获取时间的日差偶尔为负数

Question

我正在用perl编写一个面向对象的OpenGL框架，当我测量每帧之间的DeltaTime时，我遇到了一个奇怪的问题。增量时间似乎每隔一段时间（每~.5秒）变为负值。我不确定这是gettimeofday的问题，还是GLUT如何调用我的回调的问题，但这很烦人，因为它使我的精灵的运动每半秒稍微跳一下。

这是我的 glut 主循环函数：

# This is called everytime in the main glut loop
sub Tick
{
    my $this = shift;
    my ($now, $dt);
    $now = gettimeofday;
    $dt = $now - $this->{_oldTime};
    if ($dt < 0)
    {
        my $dterr;
        $dterr = $now - $this->{_oldErrorTime};
        print "WTF! We just encountered a time paradox! " . 
            "This function was last called $dt seconds ago...n" .
            "Current time: $now, Last call: $this->{_oldTime}n" .
            "We already encountered this error $dterr seconds ago.nn";
        $this->{_oldErrorTime} = $now;
    }
    $this->{_oldTime} = $now;
    $this->{FPS} = 1.0 / $dt;
    $this->Update($dt);
    $this->DrawFrame($dt);
}

这是输出：

跆拳道！我们刚刚遇到了一个时间悖论！上次调用此函数 -0.017144 9184417725秒前...当前时间：1340196716.27624，最后呼叫：1340196716.29339 我们已经遇到了此错误 0.482785940170288 秒前。

跆拳道！我们刚刚遇到了一个时间悖论！上次调用此函数 -0.013265 84815979秒前...当前时间：1340196716.74632，最后呼叫：1340196716.75959 我们已经遇到了此错误 0.470081090927124秒前。

跆拳道！我们刚刚遇到了一个时间悖论！上次调用此函数 -0.011317 9683685303秒前...当前时间：1340196717.21836，最后呼叫：1340196717.22968 我们已经遇到了此错误 0.472035884857178秒前。

跆拳道！我们刚刚遇到了一个时间悖论！上次调用此函数 -0.015201 0917663574秒前...当前时间：1340196717.68649，最后呼叫：1340196717.70169 我们已经遇到了此错误 0.468127012252808秒前。

Answer 1

您需要CLOCK_MONOTONIC，请参阅Time：：HiRes。

Answer 2

感谢你们的回答，我想出了这个跨平台单调的秒表功能：

use constant WIN32 =>   $^O eq "MSWin32";
our $QueryPerformanceCounter = undef;
our $QueryPerformanceFrequency = undef;
our $qpf = undef;
sub GetTime
{
    # Windows
    if (WIN32)
    {
        my ($count, @unpacked_count);
        require Win32::API;
        Win32::API->import();
        if (!$QueryPerformanceCounter || !$QueryPerformanceFrequency || !$qpf)
        {
            my ($freq, @unpacked_freq);
            $QueryPerformanceCounter = new Win32::API(
                "Kernel32", "QueryPerformanceCounter", [qw(P)], 'I')
            or Carp::croak("GLPerl::Utils::GetTime(): Failed to get QueryPerformanceCounter: " .
                Win32::FormatMessage(Win32::GetLastError()));
            $QueryPerformanceFrequency = new Win32::API(
                "Kernel32", "QueryPerformanceFrequency", [qw(P)], 'I')
            or Carp::croak("GLPerl::Utils::GetTime(): Failed to get QueryPerformanceFrequency: " .
                Win32::FormatMessage(Win32::GetLastError()));
            $freq = pack 'I2', 0;
            Carp::croak("GLPerl::Utils::GetTime(): QueryPerformanceFrequency call failed: " .
                Win32::FormatMessage(Win32::GetLastError()))
                unless ($QueryPerformanceFrequency->Call($freq));
            @unpacked_freq = reverse unpack 'I2', $freq;
            $qpf = $unpacked_freq[0] * 2**32 + $unpacked_freq[1];
        }
        $count = pack 'I2', 0;
        Carp::croak("GLPerl::Utils::GetTime(): QueryPerformanceCounter call failed: " .
            Win32::FormatMessage(Win32::GetLastError()))
            unless ($QueryPerformanceCounter->Call($count));
        @unpacked_count = reverse unpack 'I2', $count;
        return ($unpacked_count[0] * 2**32 + $unpacked_count[1]) / $qpf;
    }
    # Linux
    require Time::HiRes;
    Time::HiRes->import(qw(clock_gettime));
    eval "return clock_gettime(CLOCK_MONOTONIC);";
}