Identifying threads that are consuming a high amount of CPU from a thread dump can be a bit tricky because thread dumps alone do not show CPU usage directly. They give a snapshot of what each thread is doing at the moment the dump was taken. However, you can use thread dumps in conjunction with other tools to diagnose high CPU usage issues. Here’s how you can approach it:
1. Collect Thread Dumps Repeatedly: Take several thread dumps a few seconds apart. Threads that appear to be running in each dump (and occupying similar stack traces) are likely consuming CPU resources.
2. Use Operating System Tools: Tools like top on Linux/Unix or Task Manager on Windows can help you see which processes are using the most CPU. If you’re using a Unix-like system, you can use the top -H command to view CPU usage by threads within processes.
3. Correlate with PID or TID: Once you identify high CPU threads via system tools, correlate these with your Java threads.
• On Linux, you can use ps -Lfp <pid> to list all threads of a Java process. Note down the LWP (Light Weight Process) or TID (Thread ID) of the high CPU threads.
• You can find this TID in your Java thread dumps prefixed by nid (Native ID) which you match with the LWP/TID from your system tools.
4. Analyze Java Thread Stacks: Once you’ve identified the threads of interest in the thread dumps by their nid, analyze their stack traces. Look for:
• Long-running loops
• Intensive calculations
• Blocking operations (e.g., network or I/O operations that might be taking a long time due to external factors)
5. JVM Profiling Tools: Use JVM profiling tools such as JProfiler, VisualVM, or YourKit. These tools can provide a real-time breakdown of CPU usage by threads and help identify the methods that are consuming the most CPU.
6. Logging and Monitoring: Implement logging in your application to track performance and CPU usage metrics. Monitoring tools like New Relic, Datadog, or Prometheus can provide insights over time and help correlate issues with changes in the environment or codebase.
By following these steps, you can better understand which threads are using high CPU and investigate the reasons behind their behavior.