Fix missing null check when removing lifecycle observer

[markushi]

📜 Description

If Sentry.close is called off the main thread, the lifecycle watcher field is set to null, while de-registering is posted on the main thread, leading to a NPE in combination with some versions of android x lifecycle lib.

💡 Motivation and Context

Fixes #2601

💚 How did you test it?

Manual testing, the overhead of running a single test against different version of the androidx lifecycle library didn't seem to justify the efforts.

📝 Checklist

• 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	300.58 ms	357.22 ms	56.64 ms
Size	1.73 MiB	2.34 MiB	627.44 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d81684e	235.73 ms	328.76 ms	93.03 ms
17ab223	427.65 ms	484.31 ms	56.65 ms

App size

Revision	Plain	With Sentry	Diff
d81684e	1.73 MiB	2.26 MiB	547.78 KiB
17ab223	1.73 MiB	2.34 MiB	626.85 KiB

Previous results on branch: fix/npe-sentry-close-lifecycle-watcher

Startup times

Revision	Plain	With Sentry	Diff
c8d5fe8	377.53 ms	442.44 ms	64.91 ms
49c4a8c	350.21 ms	380.89 ms	30.68 ms
456e642	356.06 ms	368.73 ms	12.67 ms
f1307d7	362.40 ms	397.60 ms	35.20 ms
a7e3859	314.22 ms	378.35 ms	64.13 ms

App size

Revision	Plain	With Sentry	Diff
c8d5fe8	1.73 MiB	2.26 MiB	548.12 KiB
49c4a8c	1.73 MiB	2.34 MiB	626.94 KiB
456e642	1.73 MiB	2.26 MiB	548.12 KiB
f1307d7	1.73 MiB	2.26 MiB	548.03 KiB
a7e3859	1.73 MiB	2.26 MiB	548.12 KiB

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (6641771) 81.37% compared to head (febab27) 81.37%.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #2625   +/-   ##
=========================================
  Coverage     81.37%   81.37%           
  Complexity     4219     4219           
=========================================
  Files           337      337           
  Lines         15599    15599           
  Branches       2037     2037           
=========================================
  Hits          12693    12693           
  Misses         2111     2111           
  Partials        795      795           

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☔ View full report in Codecov by Sentry.
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[stefanosiano]

Can we also add a test to verify the change? like verifying the watcher is not null after the close function is called in a background thread and it's null only after the main thread executes?

[stefanosiano]

just a minor comment, if possible.
Looks good for everything else!

[stefanosiano]

For the main looper it should be possible to use shadowOf(Looper.getMainLooper()).idle() instead of creating a thread manually. It would be easier for readability if it works