How Apple is making apps launch instantly in watchOS 3

With watchOS 3, Apple has made launching Watch apps near-instant. At least some apps. Absent new hardware with a faster computer-on-a-chip, the company had to use more brains than brawn to speed up the app experience. Here's how Apple did it.

How did Apple make Watch apps launch faster?

When Apple first released the Watch there were a lot of unknowns. So, the company was conservative. They used less memory than they had to, and they conserved battery life at the expense of everything else. Now, over a year since launch, Apple has a much better idea of the resources apps require, including power. So, the foot is pressing down on the pedal.

  1. Apple is spending some of that extra memory to cache your most important apps — the ones in the new "Dock". They stay resident, so there's nothing to load when you go to launch them. They simply pop to life.

  2. Apple is spending some of that extra battery life to enable just-in-time background refresh. That way, when an app pops back to life, its already up to date. Better, developers can alert an app that it should update, and that means when you browse through the Dock, it effectively becomes a Glance.

Taken together, the Dock replaces Glances, with your most important apps kept ready to launch at a moments notice, always updated with the best and latest data.

But... but... battery life?!

No worries. Turns out most people don't use a lot of different Watch apps, and don't use them in a way that significantly impacts battery life. So, while Apple is spending extra memory and extra power to enable instant apps, it's within the amount the company kept in reserve for initial release.

Bottom line, your app experience will be significantly better at very little "cost" to stability or power efficiency.

WWDC 2020


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