perf(core): Lazily allocate AutoClosableReentrantLock (JAVA-588)

[runningcode]

📜 Description

io.sentry.util.AutoClosableReentrantLock extended java.util.concurrent.locks.ReentrantLock, and ~57 SDK classes create one eagerly in a field initializer. Constructing the SDK object graph therefore allocated a ReentrantLock (plus its AbstractQueuedSynchronizer Sync) per object — even for objects whose lock is never acquired.

This change holds the ReentrantLock internally and creates it lazily on the first acquire(), using an AtomicReferenceFieldUpdater CAS so the lazy creation is atomic and stays Loom-friendly (no synchronized, preserving the intent of #3715). The lifecycle token captures the resolved lock instance so close() unlocks the correct one.

💡 Motivation and Context

Part of the Reduce SDK init time [Android] effort (JAVA-588). A customer-provided Perfetto trace showed ~81 ReentrantLock allocations on the main thread under SentryAndroid.init, contributing GC pressure and main-thread CPU. With lazy allocation, only locks actually acquired during init allocate; the many never-contended locks no longer allocate at construction.

Compatibility note: this is technically a binary-compatibility change — AutoClosableReentrantLock no longer extends ReentrantLock, so the inherited ReentrantLock public methods leave its API surface (reflected in sentry.api). A usage audit confirmed every call site uses only acquire() (try-with-resources); nothing calls lock()/unlock()/tryLock()/isHeldByCurrentThread() directly or types a field/param as ReentrantLock, so no caller is affected.

A new on-device A/B benchmark (LockAllocationBenchmarkTest, not run in CI) quantifies the allocation reduction and confirms acquire() hot-path throughput is unchanged.

💚 How did you test it?

Unit tests in AutoClosableReentrantLockTest (lazy creation, reentrancy, and an 8-thread × 1000-iteration mutual-exclusion stress test); full :sentry:test suite green.

📝 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.

🔮 Next steps

Biggest remaining main-thread init cost in the same trace is Manifest parsing (~147ms) — tracked separately (SDK-1322 / JAVA-531, compile-time injection).

Fixes JAVA-588

[linear-code]

JAVA-588

[github-actions]

	Fails
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## Unreleased

### Performance

- Lazily allocate AutoClosableReentrantLock (JAVA-588) ([#5643](https://github.com/getsentry/sentry-java/pull/5643))

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Generated by 🚫 dangerJS against 510e290

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.45.0 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	330.67 ms	380.76 ms	50.09 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
18c0bc2	306.73 ms	349.77 ms	43.03 ms
0eaac1e	316.82 ms	357.34 ms	40.52 ms
d15471f	303.49 ms	439.08 ms	135.59 ms
fc5ccaf	276.52 ms	370.46 ms	93.93 ms
e2dce0b	308.96 ms	360.10 ms	51.14 ms
5b1a06b	352.27 ms	413.70 ms	61.43 ms
37ec571	366.04 ms	424.28 ms	58.23 ms
9fbb112	361.43 ms	427.57 ms	66.14 ms
bbc35bb	324.88 ms	425.73 ms	100.85 ms
ff8eea4	313.42 ms	337.08 ms	23.66 ms

App size

Revision	Plain	With Sentry	Diff
18c0bc2	1.58 MiB	2.13 MiB	557.33 KiB
0eaac1e	1.58 MiB	2.19 MiB	619.17 KiB
d15471f	1.58 MiB	2.13 MiB	559.54 KiB
fc5ccaf	1.58 MiB	2.13 MiB	557.54 KiB
e2dce0b	0 B	0 B	0 B
5b1a06b	0 B	0 B	0 B
37ec571	0 B	0 B	0 B
9fbb112	1.58 MiB	2.11 MiB	539.18 KiB
bbc35bb	1.58 MiB	2.12 MiB	553.01 KiB
ff8eea4	1.58 MiB	2.28 MiB	718.64 KiB