Cache UTC offset #3898
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@@ -1351,40 +1351,55 @@ void StelCore::moveObserverTo(const StelLocation& target, double duration, doubl | |
| emit locationChanged(getCurrentLocation()); | ||
| } | ||
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| QCache<size_t, qint64> StelCore::utcOffsetCache; | ||
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| double StelCore::getUTCOffset(const double JD) const | ||
| { | ||
| // This method takes a significant amount of time. Try to cache a few entries. | ||
| // All these elements can influence UTCOffset, so we must include them in the cache. | ||
| // Presumably, offset does not change during a minute, so we can exclude seconds here. | ||
| struct UTCOffsetHashData { | ||
| int year; | ||
| int month; | ||
| int day; | ||
| int hour; | ||
| int minute; | ||
| //int second; | ||
| StelLocation *loc; | ||
| QTimeZone *tz; | ||
| } u; | ||
| int second; | ||
| StelUtils::getDateTimeFromJulianDay(JD, &u.year, &u.month, &u.day, &u.hour, &u.minute, &second); | ||
| // as analogous to second statement in getJDFromDate, nkerr | ||
| if ( u.year <= 0 ) | ||
| { | ||
| u.year = u.year - 1; | ||
| } | ||
| //getTime/DateFromJulianDay returns UTC time, not local time | ||
| QDateTime universal(QDate(u.year, u.month, u.day), QTime(u.hour, u.minute, second), Qt::UTC); | ||
| if (!universal.isValid()) | ||
| { | ||
| //qWarning() << "JD " << QString("%1").arg(JD) << " out of bounds of QT help with GMT shift, using current datetime"; | ||
| // Assumes the GMT shift was always the same before year -4710 | ||
| // NOTE: QDateTime has no year 0, and therefore likely different leap year rules. | ||
| // Under which circumstances do we get invalid universal? | ||
| universal = QDateTime(QDate(-4710, u.month, u.day), QTime(u.hour, u.minute, second), Qt::UTC); | ||
| } | ||
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| #if defined(Q_OS_WIN) | ||
| if (abs(u.year)<3) | ||
| { | ||
| // Mitigate a QTBUG on Windows (GH #594). | ||
| // This bug causes offset to be MIN_INT in January to March, 1AD. | ||
| // We assume a constant offset in this remote history, | ||
| // so we construct yet another date to get a valid offset. | ||
| // Application of the named time zones is inappropriate in any case. | ||
| universal = QDateTime(QDate(3, u.month, u.day), QTime(u.hour, u.minute, second), Qt::UTC); | ||
| } | ||
| #endif | ||
| const StelLocation &loc = getCurrentLocation(); | ||
| const QString tzName(getCurrentTimeZone()); | ||
| const QTimeZone tz(tzName.toUtf8()); | ||
| // We must fight a bug in Qt6.2 on Linux. For some reason tz.isValid() is true even for our self-named zones LMST,LTST,system_default. | ||
| // We must use an intermediate Boolean which we set to false where needed. | ||
| bool tzValid=tz.isValid(); | ||
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@@ -1395,83 +1410,98 @@ double StelCore::getUTCOffset(const double JD) const | |
| qWarning() << "Invalid timezone: " << tzName; | ||
| } | ||
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| // Complete the cache object and hash it. | ||
| u.loc= & const_cast<StelLocation &>(loc); | ||
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Contributor
There was a problem hiding this comment. This is some ugliness here. Why do you keep the object by
Member
Author
There was a problem hiding this comment. This is what various warnings made me do.
Contributor
There was a problem hiding this comment. Well, this is the wrong way to read the warnings then :P They are supposed to make you improve the code, not equip it with kludges. |
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| u.tz = & const_cast<QTimeZone&>(tz); | ||
| size_t dateLocHash=qHash(&u); | ||
|
Contributor
There was a problem hiding this comment. Are you hashing a pointer to a local variable?..
Member
Author
There was a problem hiding this comment. Did I misunderstand the qHash() docs? Does this only hash the pointer, not its contents?
Contributor
There was a problem hiding this comment. Yes, you need a custom hash function for every custom data type. This may be of help. |
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| qint64 shiftInSeconds; | ||
| qint64 *shiftInSecondsCached=utcOffsetCache.object(dateLocHash); | ||
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| if (shiftInSecondsCached) // found in cache | ||
| { | ||
| shiftInSeconds=*shiftInSecondsCached; | ||
| } | ||
| else | ||
| { | ||
| if (tzName==L1S("system_default") || (loc.planetName==L1S("Earth") && !tzValid && !QString("LMST LTST").contains(tzName))) | ||
| { | ||
| QDateTime local = universal.toLocalTime(); | ||
| //Both timezones should be interpreted as UTC because secsTo() converts both | ||
| //times to UTC if their zones have different daylight saving time rules. | ||
| local.setTimeSpec(Qt::UTC); | ||
| shiftInSeconds = universal.secsTo(local); | ||
| if (abs(shiftInSeconds)>50000 || shiftInSeconds==INT_MIN) | ||
| { | ||
| qDebug() << "TZ system_default or invalid, At JD" << QString::number(JD, 'g', 11) << ", shift:" << shiftInSeconds; | ||
| } | ||
| } | ||
| else | ||
| { | ||
| // The first adoption of a standard time was on December 1, 1847 in Great Britain | ||
| if (tzValid && loc.planetName==L1S("Earth") && (JD>=StelCore::TZ_ERA_BEGINNING || getUseCustomTimeZone())) | ||
| { | ||
| if (getUseDST()) | ||
| shiftInSeconds = tz.offsetFromUtc(universal); | ||
| else | ||
| shiftInSeconds = tz.standardTimeOffset(universal); | ||
| if (abs(shiftInSeconds)>500000 || shiftInSeconds==INT_MIN) | ||
| { | ||
| // Something very strange has happened. The Windows-only clause above already mitigated GH #594. | ||
| // Trigger this with a named custom TZ like Europe/Stockholm. | ||
| // Then try to wheel back some date in January-March from year 10 to 0. Instead of year 1, it jumps to 70, | ||
| // an offset of INT_MIN | ||
| qWarning() << "ERROR TRAPPED! --- Please submit a bug report with this logfile attached."; | ||
| qWarning() << "TZ" << tz << "valid, but at JD" << QString::number(JD, 'g', 11) << ", shift:" << shiftInSeconds; | ||
| qWarning() << "Universal reference date: " << universal.toString(); | ||
| } | ||
| } | ||
| else | ||
| { | ||
| shiftInSeconds = qRound((loc.getLongitude()/15.f)*3600.f); // Local Mean Solar Time | ||
| } | ||
| if (tzName==L1S("LTST")) | ||
| shiftInSeconds += qRound(getSolutionEquationOfTime()*60); | ||
| } | ||
| //qDebug() << "ShiftInSeconds:" << shiftInSeconds; | ||
| #ifdef Q_OS_WIN | ||
| // A dirty hack for report: https://github.com/Stellarium/stellarium/issues/686 | ||
| // TODO: switch to IANA TZ on all operating systems | ||
| if (tzName==L1S("Europe/Volgograd")) | ||
| shiftInSeconds = 4*3600; // UTC+04:00 | ||
| #endif | ||
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| // Extraterrestrial: Either use the configured Terrestrial timezone, or even a pseudo-LMST based on planet's rotation speed? | ||
| if (loc.planetName!=L1S("Earth")) | ||
| { | ||
| if (tzValid && (JD>=StelCore::TZ_ERA_BEGINNING || getUseCustomTimeZone())) | ||
| { | ||
| if (getUseDST()) | ||
| shiftInSeconds = tz.offsetFromUtc(universal); | ||
| else | ||
| shiftInSeconds = tz.standardTimeOffset(universal); | ||
| if (shiftInSeconds==INT_MIN) // triggered error | ||
| { | ||
| // Something very strange has happened. The Windows-only clause above already mitigated GH #594. | ||
| // Trigger this with a named custom TZ like Europe/Stockholm. | ||
| // Then try to wheel back some date in January-March from year 10 to 0. Instead of year 1, it jumps to 70, | ||
| // an offset of INT_MIN | ||
| qWarning() << "ERROR TRAPPED! --- Please submit a bug report with this logfile attached."; | ||
| qWarning() << "TZ" << tz << "valid, but at JD" << QString::number(JD, 'g', 11) << ", shift:" << shiftInSeconds; | ||
| qWarning() << "Universal reference date: " << universal.toString(); | ||
| } | ||
| } | ||
| else | ||
| { | ||
| // TODO: This should give "mean solar time" for any planet. | ||
| // Combine rotation and orbit, or (for moons) rotation and orbit of parent planet. | ||
| // LTST is even worse, needs equation of time for other planets. | ||
| shiftInSeconds = 0; // For now, give UT | ||
| } | ||
| } | ||
| shiftInSecondsCached = new qint64(shiftInSeconds); | ||
| utcOffsetCache.insert(dateLocHash, shiftInSecondsCached); | ||
| } | ||
| return shiftInSeconds / 3600.0; | ||
| } | ||
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Looks like an unsafe assumption to me. What is the cost of keeping the seconds?
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updates every second, not every minute.