[Boost-users] Trouble with posix_time

Subject: [Boost-users] Trouble with posix_time
From: Davies, John (john.davies_at_[hidden])
Date: 2013-06-04 12:29:19

I'm trying to time part of my program and coming up with something I can't explain. I don't expect great accuracy with the sample code here. But I'd like to understand what is happening.

static boost::posix_time::ptime MillisecondsFromNow(int milliseconds)
{
    return(boost::posix_time::ptime(boost::posix_time::second_clock::universal_time()) +
                                                    boost::posix_time::milliseconds(milliseconds));
}

Code segment:

    nanosecond_type const twenty_seconds(20 * 1000000000LL);
    cpu_timer timer;
    long count = 0;
    while(true)
    {
        boost::thread::sleep(MillisecondsFromNow(1000));

        cpu_times const elapsed_times(timer.elapsed());
        nanosecond_type const elapsed(elapsed_times.wall);

        if (elapsed >= twenty_seconds)
        {
            break;
        }
        count++;
    }

    std::cout << count << '\n';

So I'm running for 20 seconds and delaying each time for a second. So I would expect to get output of 19, maybe 20 or 18. Instead I'm getting around 38-40

I've tried .system and .user and get different values. But never something close to 20.

This is on Windows.

___________________________________

John Davies
Contractor
Home Respiratory Care
Philips Home Healthcare Solutions
1740 Golden Mile Highway
Monroeville, PA 15146

Email: john.davies_at_[hidden]
Fax: [phone]

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