/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- * vim: set ts=8 sts=2 et sw=2 tw=80: * This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ #ifndef vm_DateTime_h #define vm_DateTime_h #include "mozilla/Assertions.h" #include "mozilla/Attributes.h" #include "mozilla/UniquePtr.h" #include "mozilla/Unused.h" #include #include "js/Utility.h" #include "threading/ExclusiveData.h" #if JS_HAS_INTL_API && !MOZ_SYSTEM_ICU # include "unicode/uversion.h" U_NAMESPACE_BEGIN class TimeZone; U_NAMESPACE_END #endif /* JS_HAS_INTL_API && !MOZ_SYSTEM_ICU */ namespace js { /* Constants defined by ES5 15.9.1.10. */ constexpr double HoursPerDay = 24; constexpr double MinutesPerHour = 60; constexpr double SecondsPerMinute = 60; constexpr double msPerSecond = 1000; constexpr double msPerMinute = msPerSecond * SecondsPerMinute; constexpr double msPerHour = msPerMinute * MinutesPerHour; /* ES5 15.9.1.2. */ constexpr double msPerDay = msPerHour * HoursPerDay; /* * Additional quantities not mentioned in the spec. Be careful using these! * They aren't doubles and aren't defined in terms of all the other constants. * If you need constants that trigger floating point semantics, you'll have to * manually cast to get it. */ constexpr unsigned SecondsPerHour = 60 * 60; constexpr unsigned SecondsPerDay = SecondsPerHour * 24; constexpr double StartOfTime = -8.64e15; constexpr double EndOfTime = 8.64e15; extern bool InitDateTimeState(); extern void FinishDateTimeState(); enum class ResetTimeZoneMode : bool { DontResetIfOffsetUnchanged, ResetEvenIfOffsetUnchanged, }; /** * Engine-internal variant of JS::ResetTimeZone with an additional flag to * control whether to forcibly reset all time zone data (this is the default * behavior when calling JS::ResetTimeZone) or to try to reuse the previous * time zone data. */ extern void ResetTimeZoneInternal(ResetTimeZoneMode mode); /** * ICU's default time zone, used for various date/time formatting operations * that include the local time in the representation, is allowed to go stale * for unfortunate performance reasons. Call this function when an up-to-date * default time zone is required, to resync ICU's default time zone with * reality. */ extern void ResyncICUDefaultTimeZone(); /** * Stores date/time information, particularly concerning the current local * time zone, and implements a small cache for daylight saving time offset * computation. * * The basic idea is premised upon this fact: the DST offset never changes more * than once in any thirty-day period. If we know the offset at t_0 is o_0, * the offset at [t_1, t_2] is also o_0, where t_1 + 3_0 days == t_2, * t_1 <= t_0, and t0 <= t2. (In other words, t_0 is always somewhere within a * thirty-day range where the DST offset is constant: DST changes never occur * more than once in any thirty-day period.) Therefore, if we intelligently * retain knowledge of the offset for a range of dates (which may vary over * time), and if requests are usually for dates within that range, we can often * provide a response without repeated offset calculation. * * Our caching strategy is as follows: on the first request at date t_0 compute * the requested offset o_0. Save { start: t_0, end: t_0, offset: o_0 } as the * cache's state. Subsequent requests within that range are straightforwardly * handled. If a request for t_i is far outside the range (more than thirty * days), compute o_i = dstOffset(t_i) and save { start: t_i, end: t_i, * offset: t_i }. Otherwise attempt to *overextend* the range to either * [start - 30d, end] or [start, end + 30d] as appropriate to encompass * t_i. If the offset o_i30 is the same as the cached offset, extend the * range. Otherwise the over-guess crossed a DST change -- compute * o_i = dstOffset(t_i) and either extend the original range (if o_i == offset) * or start a new one beneath/above the current one with o_i30 as the offset. * * This cache strategy results in 0 to 2 DST offset computations. The naive * always-compute strategy is 1 computation, and since cache maintenance is a * handful of integer arithmetic instructions the speed difference between * always-1 and 1-with-cache is negligible. Caching loses if two computations * happen: when the date is within 30 days of the cached range and when that * 30-day range crosses a DST change. This is relatively uncommon. Further, * instances of such are often dominated by in-range hits, so caching is an * overall slight win. * * Why 30 days? For correctness the duration must be smaller than any possible * duration between DST changes. Past that, note that 1) a large duration * increases the likelihood of crossing a DST change while reducing the number * of cache misses, and 2) a small duration decreases the size of the cached * range while producing more misses. Using a month as the interval change is * a balance between these two that tries to optimize for the calendar month at * a time that a site might display. (One could imagine an adaptive duration * that accommodates near-DST-change dates better; we don't believe the * potential win from better caching offsets the loss from extra complexity.) */ class DateTimeInfo { static ExclusiveData* instance; friend class ExclusiveData; friend bool InitDateTimeState(); friend void FinishDateTimeState(); DateTimeInfo(); ~DateTimeInfo(); static auto acquireLockWithValidTimeZone() { auto guard = instance->lock(); if (guard->timeZoneStatus_ != TimeZoneStatus::Valid) { guard->updateTimeZone(); } return guard; } public: // The spec implicitly assumes DST and time zone adjustment information // never change in the course of a function -- sometimes even across // reentrancy. So make critical sections as narrow as possible. /** * Get the DST offset in milliseconds at a UTC time. This is usually * either 0 or |msPerSecond * SecondsPerHour|, but at least one exotic time * zone (Lord Howe Island, Australia) has a fractional-hour offset, just to * keep things interesting. */ static int32_t getDSTOffsetMilliseconds(int64_t utcMilliseconds) { auto guard = acquireLockWithValidTimeZone(); return guard->internalGetDSTOffsetMilliseconds(utcMilliseconds); } /** * The offset in seconds from the current UTC time to the current local * standard time (i.e. not including any offset due to DST) as computed by the * operating system. */ static int32_t utcToLocalStandardOffsetSeconds() { auto guard = acquireLockWithValidTimeZone(); return guard->utcToLocalStandardOffsetSeconds_; } #if JS_HAS_INTL_API && !MOZ_SYSTEM_ICU enum class TimeZoneOffset { UTC, Local }; /** * Return the time zone offset, including DST, in milliseconds at the * given time. The input time can be either at UTC or at local time. */ static int32_t getOffsetMilliseconds(int64_t milliseconds, TimeZoneOffset offset) { auto guard = acquireLockWithValidTimeZone(); return guard->internalGetOffsetMilliseconds(milliseconds, offset); } /** * Copy the display name for the current time zone at the given time, * localized for the specified locale, into the supplied buffer. If the * buffer is too small, an empty string is stored. The stored display name * is null-terminated in any case. */ static bool timeZoneDisplayName(char16_t* buf, size_t buflen, int64_t utcMilliseconds, const char* locale) { auto guard = acquireLockWithValidTimeZone(); return guard->internalTimeZoneDisplayName(buf, buflen, utcMilliseconds, locale); } #else /** * Return the local time zone adjustment (ES2019 20.3.1.7) as computed by * the operating system. */ static int32_t localTZA() { return utcToLocalStandardOffsetSeconds() * msPerSecond; } #endif /* JS_HAS_INTL_API && !MOZ_SYSTEM_ICU */ private: // The two methods below should only be called via js::ResetTimeZoneInternal() // and js::ResyncICUDefaultTimeZone(). friend void js::ResetTimeZoneInternal(ResetTimeZoneMode); friend void js::ResyncICUDefaultTimeZone(); static void resetTimeZone(ResetTimeZoneMode mode) { auto guard = instance->lock(); guard->internalResetTimeZone(mode); } static void resyncICUDefaultTimeZone() { auto guard = acquireLockWithValidTimeZone(); mozilla::Unused << guard; } struct RangeCache { // Start and end offsets in seconds describing the current and the // last cached range. int64_t startSeconds, endSeconds; int64_t oldStartSeconds, oldEndSeconds; // The current and the last cached offset in milliseconds. int32_t offsetMilliseconds; int32_t oldOffsetMilliseconds; void reset(); void sanityCheck(); }; enum class TimeZoneStatus : uint8_t { Valid, NeedsUpdate, UpdateIfChanged }; TimeZoneStatus timeZoneStatus_; /** * The offset in seconds from the current UTC time to the current local * standard time (i.e. not including any offset due to DST) as computed by the * operating system. * * Cached because retrieving this dynamically is Slow, and a certain venerable * benchmark which shall not be named depends on it being fast. * * SpiderMonkey occasionally and arbitrarily updates this value from the * system time zone to attempt to keep this reasonably up-to-date. If * temporary inaccuracy can't be tolerated, JSAPI clients may call * JS::ResetTimeZone to forcibly sync this with the system time zone. * * In most cases this value is consistent with the raw time zone offset as * returned by the ICU default time zone (`icu::TimeZone::getRawOffset()`), * but it is possible to create cases where the operating system default time * zone differs from the ICU default time zone. For example ICU doesn't * support the full range of TZ environment variable settings, which can * result in returning a different time zone than what's returned by * ICU. One example is "TZ=WGT3WGST,M3.5.0/-2,M10.5.0/-1", where * returns -3 hours as the local offset, but ICU flat out rejects the TZ value * and instead infers the default time zone via "/etc/localtime" (on Unix). * This offset can also differ from ICU when the operating system and ICU use * different tzdata versions and the time zone rules of the current system * time zone have changed. Or, on Windows, when the Windows default time zone * can't be mapped to a IANA time zone, see for example * . * * When ICU is exclusively used for time zone computations, that means when * |JS_HAS_INTL_API && !MOZ_SYSTEM_ICU| is true, this field is only used to * detect system default time zone changes. It must not be used to convert * between local and UTC time, because, as outlined above, this could lead to * different results when compared to ICU. */ int32_t utcToLocalStandardOffsetSeconds_; RangeCache dstRange_; // UTC-based ranges #if JS_HAS_INTL_API && !MOZ_SYSTEM_ICU // ICU's TimeZone class is currently only available through the C++ API, // see . Due to the // lack of a stable ABI in C++, we therefore need to restrict this class // to only use ICU when we use our in-tree ICU copy. // Use the full date-time range when we can use ICU's TimeZone support. static constexpr int64_t MinTimeT = static_cast(StartOfTime / msPerSecond); static constexpr int64_t MaxTimeT = static_cast(EndOfTime / msPerSecond); RangeCache utcRange_; // localtime-based ranges RangeCache localRange_; // UTC-based ranges /** * The current ICU time zone. Lazily constructed to avoid potential I/O * access when initializing this class. */ mozilla::UniquePtr timeZone_; /** * Cached names of the standard and daylight savings display names of the * current time zone for the default locale. */ JS::UniqueChars locale_; JS::UniqueTwoByteChars standardName_; JS::UniqueTwoByteChars daylightSavingsName_; #else // Restrict the data-time range to the minimum required time_t range as // specified in POSIX. Most operating systems support 64-bit time_t // values, but we currently still have some configurations which use // 32-bit time_t, e.g. the ARM simulator on 32-bit Linux (bug 1406993). // Bug 1406992 explores to use 64-bit time_t when supported by the // underlying operating system. static constexpr int64_t MinTimeT = 0; /* time_t 01/01/1970 */ static constexpr int64_t MaxTimeT = 2145830400; /* time_t 12/31/2037 */ #endif /* JS_HAS_INTL_API && !MOZ_SYSTEM_ICU */ static constexpr int64_t RangeExpansionAmount = 30 * SecondsPerDay; void internalResetTimeZone(ResetTimeZoneMode mode); void updateTimeZone(); void internalResyncICUDefaultTimeZone(); int64_t toClampedSeconds(int64_t milliseconds); using ComputeFn = int32_t (DateTimeInfo::*)(int64_t); /** * Get or compute an offset value for the requested seconds value. */ int32_t getOrComputeValue(RangeCache& range, int64_t seconds, ComputeFn compute); /** * Compute the DST offset at the given UTC time in seconds from the epoch. * (getDSTOffsetMilliseconds attempts to return a cached value from the * dstRange_ member, but in case of a cache miss it calls this method.) */ int32_t computeDSTOffsetMilliseconds(int64_t utcSeconds); int32_t internalGetDSTOffsetMilliseconds(int64_t utcMilliseconds); #if JS_HAS_INTL_API && !MOZ_SYSTEM_ICU /** * Compute the UTC offset in milliseconds for the given local time. Called * by internalGetOffsetMilliseconds on a cache miss. */ int32_t computeUTCOffsetMilliseconds(int64_t localSeconds); /** * Compute the local time offset in milliseconds for the given UTC time. * Called by internalGetOffsetMilliseconds on a cache miss. */ int32_t computeLocalOffsetMilliseconds(int64_t utcSeconds); int32_t internalGetOffsetMilliseconds(int64_t milliseconds, TimeZoneOffset offset); bool internalTimeZoneDisplayName(char16_t* buf, size_t buflen, int64_t utcMilliseconds, const char* locale); icu::TimeZone* timeZone(); #endif /* JS_HAS_INTL_API && !MOZ_SYSTEM_ICU */ }; } /* namespace js */ #endif /* vm_DateTime_h */