blockless-spring-grpc-example

A Spring Boot + gRPC demo app showing blockless in action.

What it demonstrates

RPC	Blockless feature	What it proves
Greet	Blockless.get()	Wait on a slow downstream without blocking platform threads
GreetAll	Parallel.map() + withMaxConcurrency(5)	Bounded parallel fan-out with gRPC + MDC context propagation
GreetSafe	Parallel.toEither()	Partial failure handling — some succeed, some fail, results stay in order

Context propagation: SLF4J MDC traceId and gRPC Context flow from the incoming request through virtual threads via Slf4jMdcContextPropagator and GrpcContextPropagator.

Run

mvn spring-boot:run

gRPC server starts on port 9090.

Try it

Requires grpcurl.

Single greeting — Blockless.get():

grpcurl -plaintext -d '{"name": "Toothless"}' localhost:9090 org.pjlabs.example.GreetingService/Greet

Fan-out — Parallel.map() with bounded concurrency:

grpcurl -plaintext -d '{"names": ["Alpha", "Beta", "Gamma", "Delta", "Epsilon"]}' localhost:9090 org.pjlabs.example.GreetingService/GreetAll

Partial failure — Parallel.toEither(), pass "FAIL" to trigger an error:

grpcurl -plaintext -d '{"names": ["Alpha", "FAIL", "Gamma"]}' localhost:9090 org.pjlabs.example.GreetingService/GreetSafe

With trace-id — context propagation through virtual threads:

grpcurl -plaintext -H 'trace-id: dragon-trace-789' -d '{"names": ["A", "B", "C"]}' localhost:9090 org.pjlabs.example.GreetingService/GreetAll

Check the app logs to see thread names, virtual thread info, and traceId flowing through.

Tests

mvn test

8 tests covering:

• Blockless.get() round-trip
• Parallel.map() fan-out correctness and parallelism (5 x 100ms in <400ms)
• Parallel.toEither() partial failure and all-success cases
• MDC traceId propagation from gRPC header to each virtual thread

Requirements

• Java 21+
• Maven

License

Apache 2.0