perf(core): Skip Hint allocation in addBreadcrumb without callback

[runningcode]

Resolves JAVA-605.

Description

Scope.addBreadcrumb(Breadcrumb, Hint) allocated a Hint unconditionally when the caller passed null, even though the Hint is only ever used to pass to the beforeBreadcrumb callback. When no callback is configured (the common case) the Hint — a HashMap + ArrayList + AutoClosableReentrantLock — was created and immediately discarded on every breadcrumb.

This moves the allocation inside the callback != null branch, so no Hint is allocated on the common path.

Pure allocation elimination, no behavior change.

Source

Found via on-device Perfetto method-trace analysis of the Android SDK (Scope#addBreadcrumb breadcrumb path). Part of Reduce SDK init time [Android].

🤖 Generated with Claude Code

Benchmark

Measured on-device with androidx Microbenchmark 1.4.1 (benchmark-junit4) on a Samsung Galaxy A55 (SM-A556B), Android API 36 (release build, non-minified).

The benchmark exercises the caller-side cost of a scope mutation with scope persistence enabled (enableScopePersistence = true, cacheDirPath set, no beforeBreadcrumb). The async serialize + disk write is dispatched to a no-op executor so it never runs on the measured thread — mirroring production, where it runs off-thread. Each branch is compared against its base commit (aab952b82e); the per-branch delta isolates this change. allocationCount is deterministic; timeNs has ~±10 ns run-to-run noise on a non-rooted device (unlocked clocks), so it is reported as a median and reproduced across 2 runs.

How it was done

A local, uncommitted androidx microbenchmark module (sentry-android-integration-tests/sentry-uitest-android-microbenchmark) depending on :sentry, with a BenchmarkRule looping the scope mutation. Run with:

./gradlew :sentry-android-integration-tests:sentry-uitest-android-microbenchmark:connectedReleaseAndroidTest \
  -Pandroid.testInstrumentationRunnerArguments.androidx.benchmark.suppressErrors=UNLOCKED

Result — scope.addBreadcrumb()

Metric	main	This PR	Delta
allocationCount	7	3	-4 per breadcrumb
timeNs (median)	~242 ns	185 ns	~-24%

The 4 eliminated allocations are the Hint plus its HashMap, ArrayList, and AutoClosableReentrantLock. The setTag control path (unaffected by this change) was unchanged at ~127 ns / 3 allocs.

[linear-code]

JAVA-605

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.47.0 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	362.05 ms	419.80 ms	57.75 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
3d205d0	352.15 ms	432.53 ms	80.38 ms
e59e22a	368.02 ms	432.00 ms	63.98 ms
806307f	357.85 ms	424.64 ms	66.79 ms
d364ace	384.53 ms	453.51 ms	68.98 ms
4c04bb8	307.93 ms	362.34 ms	54.41 ms
bb0ff41	312.86 ms	363.78 ms	50.92 ms
91bb874	310.68 ms	359.24 ms	48.56 ms
11f90db	314.26 ms	372.43 ms	58.17 ms
f6cdbf0	314.19 ms	357.59 ms	43.40 ms
8687935	332.52 ms	362.23 ms	29.71 ms

App size

Revision	Plain	With Sentry	Diff
3d205d0	1.58 MiB	2.10 MiB	532.97 KiB
e59e22a	1.58 MiB	2.20 MiB	635.34 KiB
806307f	1.58 MiB	2.10 MiB	533.42 KiB
d364ace	1.58 MiB	2.11 MiB	539.75 KiB
4c04bb8	0 B	0 B	0 B
bb0ff41	0 B	0 B	0 B
91bb874	1.58 MiB	2.13 MiB	559.07 KiB
11f90db	0 B	0 B	0 B
f6cdbf0	0 B	0 B	0 B
8687935	1.58 MiB	2.19 MiB	619.17 KiB

Previous results on branch: no/java-605-avoid-hint-allocation

Startup times

Revision	Plain	With Sentry	Diff
f1645b1	354.71 ms	435.38 ms	80.67 ms

App size

Revision	Plain	With Sentry	Diff
f1645b1	0 B	0 B	0 B