fix(gestures): Thread-safe SentryGestureDetector with per-gesture VelocityTracker recycle

[romtsn]

📜 Description

Three related fixes to SentryGestureDetector, the lightweight gesture detector introduced in #5138:

1. Recycle VelocityTracker per gesture. On every ACTION_UP / ACTION_CANCEL the pooled native tracker is recycled and nulled, and re-obtained lazily on the next ACTION_DOWN. Matches framework GestureDetector behavior. Previously the tracker was held for the detector's entire lifetime, keeping one pooled instance out of circulation.
2. Merge endGesture() + release() into a single recycle(). They did the same thing after the fix above.
3. Guard onTouchEvent and recycle with an AutoClosableReentrantLock. Sentry.close() is not constrained to the UI thread, so SentryWindowCallback.stopTracking() → SentryGestureDetector.recycle() can race UI-thread touch dispatch. Without synchronization that causes use-after-recycle on the native MotionEvent / VelocityTracker pools — the bg thread can return a pooled instance that UI is still calling addMovement() / computeCurrentVelocity() on, and unrelated callers that re-obtain that slot get a corrupted state. recycle() captures the native handles under the lock and performs the JNI recycle() calls outside, keeping the bg thread's critical section to a pointer swap.

SentryWindowCallback is updated for the release() → recycle() rename.

💡 Motivation and Context

Before #5138, the detector delegated to GestureDetectorCompat which didn't own pooled native resources directly, so there was no thread-safety hazard at this layer. The new lightweight detector manages MotionEvent.obtain/recycle and VelocityTracker.obtain/recycle itself, which reopens the race described above once Sentry.close() is called off the main thread.

Holding a VelocityTracker across gestures also deviates from framework behavior and unnecessarily ties up a pooled instance.

💚 How did you test it?

• Existing SentryGestureDetectorTest suite (tap / scroll / fling / cancel / multi-touch / sequential gestures) still passes.
• New test: recycle mid-gesture - subsequent gesture still fires onSingleTapUp — calls recycle() between ACTION_DOWN and a fresh gesture to verify the lazy re-obtain path and that an external mid-gesture teardown doesn't leave the detector broken.
• ./gradlew :sentry-android-core:testDebugUnitTest --tests "*SentryGestureDetectorTest*" → 11/11 pass.
• ./gradlew spotlessApply apiDump — no public API changes.

📝 Checklist

• I added GH Issue ID & Linear ID
• 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.
• I updated the wizard 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.

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

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Bug Fixes 🐛

• (gestures) Thread-safe SentryGestureDetector with per-gesture VelocityTracker recycle by romtsn in #5301

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_{🤖 This preview updates automatically when you update the PR.}

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.39.1 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	312.41 ms	356.02 ms	43.61 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d15471f	310.66 ms	368.19 ms	57.53 ms
9054d65	330.94 ms	403.24 ms	72.30 ms
b77456b	393.26 ms	441.10 ms	47.84 ms
96449e8	361.30 ms	423.39 ms	62.09 ms
ee747ae	357.79 ms	421.84 ms	64.05 ms
a416a65	295.53 ms	373.74 ms	78.21 ms
ab8a72d	316.24 ms	356.38 ms	40.14 ms
1564554	323.06 ms	336.68 ms	13.62 ms
b3d8889	371.69 ms	432.96 ms	61.26 ms
d15471f	315.20 ms	370.22 ms	55.02 ms

App size

Revision	Plain	With Sentry	Diff
d15471f	1.58 MiB	2.13 MiB	559.54 KiB
9054d65	1.58 MiB	2.29 MiB	723.38 KiB
b77456b	1.58 MiB	2.12 MiB	548.11 KiB
96449e8	1.58 MiB	2.11 MiB	539.35 KiB
ee747ae	1.58 MiB	2.10 MiB	530.95 KiB
a416a65	1.58 MiB	2.12 MiB	555.26 KiB
ab8a72d	1.58 MiB	2.12 MiB	551.55 KiB
1564554	1.58 MiB	2.20 MiB	635.33 KiB
b3d8889	1.58 MiB	2.10 MiB	535.06 KiB
d15471f	1.58 MiB	2.13 MiB	559.54 KiB