Add optional executor to GrpcPlatformServerDefinition

[RishabhB99]

Problem

GrpcPlatformServiceContainer.initializeBuilder(...) builds the network gRPC server but never calls ServerBuilder.executor(...). As a result gRPC falls back to its default unbounded cached thread pool to run RPC handlers.

For services whose handlers block (e.g. making downstream I/O calls to other services), this means one platform thread is pinned per concurrent in-flight RPC, with no ceiling. Under load this leads to unbounded thread growth and eventually OutOfMemoryError: unable to create native thread. There is currently no config key, builder field, or overridable hook for a subclass to supply its own server executor.

Change

Expose an optional Executor on GrpcPlatformServerDefinition and wire it into the NettyServerBuilder when present:

if (serverDefinition.getExecutor() != null) {
  builder.executor(serverDefinition.getExecutor());
}

• Fully backward compatible: when the field is null (the default), no .executor(...) call is made and behavior is identical to today (gRPC's default executor).
• The framework itself takes no new dependency and stays JDK-agnostic — it merely accepts an Executor. The caller chooses the implementation.

Motivation / usage

Services on JDK 21 can now supply Executors.newVirtualThreadPerTaskExecutor() so that blocking handler work no longer pins platform threads (virtual threads unmount during I/O), decoupling live thread count from request concurrency. Services that prefer explicit back-pressure can instead supply a bounded ThreadPoolExecutor.

Example (subclass overriding getServerDefinitions()):

GrpcPlatformServerDefinition.builder()
    .name(getServiceName())
    .port(getServicePort())
    .serviceFactory(...)
    .executor(Executors.newVirtualThreadPerTaskExecutor())
    .build();

Testing

./gradlew :platform-grpc-service-framework:compileJava :platform-grpc-service-framework:spotlessJavaCheck passes. This module has no existing test source set, and initializeBuilder is private; given the change is a backward-compatible optional pass-through to NettyServerBuilder.executor(...), no test harness was scaffolded. Happy to add one if maintainers prefer.

🤖 Generated with Claude Code