Report pre-warmed app starts

[philipphofmann]

📜 Description

Report pre-warmed app starts by dropping the first app start spans if pre-warming paused during these steps.
This approach will shorten the app start duration, but it represents the duration a user has to wait after clicking
the app icon until the app is responsive. We report the app start type in the appContext, so Sentry can make
changes to the UI for prewarmed app starts.

As it's really hard to test this properly, I added an experimental feature flag so we can get feedback first before making it GA. I plan to remove the feature flag in the future if we are sure this works correctly.

Docs PR getsentry/sentry-docs#5762

Normal app start with all spans

Pre-warmed with dropped spans

App Context

💡 Motivation and Context

Fixes GH-1897

💚 How did you test it?

Unit tests and simulators

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the docs if needed
• Review from the native team if needed
• No breaking changes

🔮 Next steps

[github-actions]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

---

"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1208.16 ms	1220.71 ms	12.55 ms
Size	20.75 KiB	369.28 KiB	348.52 KiB

Baseline results on branch: master

Startup times

Revision	Plain	With Sentry	Diff
347a8e9	1243.50 ms	1265.90 ms	22.40 ms
8b040e4	1234.76 ms	1244.71 ms	9.95 ms
bdfccaa	1202.83 ms	1228.96 ms	26.13 ms
075911d	1256.73 ms	1271.22 ms	14.49 ms
5025d2e	1248.52 ms	1251.72 ms	3.20 ms
4a0c282	1228.60 ms	1250.74 ms	22.14 ms
d73ebd0	1200.83 ms	1236.10 ms	35.27 ms
c2a9b60	1222.10 ms	1240.62 ms	18.52 ms
5025d2e	1245.14 ms	1268.58 ms	23.44 ms
6177f2d	1206.55 ms	1226.20 ms	19.65 ms

App size

Revision	Plain	With Sentry	Diff
347a8e9	20.51 KiB	333.16 KiB	312.65 KiB
8b040e4	20.50 KiB	333.54 KiB	313.04 KiB
bdfccaa	20.50 KiB	361.80 KiB	341.29 KiB
075911d	20.51 KiB	332.90 KiB	312.39 KiB
5025d2e	20.51 KiB	331.79 KiB	311.28 KiB
4a0c282	20.51 KiB	333.10 KiB	312.60 KiB
d73ebd0	20.50 KiB	365.18 KiB	344.68 KiB
c2a9b60	20.50 KiB	333.54 KiB	313.04 KiB
5025d2e	20.51 KiB	331.79 KiB	311.28 KiB
6177f2d	20.51 KiB	332.90 KiB	312.40 KiB

Previous results on branch: fix/report-prewarmed-app-starts

Startup times

Revision	Plain	With Sentry	Diff
6cf9be6	1216.21 ms	1247.00 ms	30.79 ms
f8f4884	1189.00 ms	1233.60 ms	44.60 ms
8136d66	1239.44 ms	1266.82 ms	27.38 ms
55ab513	1219.20 ms	1254.55 ms	35.35 ms
58f3415	1235.48 ms	1265.36 ms	29.88 ms
746f90b	1235.90 ms	1250.02 ms	14.12 ms
54bfce4	1245.84 ms	1271.64 ms	25.80 ms

App size

Revision	Plain	With Sentry	Diff
6cf9be6	20.75 KiB	369.27 KiB	348.52 KiB
f8f4884	20.75 KiB	369.18 KiB	348.42 KiB
8136d66	20.75 KiB	369.18 KiB	348.43 KiB
55ab513	20.75 KiB	369.28 KiB	348.52 KiB
58f3415	20.75 KiB	369.27 KiB	348.52 KiB
746f90b	20.75 KiB	369.18 KiB	348.42 KiB
54bfce4	20.75 KiB	368.59 KiB	347.84 KiB

[armcknight]

Looks good. Would you mind writing some comments to explain some of the constant int values in some of the tests, like here and here?

[armcknight]

If this 500 is meant to test exceeding the maximum launch duration, we could convert that macro to a constant and expose it to this test.

[philipphofmann]

It depends on fixture.appStartDuration. Good point, I changed it.

[brustolin]

LGTM