Messung mit boost :: posix_time :: microsec_clock hat Fehler mehr als zehn Mikrosekunden?
Ich habe folgenden Code:
long long unsigned int GetCurrentTimestamp()
{
LARGE_INTEGER res;
QueryPerformanceCounter(&res);
return res.QuadPart;
}
long long unsigned int initalizeFrequency()
{
LARGE_INTEGER res;
QueryPerformanceFrequency(&res);
return res.QuadPart;
}
//start time stamp
boost::posix_time::ptime startTime = boost::posix_time::microsec_clock::local_time();
long long unsigned int start = GetCurrentTimestamp();
// ....
// execution that should be measured
// ....
long long unsigned int end = GetCurrentTimestamp();
boost::posix_time::ptime endTime = boost::posix_time::microsec_clock::local_time();
boost::posix_time::time_duration duration = endTime - startTime;
std::cout << "Duration by Boost posix: " << duration.total_microseconds() <<std::endl;
std::cout << "Processing time is " << ((end - start) * 1000000 / initalizeFrequency())
<< " microsec "<< std::endl;
Ergebnis dieses Codes ist
Duration by Boost posix: 0
Processing time is 24 microsec
Warum gibt es so große Unterschiede? Boost saugt so viel, wie es Mikrosekunden messen sollte, aber es misst Mikrosekunden mit Zehntel-Mikrosekunden-Fehler?