jstack

About

jstack is a JDK utility used to generate thread dumps of a Java process. A thread dump contains a snapshot of all the threads running in the Java Virtual Machine (JVM) at a given time. It is useful for diagnosing issues like deadlocks, high CPU usage, thread contention, or long-running threads.

Key Use Cases

• Identifying thread contention and deadlocks.

• Debugging threads stuck in infinite loops or blocking states.

• Understanding CPU-bound threads or hung processes.

Steps to Use jstack on Mac

1. Find the Process ID (PID):

• Open the terminal and use the jps command to list all Java processes:

jps

Output example:

Start the Java Application (here it is sample-print-service maven springboot application)

jps command output is below

Here, 83322 is the PID of our Springboot app.

2. Generate a Thread Dump:

• Run the jstack command with the PID to generate a thread dump:

jstack 83322 > thread-dump.txt

This saves the thread dump to a file named thread-dump.txt in the current directory.

27KB

thread-dump.txt

3. Analyze the Thread Dump:

• Open the thread-dump.txt file and look for:

  • BLOCKED or WAITING states indicating thread contention.

  • Deadlock information, which is explicitly mentioned if detected.

  • Long-running threads consuming resources.