perf(core): Drop per-instance lock from SentryId and SpanId

[runningcode]

📜 Description

SentryId and SpanId stored their string value behind a LazyEvaluator<String>. Each LazyEvaluator allocates an AutoClosableReentrantLock (a ReentrantLock subclass, including its internal Sync object) plus a capturing lambda — on every instance.

This change replaces the LazyEvaluator<String> in both classes with a plain volatile String guarded by a double-checked synchronized (this) block:

• Eager (string-arg) constructors now assign the value directly — no lazy wrapper, no lock.
• The no-arg / UUID constructors still defer UUID-string generation; SentryId keeps the UUID reference so toSentryIdString stays lazy.
• Synchronization is retained (not a lock-free race) because UUID generation is non-idempotent — two racing threads must not produce different ids for the same instance.

No public API change (apiDump produces no diff).

💡 Motivation and Context

One SentryId is created per event/transaction and one SpanId per span, so these are among the most frequently allocated objects in the SDK. Paying for a per-instance ReentrantLock + lambda to guard a single String is pure overhead, and the eager string-arg constructors got no laziness benefit at all. Follow-up to the SDK Overhead Reduction work (#5499).

Resolves JAVA-589.

💚 How did you test it?

Existing SpanIdTest and SentryIdTest cover the lazy-generation and normalization behavior (UUID generated/normalized only once, not on init, etc.). The full :sentry unit test suite passes (3372/3373; the one failing SentryIdTest case is a pre-existing test-isolation artifact that fails identically on main and is unrelated to this change).

Benchmark

Measured against main using the real compiled classes on the same JVM (Temurin 17.0.16). Allocation is measured via ThreadMXBean.getThreadAllocatedBytes (exact TLAB accounting), with objects stored into a live array so the JIT can't scalar-replace them. Throughput is single-threaded, best-of-10 measured rounds after 5 warmup rounds of 1M ops each.

Scenario	Bytes/op (before → after)	Δ bytes	Throughput ops/ms (before → after)	Speedup
SpanId(String) eager	104 → 16	−88 (−85%)	93,580 → 458,935	4.9×
SpanId() lazy + toString	232 → 144	−88 (−38%)	41,587 → 65,556	1.6×
SentryId(String) eager	104 → 24	−80 (−77%)	138,296 → 312,029	2.3×
SentryId() lazy + toString	320 → 208	−112 (−35%)	26,472 → 34,084	1.3×
SentryId(UUID) lazy + toString	408 → 304	−104 (−25%)	4,430 → 4,579	1.03×

The ~88-byte reduction on eager SpanId accounts exactly for the removed object graph: LazyEvaluator (24B) + AutoClosableReentrantLock (16B) + its internal NonfairSync/AQS (32B) + the capturing lambda (16B). Eager constructors (hot deserialization/propagation paths) win biggest. The lazy paths still shed the lock machinery; SentryId(UUID) throughput barely moves because that path is dominated by UUID.randomUUID() (a SecureRandom draw), not the lock.

📝 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

Other LazyEvaluator/AutoClosableReentrantLock usages that guard genuinely light objects can be reviewed similarly as part of the SDK overhead reduction effort.

[linear-code]

JAVA-589

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.46.0 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	317.23 ms	362.98 ms	45.75 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