Try to avoid ConcurrentModificationError by not using a Future.forEach

[marandaneto]

📜 Description

Try to avoid ConcurrentModificationError by not using a Future.forEach.
I believe that the event loop has a sort of priority queue and maybe the future of finishing a late span is actually executed within the items of forEach (more priority in the scheduling) hence causing the ConcurrentModificationError, this is a hunch, I can't reproduce it either, let's go with a simple for loop for now.

💡 Motivation and Context

Closes #1256

💚 How did you test it?

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

[codecov]

Codecov Report

Base: 89.72% // Head: 88.78% // Decreases project coverage by -0.95% ⚠️

Coverage data is based on head (31de858) compared to base (c1bb00f).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1259      +/-   ##
==========================================
- Coverage   89.72%   88.78%   -0.95%     
==========================================
  Files         155      114      -41     
  Lines        5034     3666    -1368     
==========================================
- Hits         4517     3255    -1262     
+ Misses        517      411     -106     

Impacted Files	Coverage Δ
dart/lib/src/sentry_tracer.dart	93.95% <100.00%> (ø)
flutter/lib/src/flutter_sentry_attachment.dart
...t_processor/flutter_exception_event_processor.dart
...rc/screenshot/screenshot_attachment_processor.dart
...or/android_platform_exception_event_processor.dart
...ter/lib/src/integrations/on_error_integration.dart
flutter/lib/src/file_system_transport.dart
flutter/lib/src/sentry_native_channel.dart
.../lib/src/integrations/debug_print_integration.dart
flutter/lib/src/sentry_asset_bundle.dart
... and 32 more

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☔ View full report at Codecov.
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[marandaneto]

@ueman I added on the description what I think, but I can't reproduce or confirm it.

[github-actions]

Android Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	299.49 ms	361.24 ms	61.76 ms
Size	6.06 MiB	7.09 MiB	1.03 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
6325c3b	339.33 ms	409.86 ms	70.53 ms
9f9f94f	331.04 ms	368.92 ms	37.88 ms
559d28f	302.35 ms	339.53 ms	37.18 ms
5112c69	333.67 ms	363.74 ms	30.08 ms
521cfbf	332.78 ms	376.04 ms	43.26 ms
fbf42af	323.04 ms	365.09 ms	42.04 ms
3a69405	334.34 ms	369.19 ms	34.85 ms
6d7a391	331.94 ms	367.04 ms	35.10 ms
5aba417	355.78 ms	450.39 ms	94.61 ms
870f5eb	329.45 ms	369.29 ms	39.84 ms

App size

Revision	Plain	With Sentry	Diff
6325c3b	5.94 MiB	6.96 MiB	1.02 MiB
9f9f94f	5.94 MiB	6.95 MiB	1.01 MiB
559d28f	5.94 MiB	6.92 MiB	1001.70 KiB
5112c69	5.94 MiB	6.96 MiB	1.02 MiB
521cfbf	5.94 MiB	6.97 MiB	1.03 MiB
fbf42af	5.94 MiB	6.96 MiB	1.02 MiB
3a69405	5.94 MiB	6.95 MiB	1.01 MiB
6d7a391	5.94 MiB	6.95 MiB	1.01 MiB
5aba417	5.94 MiB	6.96 MiB	1.02 MiB
870f5eb	5.94 MiB	6.92 MiB	1005.77 KiB

[github-actions]

iOS Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1263.61 ms	1278.15 ms	14.53 ms
Size	8.09 MiB	9.07 MiB	1001.07 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
9811573	1259.78 ms	1278.33 ms	18.55 ms
f4cc744	1274.57 ms	1290.79 ms	16.22 ms
b728df4	1287.43 ms	1293.94 ms	6.51 ms
521cfbf	1258.94 ms	1275.18 ms	16.25 ms
21845e2	1279.37 ms	1298.81 ms	19.45 ms
a7acb24	1296.71 ms	1317.69 ms	20.98 ms
322aa66	1251.68 ms	1275.52 ms	23.84 ms
49a149b	1296.47 ms	1320.20 ms	23.73 ms
5603ab2	1268.47 ms	1280.73 ms	12.26 ms
b47809a	1252.61 ms	1278.57 ms	25.96 ms

App size

Revision	Plain	With Sentry	Diff
9811573	8.16 MiB	9.17 MiB	1.01 MiB
f4cc744	8.16 MiB	9.16 MiB	1.01 MiB
b728df4	8.15 MiB	9.15 MiB	1020.72 KiB
521cfbf	8.16 MiB	9.17 MiB	1.01 MiB
21845e2	8.15 MiB	9.12 MiB	991.34 KiB
a7acb24	8.16 MiB	9.17 MiB	1.01 MiB
322aa66	8.15 MiB	9.12 MiB	992.53 KiB
49a149b	8.15 MiB	9.12 MiB	986.26 KiB
5603ab2	8.15 MiB	9.12 MiB	990.57 KiB
b47809a	8.16 MiB	9.17 MiB	1.01 MiB

[ueman]

@ueman I added on the description what I think, but I can't reproduce or confirm it.

Thanks! The explanation seems plausible to me. Unfortunately, I also don't have any further insights. For me, it seems like there can happen some weird kind of race condition. The fix in this PR is something which solved it for, but I can't really explain why :/

It's really nagging me, that I can't figure this bug out.

Even if this doesn't fix the issue, this will improve the stacktrace of the thrown error and thus helpfully get us closer to figuring it out for real.

[krystofwoldrich]

LGTM 🚀