perf: Share one executor between log and metrics batch processors (JAVA-653)

[runningcode]

📜 Description

LoggerBatchProcessor and MetricsBatchProcessor each constructed their own SentryExecutorService, so an app with both logs and metrics enabled ran two dedicated threads for structurally identical work (a 5-second flush loop that batches events and hands them to the transport).

SentryClient now owns a single SentryExecutorService, created only when logs or metrics are enabled, and exposes it via getBatchProcessorExecutorService(). The default factories inject it into both processors (through the existing 3-arg LoggerBatchProcessor constructor and a new matching one on MetricsBatchProcessor). The pluggable factory interfaces are unchanged.

The shutdown paths already close the executor from each processor's close(); since the executor is now shared, the second close is a safe no-op, and the restart branch's submit(...) is guarded with the same RejectedExecutionException fallback already used in Scopes.close() for the main executor.

💡 Motivation and Context

Part of reducing the number of threads created by the SDK: JAVA-653.

Saves one thread for every app that has both logs and metrics enabled. The executor is created only when at least one of logs or metrics is enabled, and its worker thread is spawned only when the first flush is scheduled.

Note for reviewers

Custom ILoggerBatchProcessorFactory / IMetricsBatchProcessorFactory implementations that call the public 2-arg processor constructors still get an independent executor (unchanged behavior). Only the default factories opt into the shared one.

💚 How did you test it?

New SentryClientTest case asserting both processors receive the same executor instance (and that it is the client's shared one), plus the existing LoggerBatchProcessorTest, MetricsBatchProcessorTest, SentryClientTest, LoggerApiTest, and MetricsApiTest suites.

📝 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

Related PRs in this effort: RateLimiter (#5814), LifecycleWatcher (#5819), performance collector (#5816), HostnameCache (#5817).

🤖 Generated with Claude Code

[linear-code]

JAVA-653

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.50.0 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	427.22 ms	526.69 ms	99.48 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
eb95ded	317.51 ms	369.08 ms	51.57 ms
2124a46	319.19 ms	415.04 ms	95.85 ms
c3ee041	310.64 ms	361.90 ms	51.26 ms
dcc6bbf	382.58 ms	462.13 ms	79.54 ms
7a19fee	315.46 ms	368.62 ms	53.16 ms
9054d65	330.94 ms	403.24 ms	72.30 ms
d500866	326.13 ms	378.70 ms	52.58 ms
ad8da22	365.86 ms	427.00 ms	61.14 ms
ed33deb	337.52 ms	484.06 ms	146.54 ms
d15471f	310.26 ms	377.04 ms	66.78 ms

App size

Revision	Plain	With Sentry	Diff
eb95ded	0 B	0 B	0 B
2124a46	1.58 MiB	2.12 MiB	551.51 KiB
c3ee041	0 B	0 B	0 B
dcc6bbf	1.58 MiB	2.12 MiB	553.10 KiB
7a19fee	0 B	0 B	0 B
9054d65	1.58 MiB	2.29 MiB	723.38 KiB
d500866	0 B	0 B	0 B
ad8da22	1.58 MiB	2.29 MiB	719.83 KiB
ed33deb	1.58 MiB	2.13 MiB	559.52 KiB
d15471f	1.58 MiB	2.13 MiB	559.54 KiB