Can it detect blocking database calls?

Yes, it scans for legacy JDBC and JPA patterns like JdbcTemplate or EntityManager access which are inherently synchronous and problematic in reactive chains.

Why is blocking a problem in Spring WebFlux?

WebFlux uses a small number of event loop threads. Blocking any of these threads can lead to thread starvation, where the entire application stops responding to new requests even if CPU usage is low.

What kind of output does the skill provide?

It generates a comprehensive report categorizing findings by severity, including the file location, the specific pattern found, the context (e.g., inside a Controller), and a recommended non-blocking fix.

Does this skill support Java 21+ Virtual Threads?

Yes, it includes logic to recognize when blocking is acceptable, such as within a StructuredTaskScope or when running on a virtual thread context where blocking is much cheaper.

Spring WebFlux Performance Auditor

Name: Spring WebFlux Performance Auditor
Author: pwittchen

bypwittchen

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Analytics & Monitoring

Identifies performance-degrading blocking calls in reactive Spring WebFlux applications to prevent thread starvation and improve throughput.

About

This skill specializes in auditing Java codebases for synchronous or blocking operations that violate the reactive programming model of Spring WebFlux. It systematically searches for problematic patterns like .block() calls, blocking I/O, and thread sleeps within reactive chains, while intelligently accounting for modern Java features like Virtual Threads (Java 21+) and StructuredTaskScope. By distinguishing between safe offloading and critical event-loop blocking, it provides developers with actionable remediation steps to ensure high-performance, non-blocking service execution.

Key Features

Detects direct reactive blocking calls like .block(), .blockFirst(), and .toFuture().get()
Identifies thread-blocking operations including Thread.sleep(), synchronized blocks, and monitor waits
Flags blocking I/O and legacy JDBC/JPA calls within reactive contexts
Provides context-aware analysis for Virtual Threads and StructuredTaskScope
Generates detailed reports with severity ratings and code fix recommendations
2 GitHub stars

Use Cases

Optimizing Spring WebFlux API performance by identifying event loop bottlenecks
Modernizing legacy Java code for Java 21+ Virtual Thread environments
Auditing reactive code during PR reviews to ensure adherence to non-blocking best practices

About

Key Features

Detects direct reactive blocking calls like .block(), .blockFirst(), and .toFuture().get()
Identifies thread-blocking operations including Thread.sleep(), synchronized blocks, and monitor waits
Flags blocking I/O and legacy JDBC/JPA calls within reactive contexts
Provides context-aware analysis for Virtual Threads and StructuredTaskScope
Generates detailed reports with severity ratings and code fix recommendations
2 GitHub stars

Use Cases

Optimizing Spring WebFlux API performance by identifying event loop bottlenecks
Modernizing legacy Java code for Java 21+ Virtual Thread environments
Auditing reactive code during PR reviews to ensure adherence to non-blocking best practices