fix: Crash in SentryTracer when cancelling timer

[philipphofmann]

📜 Description

The SentryTracer starts the timer for the deadline on the main thread and invalidates the timer, not necessarily on the main thread, but invalidate has to be called on the same thread on which the timer was started. This is fixed by starting and invalidating the NSTimer on the main thread.

💡 Motivation and Context

Fixes GH-3320

💚 How did you test it?

It isn't straightforward to reproduce the EXC_BAD_ACCESS in the SentryTracer, cause violating calling invalidate on a different thread doesn't necessarily lead to crashes, see Apple Docs. Unit tests.

📝 Checklist

You have to check all boxes before merging:

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1233.83 ms	1264.29 ms	30.46 ms
Size	22.85 KiB	411.37 KiB	388.52 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d257eb9	1226.08 ms	1256.54 ms	30.46 ms
89bc37d	1228.20 ms	1257.10 ms	28.90 ms
1bbcb9c	1189.61 ms	1223.50 ms	33.89 ms
fd6a31c	1204.73 ms	1222.34 ms	17.61 ms
7bc3c0d	1212.35 ms	1228.94 ms	16.59 ms
5616e0a	1237.00 ms	1260.43 ms	23.43 ms
9d56232	1192.09 ms	1228.86 ms	36.77 ms
98713e6	1211.48 ms	1244.42 ms	32.94 ms
b385962	1195.85 ms	1221.63 ms	25.78 ms
4259afd	1234.04 ms	1256.76 ms	22.72 ms

App size

Revision	Plain	With Sentry	Diff
d257eb9	20.76 KiB	433.23 KiB	412.47 KiB
89bc37d	20.76 KiB	401.53 KiB	380.77 KiB
1bbcb9c	20.76 KiB	426.10 KiB	405.34 KiB
fd6a31c	20.76 KiB	436.50 KiB	415.74 KiB
7bc3c0d	20.76 KiB	427.35 KiB	406.59 KiB
5616e0a	22.85 KiB	407.45 KiB	384.60 KiB
9d56232	20.76 KiB	425.80 KiB	405.04 KiB
98713e6	20.76 KiB	435.22 KiB	414.46 KiB
b385962	20.76 KiB	399.69 KiB	378.93 KiB
4259afd	20.76 KiB	419.70 KiB	398.94 KiB

Previous results on branch: fix/tracer-crash

Startup times

Revision	Plain	With Sentry	Diff
4bfdca8	1226.92 ms	1246.14 ms	19.22 ms
b7fd8c4	1244.22 ms	1244.50 ms	0.28 ms
fc0ea36	1247.71 ms	1271.24 ms	23.53 ms
4750b1a	1256.69 ms	1278.35 ms	21.65 ms
a9d8255	1238.90 ms	1246.88 ms	7.98 ms

App size

Revision	Plain	With Sentry	Diff
4bfdca8	22.85 KiB	409.07 KiB	386.22 KiB
b7fd8c4	22.85 KiB	409.07 KiB	386.22 KiB
fc0ea36	22.85 KiB	411.38 KiB	388.53 KiB
4750b1a	22.85 KiB	409.06 KiB	386.21 KiB
a9d8255	22.85 KiB	409.07 KiB	386.22 KiB

[codecov]

Codecov Report

Merging #3333 (0aeff0a) into main (1437c68) will increase coverage by 0.053%.
The diff coverage is 94.736%.

@@              Coverage Diff              @@
##              main     #3333       +/-   ##
=============================================
+ Coverage   89.251%   89.305%   +0.053%     
=============================================
  Files          502       502               
  Lines        54400     54487       +87     
  Branches     19538     19572       +34     
=============================================
+ Hits         48553     48660      +107     
+ Misses        4986      4852      -134     
- Partials       861       975      +114     

Files	Coverage Δ
Sources/Sentry/SentryTracer.m	96.250% <100.000%> (-0.101%)	⬇️
...ts/SentryTests/Transaction/SentryTracerTests.swift	99.182% <93.750%> (-0.426%)	⬇️

... and 32 files with indirect coverage changes

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[armcknight]

Good catch. Looks basically right, I had one quick question. Ship when ready!