How does this skill simplify the process of debugging Java application hangs?

This skill automates the identification of thread-locking issues like circular deadlocks, lock convoys, and connection pool starvation by analyzing live thread dumps and JFR data, eliminating the need for manual, error-prone parsing of raw JVM logs.

What are the specific technical requirements for running this skill?

The skill requires a host running JDK 8u262 or JDK 11+ and functions on any system where the javaperf MCP server is installed with local attach permissions for the target JVM.

Can this skill diagnose intermittent performance issues, or only total system freezes?

While standard thread dumps identify current deadlocks, the JFR profiling feature captures transient lock contention and wait durations over time, allowing the agent to diagnose intermittent performance dips that don't result in a total freeze.

Does this work with common Java frameworks like Spring Boot or Tomcat?

Yes, this skill is specifically designed to recognize thread patterns in popular frameworks like Tomcat, HikariCP, and ForkJoinPool, making it highly effective for identifying infrastructure-level bottlenecks.

What exactly is included in the purchase of this skill?

Upon purchase, you receive the production-ready skill definition, including all necessary tool mappings for thread analysis and JFR profiling, along with documentation for integrating it into your MCP-compatible AI agent environment.

javaperf threads deadlocks

I have analyzed the thread state for PID 4521. The investigation detected a classic deadlock between two worker threads and evidence of starvation in the HTTP NIO pool.

JVM Thread Analysis Report (PID 4521)

Thread Name	State	Lock Identifier	Lock Owner	Stack Frame (Top)
`inventory-svc-1`	BLOCKED	`0x000000071234 (OrderSync)`	`inventory-svc-2`	`com.app.Inv.update(Inv.java:42)`
`inventory-svc-2`	BLOCKED	`0x000000075678 (StockSync)`	`inventory-svc-1`	`com.app.Stock.reserve(Stock.java:88)`
`http-nio-8080-1`	WAITING	`0x000000079999 (HikariPool)`	N/A	`com.zaxxer.hikari.pool.HikariPool.getConnection`
`http-nio-8080-2`	WAITING	`0x000000079999 (HikariPool)`	N/A	`com.zaxxer.hikari.pool.HikariPool.getConnection`

Hot Locks (JFR Data)

Lock / Class	Total Wait Time	Wait Count	Top Waiting Stack
`java.util.concurrent.locks.ReentrantLock$NonfairSync`	45,201 ms	12	`com.app.service.SharedService.process`
`com.zaxxer.hikari.pool.ProxyConnection`	12,400 ms	85	`com.app.dao.BaseDao.query`

Verdict: Deadlock detected between inventory worker threads. Secondary pool starvation observed in the HTTP NIO pool due to threads waiting indefinitely for DB connections that are never released by the deadlocked threads.

Fix to try:

Implement a consistent locking order for OrderSync and StockSync resources to break the cycle.
Add a connection-timeout to the HikariCP configuration to prevent the entire HTTP pool from hanging.
Wrap the synchronized blocks in tryLock with a timeout to allow graceful failure.

Next steps

Apply the lock ordering fix to the Inventory and Stock classes.
Restart the JVM and run check_deadlock to verify the cycle is resolved.
Monitor profile_jfr_locks for 5 minutes to ensure no new contention points emerge.

About this skill

Diagnoses hung or stuck Java apps, deadlocks, lock contention, and thread pool starvation using live thread dumps, deadlock detection, and JFR lock events via the javaperf MCP server. Use when the user says the Java app hangs, freezes, stops responding, requests pile up or time out with low CPU, suspects a deadlock, or asks why threads are BLOCKED or WAITING.

Frequently Asked Questions

javaperf threads deadlocks