will allow you to "see the forest for the trees" - in turn allowing you to remember the important concepts mentally.

At least, that helps me.

Edit DyP contributed a way to use sleep_until (which would behave more accurately in rare circumstances, e.g. where the clock would change during the sleep).

#include <boost/date_time.hpp>
#include <boost/date_time/time_clock.hpp>
#include <iostream>

#include <thread>
#include <chrono>

int main()
{
    using namespace boost::gregorian;
    using boost::posix_time::ptime;
    using clock = boost::posix_time::microsec_clock; // or: boost::posix_time::second_clock;

    auto today       = date(day_clock::local_day());
    auto at_sunday   = greg_weekday(Sunday);
    auto next_sunday = next_weekday(today, at_sunday);

#if 1
    auto as_tm         = to_tm(next_sunday);
    auto as_time_t     = mktime(&as_tm);
    auto as_time_point = std::chrono::system_clock::from_time_t(as_time_t);

    std::this_thread::sleep_until(as_time_point);
#else
    auto duration = (ptime(next_sunday) - clock::local_time());
    auto msecs    = duration.total_milliseconds();
    std::cout << msecs << "\n";

    std::this_thread::sleep_for(std::chrono::milliseconds(msecs));
#endif
}

See it compiling on Coliru (obviously times out)

Answer 2

This sounds unstable. What if the user turns the computer off or goes into hibernation, or just does a restart?

I would do this in one of two ways:

1. Add a scheduled task(or whatever the windows/osx terminology is) / cronjob (linux) and set it to run on Sunday.

2. Add it to autostart and periodically(once per 10/30/60 minutes) check if it's Sunday.

Both ways handle restart/shut off/hibernation better than sleeping for 5 days.