Uploaded image for project: 'Qt'
  1. Qt
  2. QTBUG-104012

QDateTime constructor performance regression when year is below epoch

    XMLWordPrintable

Details

    • Bug
    • Resolution: Out of scope
    • P2: Important
    • None
    • 6.3.0
    • Core: Date/Time
    • None
    • macOS, Windows
    • 21
    • 35d0f012e (dev), 0f4fb0bf2 (dev)
    • Foundation Sprint 87

    Description

      There seems to be a severe performance regression in how QDateTime handles dates with very low years (probably all years below epoch). This manifested in our application with severe stuttering.

      This code reproduces the problem quickly:

      QElapsedTimer timer;
timer.start();
for (qint64 i = 0; i < 1E7; i++)
    QDateTime someday(QDate(1, 1, 1), QTime(0, 0));
qDebug() << "Elapsed:" << timer.elapsed();

      This code takes a huge amount of time, I didn't even reach the end. If you replace the year with a value > 1970, then the time to complete is reasonable.

      I can reproduce this in MacOS and Windows. I cannot reproduce in Linux.

      Qt 5.15 does not seem to be affected.

      Attachments

        Issue Links

          relates to

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-109201 toString() in macOS' system locale is very slow

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Open

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-118759 [Regr:6.5->6.6] QDateTime comparison performance regression on macOS

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed

          Task - A task that needs to be done. QTBUG-56899 Add a static QTimeZone method to refresh system zone information

          • P3: Somewhat important - Should be fixed, but doesn't affect the release in any way.
          • Open
          No reviews matched the request. Check your Options in the drop-down menu of this sections header.

          Activity

            People

              Eddy Edward Welbourne
              luc4 Luca Carlon
              Vladimir Minenko Vladimir Minenko
              Alex Blasche Alex Blasche
              Votes:
              0 Vote for this issue
              Watchers:
              3 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved: