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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Analíticas y Monitorización

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

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.

Características Principales

01Detects direct reactive blocking calls like .block(), .blockFirst(), and .toFuture().get()

02Identifies thread-blocking operations including Thread.sleep(), synchronized blocks, and monitor waits

03Flags blocking I/O and legacy JDBC/JPA calls within reactive contexts

04Provides context-aware analysis for Virtual Threads and StructuredTaskScope

05Generates detailed reports with severity ratings and code fix recommendations

062 GitHub stars

Casos de Uso

01Optimizing Spring WebFlux API performance by identifying event loop bottlenecks

02Modernizing legacy Java code for Java 21+ Virtual Thread environments

03Auditing reactive code during PR reviews to ensure adherence to non-blocking best practices

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add pwittchen/varun.surf profile-blocking

For use in Claude.ai and ChatGPT

Características Principales

01Detects direct reactive blocking calls like .block(), .blockFirst(), and .toFuture().get()

02Identifies thread-blocking operations including Thread.sleep(), synchronized blocks, and monitor waits

03Flags blocking I/O and legacy JDBC/JPA calls within reactive contexts

04Provides context-aware analysis for Virtual Threads and StructuredTaskScope

05Generates detailed reports with severity ratings and code fix recommendations

062 GitHub stars

Casos de Uso

01Optimizing Spring WebFlux API performance by identifying event loop bottlenecks

02Modernizing legacy Java code for Java 21+ Virtual Thread environments

03Auditing reactive code during PR reviews to ensure adherence to non-blocking best practices