Make seeder thread pool sizes configurable (fixes #1429)

[petersmythe]

Summary

Makes the GeoWebCache seeder thread pool sizes configurable via geowebcache.xml (primary configuration) with environment variable overrides for Docker/cloud deployments, as requested in #1429.

Previously, the core pool size (16) and max pool size (32) were hardcoded in Spring XML with no way to override them without modifying the application context.

Configuration

Primary: geowebcache.xml

<gwcConfiguration>
  ...
  <seederCorePoolSize>24</seederCorePoolSize>
  <seederMaxPoolSize>64</seederMaxPoolSize>
  ...
</gwcConfiguration>

Element	Description	Default
seederCorePoolSize	Core thread pool size for seeding tasks	16
seederMaxPoolSize	Maximum thread pool size for seeding tasks	32

Override: Environment variables

For Docker/cloud deployments, the XML configuration can be overridden:

Override	Overrides
GWC_SEEDER_CORE_POOL_SIZE	seederCorePoolSize
GWC_SEEDER_MAX_POOL_SIZE	seederMaxPoolSize

Precedence: Environment variable / system property (-D) → geowebcache.xml → hardcoded default (16/32).

Changes

• ServerConfiguration: Added getSeederCorePoolSize() / getSeederMaxPoolSize() default interface methods.
• GeoWebCacheConfiguration: Added seederCorePoolSize / seederMaxPoolSize fields (POJO for geowebcache.xml).
• geowebcache.xsd: Added <seederCorePoolSize> and <seederMaxPoolSize> schema elements.
• geowebcache.xml (example): Added commented-out example.
• geowebcache-core-context.xml: Bean wiring now reads from gwcXmlConfig via SpEL, falling back to 16/32.
• SeederThreadPoolExecutor: Added resolvePoolSize() for env var override with validation (invalid values fall back to defaults, core > max auto-adjusts).
• New SeederThreadPoolExecutorTest with 9 test cases.
• Documentation updated in production/index.rst.

Backward Compatibility

• The Spring XML bean definitions now read from the configuration object but fall back to 16/32 if not set — existing deployments without seederCorePoolSize/seederMaxPoolSize in their geowebcache.xml continue to work unchanged.
• SeederThreadLocalTransferExecutor (GeoServer subclass) works without modification.
• No changes to the constructor signature.

Testing

• 9 unit tests covering: defaults, system property override, partial override, invalid values (non-numeric, negative, zero), whitespace handling, trimming, and corePoolSize > maxPoolSize adjustment.
• Manually tested in Docker with GeoServer 3.0.x nightly — confirmed 24 threads active matching GWC_SEEDER_CORE_POOL_SIZE=24 via jcmd Thread.print.

Supersedes

This replaces the approach in #1430 which used Spring property placeholders in the XML. That approach had test failures and didn't meet the requirement of being configurable outside of application contexts.

Closes #1429

[Copilot]

Pull request overview

Makes the GeoWebCache seeder thread pool core/max sizes configurable at the Java level (system property → env var → constructor default), so they can be overridden without editing Spring XML. The constructor signature is unchanged, preserving backward compatibility with SeederThreadLocalTransferExecutor and existing wirings.

Changes:

• Add GWC_SEEDER_CORE_POOL_SIZE / GWC_SEEDER_MAX_POOL_SIZE constants and a resolvePoolSize helper in SeederThreadPoolExecutor, with auto-adjustment when core > max and a startup info log of the effective sizes.
• New SeederThreadPoolExecutorTest covering defaults, overrides, invalid/blank/negative values, whitespace trimming, and core-exceeds-max adjustment, using the existing PropertyRule test rule.
• Documentation section added under production/index.rst describing the new properties, precedence, and the auto-adjust behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
geowebcache/core/src/main/java/org/geowebcache/seed/SeederThreadPoolExecutor.java	Adds runtime resolution of core/max pool sizes from system properties/env vars with fallback to constructor defaults.
geowebcache/core/src/test/java/org/geowebcache/seed/SeederThreadPoolExecutorTest.java	New unit tests exercising default, override, invalid, and core>max scenarios via PropertyRule.
documentation/en/user/source/production/index.rst	Documents the new configuration properties, precedence, and adjustment behavior.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[aaime]

GeoWebCache has a configuration file, it's geowebcache.xml, new configurations should go in there... an env variable override makes some sense too, but as an override, not straight configuration. Most of the GWC configuration is in that XML file, we should not create a parallel configuration system just because it's convenient to code.

[petersmythe]

GeoWebCache has a configuration file, it's geowebcache.xml, new configurations should go in there... an env variable override makes some sense too, but as an override, not straight configuration. Most of the GWC configuration is in that XML file, we should not create a parallel configuration system just because it's convenient to code.

Thank you, of course it should. I will rework.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

[petersmythe]

Ready and tested again. Thanks for the feedback.