reactor/BlockHound

Health v2 · maintenance only

Adoption not part of the score

1507 stars · 95 forks observed · 2026-09-26

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

BlockHound is a Java agent that detects blocking calls (like IO or Thread.sleep) made from threads marked as non-blocking, such as Reactor's parallel scheduler threads. It transparently instruments JVM classes and throws an error pinpointing the exact location of the offending blocking call.

Use cases

• detect blocking calls in reactive code
• find Thread.sleep in non-blocking threads
• debug Project Reactor applications for blocking operations
• catch accidental blocking IO in event loop threads
• verify non-blocking guarantees in tests
• locate source of BlockingOperationError in reactive pipelines

When to choose

• you develop reactive applications with Project Reactor or RxJava
• you want to enforce non-blocking discipline in tests
• you need to pinpoint exactly where blocking calls happen in async code

When to avoid

• your codebase is purely blocking/synchronous
• you need runtime production monitoring rather than detection during development or testing
• you work outside the JVM ecosystem

Facets

library · maturity stable

testing developer-tools developer-tools testing performance jvm cross-platform java-agent reactor reactive-programming non-blocking blocking-detection bytecode-instrumentation instrumentation

Member repositories

For agents

markdown · JSON · MCP: product_card(name="reactor/BlockHound")