Posted by Almaz Mingaleev – Software program Engineer and Masha Khokhlova – Technical Program Supervisor
It is that point of yr once more when many people transfer our clocks! Oh wait, your Android units did it mechanically, didn’t they? For Android customers residing in lots of international locations, this is probably not shocking. For instance, the US, EU and UK governments have not modified their time laws shortly*, so customers get up each morning to see the right time.
However, what occurs when time legal guidelines change? In the event you look globally, governments can and do change their time legal guidelines, generally yearly, and Android units must maintain as much as help our international consumer base.
To implement a area’s time laws, Android units must comply with a set of encoded guidelines. What are these guidelines? Let’s begin with why guidelines are wanted within the first place. Clearly, 7am in Los Angeles and 7am in London aren’t the identical time. Furthermore, if you’re in London and need to know the time in Los Angeles, you need to know what number of hours to subtract, and this isn’t mounted all year long**. So to inform native time (time your watches ought to present) it’s handy to have a reference clock that everyone on the planet agrees on. This clock is known as UTC, coordinated common time. Native time in London throughout winter matches UTC, throughout summer time it’s calculated by including one hour to UTC, normally known as UTC+1. For Los Angeles native time throughout summer time is UTC-8 (8 hours behind, UTC offset is -8 hours) and through winter it’s UTC-7 correspondingly. When a area modifications from one offset to a different, we name {that a} “transition”. Mixture of those offsets and guidelines when a transition occurs (equivalent to “final Sunday of March” or “first Sunday on or after eighth March”) defines a time zone. For some international locations, the time zone guidelines might be quite simple and primarily decided by their chosen UTC offset: “no transitions, we don’t transfer our clocks forwards and backwards”.
Governments can determine to vary the UTC offset for areas, introduce new time zone areas, or alter the day that daylight saving transitions happen. When governments do that, the time zone guidelines on each Android gadget must be up to date, in any other case the Android gadget will proceed to comply with the previous guidelines, which may result in an incorrect native time being proven to customers within the affected areas.
Android isn’t alone in needing to maintain monitor of this data. Thankfully, there’s a database supported by IANA (Web Assigned Numbers Authority) and maintained by a small group of volunteers often called the TZDB (Time Zone Database) which is used as a foundation for native timekeeping on most fashionable working programs. The TZDB comprises many of the data that Android wants.
There isn’t a schedule, however sometimes the TZDB releases a brand new replace 4-5 instances a yr. The Android workforce desires to launch updates that have an effect on its units as quickly as attainable.
How do these modifications attain your units?
1. Authorities indicators a regulation / decree.
2. Somebody lets IANA find out about these modifications
3. Relying on how a lot lead time was given and modifications introduced by different international locations IANA publishes a brand new TZDB launch.
4. The Android workforce incorporates the TZDB launch (together with a small quantity extra data we get hold of from associated tasks and derive ourselves) into our codebase.
5. We roll-out these updates to your units. How the roll-out occurs is determined by the kind and age of the Android gadget.
As you possibly can see, there are fairly a couple of steps. Making use of, testing and releasing an replace can take weeks. And it isn’t simply Android and different laptop working programs prefer it who have to take motion. There are normally telecoms, banks, airways and software program firms that must make changes to their very own programs and time tables. Residents of a rustic should be made conscious of modifications in order that they know what to anticipate, particularly if they’re utilizing older units which may not obtain crucial updates. And all of it takes time and might trigger issues for numerous individuals if it isn’t dealt with properly. The quantity of disruption attributable to a change is normally decided by the readability of the laws and spot interval that governments present. The TZDB volunteers are good at recognizing modifications, but it surely helps if the governments notify IANA immediately, particularly when it’s not clear the precise areas or present legal guidelines affected. Sadly, lots of the current time zone modifications got with a couple of month or much less discover time. Android has a set of suggestions for the way a lot discover to supply. Different working programs have comparable suggestions.
Android is continually evolving. Certainly one of such enhancements, Venture Mainline, launched in Android 10, has made an enormous distinction in how we replace essential components of the Android working system. It permits us to ship choose AOSP parts immediately by way of Google Play, making updates quicker than a full OTA replace and decreasing duplication of efforts carried out by every OEM.
From the start, time zone guidelines had been a element in Mainline, known as Time Zone Knowledge or tzdata module. This integration allowed us to react extra rapidly to government-mandated time zone modifications than earlier than. Nonetheless till 2023 tzdata updates had been nonetheless bundled with different Mainline modifications, generally resulting in testing complexities and slower deployment.
In 2023, we made additional investments in Mainline’s infrastructure and decoupled the tzdata module from the opposite parts. With this isolation, we gained the power to reply quickly to time zone laws modifications — typically releasing updates to Android customers exterior of the established launch cadence. Moreover, this transformation means time zone updates can attain a far better variety of Android units, making certain you as Android customers at all times see the right time.
So whereas your Android cellphone could not have the ability to restore that misplaced hour of sleep, you possibly can relaxation assured that it’ll present the correct time, because of volunteers and the Android workforce.
Curious in regards to the ever-changing world of time zones? Discover the IANA Time Zone Database and study extra about how time and time zones are managed on Android.
*In 2018-2019 there have been modifications in Alaska. This can be a blogpost, not a technical documentation!
**As a result of the US and UK apply their daylight saving modifications at totally different native instances and on totally different days of the yr.
