AgentSkillsCN

jstack

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SKILL.md

You are analyzing a Java thread dump to identify deadlocks, performance issues, and thread contention.

Step 1: Capture the thread dump

If the user provided a file path, skip to Step 2.

If no file path was provided, help capture a thread dump from a running Gradle worker JVM:

  1. •

    Find Gradle worker processes:

    bash
    jps -l | grep GradleWorkerMain
  2. •

    If multiple workers are found, ask the user which PID to analyze (or analyze all if requested)

  3. •

    Capture the thread dump:

    bash
    jstack <PID> > /tmp/jstack-<PID>.txt
  4. •

    Proceed to analyze the captured dump file

Step 2: Analyze the thread dump

Launch a general-purpose Task subagent with the following instructions:

Read and analyze the jstack thread dump at: {{arg1}} (or the file path from Step 1)

Your analysis should identify:

  1. •Deadlocks - Any threads waiting on locks held by each other (jstack usually reports these at the top)
  2. •Blocked threads - Threads in BLOCKED state and what locks they're waiting for
  3. •Lock contention - Locks (monitors) with multiple threads waiting on them
  4. •Thread states distribution - Count of RUNNABLE, WAITING, TIMED_WAITING, BLOCKED threads
  5. •Thread pool health - Look for exhausted thread pools (e.g., all threads in pool are blocked/waiting)
  6. •Suspicious patterns - Threads stuck in the same operation, recursive locks, etc.
  7. •Hot code paths - Stack traces that appear frequently across threads

Provide:

  • •Executive Summary - Critical issues found (deadlocks, severe contention, etc.)
  • •Deadlock Analysis - Full details of any deadlock cycles with thread names, IDs, and lock objects
  • •Thread Contention - Locks with high contention (multiple waiters) and what threads hold them
  • •Thread State Overview - Statistics on thread states
  • •Problematic Threads - Details on blocked/waiting threads with context
  • •Code Locations - If identifiable, map issues to code locations in the codebase
  • •Recommended Actions - Specific steps to resolve the issues

Format your response in clear markdown with sections for each category. Include relevant thread IDs, lock addresses, and stack trace excerpts to support findings.