Troubleshooting Java Deadlocks with IBM Thread and Monitor Dump Analyzer for Java Technology

How to Use IBM Thread and Monitor Dump Analyzer for Java Technology — Step‑by‑Step### Overview

IBM Thread and Monitor Dump Analyzer for Java Technology (TMDA) is a tool for analyzing Java thread dumps and monitor locks to diagnose performance problems such as deadlocks, thread contention, and thread starvation. This guide walks through preparing thread dumps, running TMDA, interpreting results, and using advanced features to troubleshoot real-world issues.

1. Preparing to Collect Thread Dumps

• Ensure you have the correct JDK/JRE and permissions to access the target Java process.
• Choose a suitable method to create thread dumps:
  • jstack (Oracle/OpenJDK): jstack -l <pid> > threaddump.txt
  • kill -3 (Unix/Linux). Send SIGQUIT to the JVM process; output usually goes to the JVM stdout/stderr file.
  • IBM Java: use jcmd, javacore, or kill -3 depending on platform and JVM version.
  • Application server utilities (WebSphere, Tomcat, etc.) often provide their own dump commands.
• Collect multiple dumps over a period (e.g., every 5–10 seconds for short-lived issues, or every few minutes for longer problems) to analyze state changes.
• Capture environment info: JVM version, heap settings, number of CPUs, application server version, recent deployments, and configuration changes.

2. Installing and Running TMDA

• Obtain TMDA: IBM provides it as part of diagnostic tools or separate downloads for certain platforms. Ensure you have the version compatible with your JVM and OS.
• TMDA typically runs as a GUI application but also offers command-line options.
• Launch the tool and open a thread dump file (javacore, threaddump.txt, or similar). You can also feed multiple dumps for time-series analysis.

Command-line example (if available):

java -jar tmda.jar -input threaddump.txt -output report.html 

3. Basic TMDA Workflow

1. Open the thread dump file(s) in TMDA.
2. Let TMDA parse the file; it will identify deadlocks, blocked threads, waiting threads, and threads in runnable state.
3. Examine the summary/dashboard that lists:
   • Number of threads
   • Detected deadlocks
   • Top locks causing blocking
   • Threads consuming CPU (if CPU profiling info present)
4. Navigate to specific threads of interest and inspect stack traces and monitor/lock ownership.

4. Interpreting Key Findings

• Deadlocks: TMDA will show the exact threads and monitors involved in a deadlock cycle. The crucial action is to identify the code paths where locks are acquired out of order and refactor to avoid circular waits.
  • Action: Reorder lock acquisition, use timed lock attempts (tryLock), or reduce lock granularity.
• Blocked threads: Threads waiting to acquire a monitor owned by another thread.
  • Action: Identify the owner thread’s stack to see why it isn’t releasing the lock — long-running I/O, synchronized methods, or nested locks.
• Waiting threads: Typically waiting on Object.wait(), Thread.join(), or Condition.await().
  • Action: Verify proper notify/notifyAll usage and check for missed signals or incorrect condition predicates.
• High runnable threads: Many RUNNABLE threads on fewer CPUs may indicate CPU contention or busy-wait loops.
  • Action: Profile CPU hotspots, check for tight loops, and consider throttling or batching work.
• Native or JNI issues: Threads stuck in native methods could point to native library problems or blocking I/O.

5. Example Walkthrough

Scenario: Web application experiencing high latency and sporadic request stalls.

1. Collect three thread dumps spaced 5 seconds apart.
2. Load dumps into TMDA and review the summary.
3. TMDA reports multiple threads blocked on monitor com.example.Cache with owner thread “CacheCleaner”.
4. Inspect “CacheCleaner” stack: it holds the lock while performing a long network call to refresh entries.
5. Resolution: Change cache refresh to use a separate lock or perform the network call outside synchronized sections; implement read-write locks or ConcurrentHashMap to reduce contention.

6. Advanced Tips

• Use the time-series feature (compare multiple dumps) to see lock ownership changes and thread state transitions.
• Integrate with CPU profilers (e.g., IBM Health Center, async-profiler) for combined CPU and thread analysis.
• Map thread names to application components — include meaningful thread naming in your code (ThreadFactory).
• For WebSphere or IBM JVMs, correlate TMDA findings with javacore, heapdump, and system dumps for deeper investigation.
• Save reports and annotate findings to build a knowledge base for recurring issues.

7. Common Pitfalls

• Single dump limitations: A single snapshot can miss transient conditions; always prefer multiple dumps.
• Misinterpreting WAITING vs BLOCKED: WAITING often means waiting for a condition—check wait/notify logic. BLOCKED means waiting for a monitor.
• Ignoring thread naming: Anonymous thread names make diagnosis harder—adopt descriptive names in application code.

8. Quick Reference Commands

• Capture thread dump with jstack:

  
  jstack -l <pid> > threaddump.txt 

• Send SIGQUIT (Unix):

  
  kill -3 <pid> 

9. Conclusion

TMDA is a powerful tool for diagnosing Java threading problems when used with good dump-collection practices and an understanding of lock/monitor semantics. Focus on collecting multiple, well-timed dumps, interpret TMDA’s deadlock and blocking reports, and apply code-level fixes such as reducing lock scope, using non-blocking data structures, or reworking long-running synchronized sections.