feat(app launch profiling): add app launch profiling

[armcknight]

This PR and those that follow will add the ability of the SDK to start the profiler as early as possible from our code in order to record profiling information during an app launch..

Internal design doc

Followed by #3558
Docs PR: getsentry/sentry-docs#8876

Major changes:

• persist traces/sampling rates to a file we can check on class load, before SentrySDK.startWithOptions is called

  • we store this in a new sentry path under Application Support, not caches as is used by SentryFileManager.sentryPath
  • starts a dedicated launch trace to attach the profile to

• add logic to SentryTracer to check the config file and control starting the profiler for launch; because SentryTracer is already the thing that manages SentryProfiler today, this seemed like the best location

• notes on some decisions

  • we decided not to use plist keys to enable this feature for now; we can iterate on it if we think profiling a post install/upgrade cold launch will be valuable (I think it would be) and after battle testing the existing logic
  • we considered using a root superclass to force a +[load] call order so we could start the profiler as early as possible, but decided against it for now, see ref: create root object as superclass for all SDK classes #3532
  • I considered exposing a method up through SentrySDK like startAppProfile so customers could do it from their own class load methods, but will save that for iterating; there's a timing experiment I'd like to do first
  • we tried using preexisting automatic transactions like ui.load but there are edge cases involved with it, and it doesn't cover all use cases like SwiftUI; so we decided instead to use dedicated traces for launch

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1217.18 ms	1238.24 ms	21.06 ms
Size	21.58 KiB	422.66 KiB	401.08 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
189b629	1211.16 ms	1224.30 ms	13.14 ms
98752f3	1240.61 ms	1259.80 ms	19.18 ms
06548c0	1225.58 ms	1244.70 ms	19.12 ms
f8fc36d	1226.31 ms	1247.80 ms	21.49 ms
dfde86d	1215.12 ms	1221.30 ms	6.18 ms
7c5d161	1224.38 ms	1249.66 ms	25.28 ms
0dfdaaa	1226.88 ms	1248.82 ms	21.94 ms
04c0c68	1223.22 ms	1251.24 ms	28.02 ms
2ce582e	1238.98 ms	1259.66 ms	20.68 ms
f2daa68	1211.14 ms	1217.53 ms	6.39 ms

App size

Revision	Plain	With Sentry	Diff
189b629	20.76 KiB	399.69 KiB	378.93 KiB
98752f3	20.76 KiB	435.09 KiB	414.33 KiB
06548c0	20.76 KiB	427.35 KiB	406.59 KiB
f8fc36d	20.76 KiB	419.70 KiB	398.94 KiB
dfde86d	21.58 KiB	414.57 KiB	392.99 KiB
7c5d161	20.76 KiB	414.44 KiB	393.68 KiB
0dfdaaa	20.76 KiB	434.56 KiB	413.79 KiB
04c0c68	22.85 KiB	414.09 KiB	391.24 KiB
2ce582e	22.85 KiB	410.97 KiB	388.12 KiB
f2daa68	21.58 KiB	418.40 KiB	396.82 KiB

Previous results on branch: armcknight/feat/launch-profiling

Startup times

Revision	Plain	With Sentry	Diff
55af12d	1229.06 ms	1244.85 ms	15.79 ms
97fc3fc	1203.63 ms	1211.80 ms	8.16 ms
a4122ec	1205.48 ms	1229.02 ms	23.54 ms
8512126	1232.21 ms	1253.60 ms	21.39 ms
7d8f64b	1214.90 ms	1230.56 ms	15.67 ms
2f41ea8	1194.29 ms	1204.35 ms	10.07 ms
a2498ae	1202.59 ms	1213.83 ms	11.24 ms
af0dbfd	1202.61 ms	1209.63 ms	7.02 ms
54c42ec	1208.63 ms	1224.35 ms	15.71 ms

App size

Revision	Plain	With Sentry	Diff
55af12d	21.58 KiB	421.23 KiB	399.65 KiB
97fc3fc	21.58 KiB	420.05 KiB	398.46 KiB
a4122ec	21.58 KiB	422.04 KiB	400.46 KiB
8512126	21.58 KiB	422.65 KiB	401.06 KiB
7d8f64b	21.58 KiB	422.15 KiB	400.57 KiB
2f41ea8	21.58 KiB	427.08 KiB	405.50 KiB
a2498ae	21.58 KiB	422.10 KiB	400.51 KiB
af0dbfd	21.58 KiB	422.10 KiB	400.52 KiB
54c42ec	21.58 KiB	422.66 KiB	401.08 KiB

[codecov]

Codecov Report

Attention: 75 lines in your changes are missing coverage. Please review.

Comparison is base (6e1452d) 89.348% compared to head (bb83d27) 89.223%.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3529       +/-   ##
=============================================
- Coverage   89.348%   89.223%   -0.126%     
=============================================
  Files          530       532        +2     
  Lines        58291     58691      +400     
  Branches     20917     21066      +149     
=============================================
+ Hits         52082     52366      +284     
- Misses        5183      5288      +105     
- Partials      1026      1037       +11     

Files	Coverage Δ
Sources/Sentry/Profiling/SentryProfilerState.mm	98.484% <100.000%> (+0.110%)	⬆️
Sources/Sentry/SentryHub.m	98.504% <100.000%> (-0.016%)	⬇️
Sources/Sentry/SentryLog.m	100.000% <100.000%> (ø)
Sources/Sentry/SentryOptions.m	97.613% <100.000%> (-0.036%)	⬇️
Sources/Sentry/SentryProfileTimeseries.mm	48.076% <100.000%> (+1.018%)	⬆️
Sources/Sentry/SentrySDK.m	90.697% <100.000%> (+0.259%)	⬆️
Sources/Sentry/SentrySamplerDecision.m	100.000% <100.000%> (ø)
Sources/Sentry/include/SentryInternalDefines.h	50.000% <100.000%> (+7.894%)	⬆️
...entryProfilerTests/SentryAppLaunchProfilingTests.m	100.000% <100.000%> (ø)
...SentryProfilerTests/SentryProfilerSwiftTests.swift	97.730% <100.000%> (-0.010%)	⬇️
... and 10 more

... and 15 files with indirect coverage changes

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[armcknight]

I fixed a build error by adding SentryProfilingConditionals.h to iOS-SwiftUI/TestHeaders, and Xcode made a whole bunch of changes in its project file. Not sure what's up with it. See 4866ffa

[philipphofmann]

I'm excited to see app start profiling moving forward 💪.

As this feature has a high risk of breaking things, I took a close look and added plenty of comments. I haven't completely reviewed all the code, as some comments could lead to a few changes that could make some of my comments outdated.

I will wait to review #3558 as changes here could also bubble up to it.

[brustolin]

Philipp did most of the heavy lifting in reviewing this, and it looks good.
I will give it another pass on Monday to understand everything and double-check.

[philipphofmann]

I found one more important issue. Apart from that LGTM.

[philipphofmann]

LGTM