Which method is the least obtrusive for generating thread dumps in java?

Question

I am aware of the following methods for generating thread dumps in java:

• kill -3
• jstack
• JMX from inside the JVM
• JMX remote
• JPDA (remote)
• JVMTI (C API)

Of these methods, which is the least detrimental to the JVM's performance?

Answer 1

If you just need to dump all stack traces to stdout, kill -3 and jstack should be the cheapest. The functionality is implemented natively in JVM code. No intermediate structures are created - the VM prints everything itself while it walks through the stacks.

Both commands perform the same VM operation except that signal handler prints stack traces locally to stdout of Java process, while jstack receives the output from the target VM through IPC (Unix domain socket on Linux or Named Pipe on Windows).

jstack uses Dynamic Attach mechanism under the hood. You can also utilize Dynamic Attach directly if you wish to receive the stack traces as a plain stream of bytes.

import com.sun.tools.attach.VirtualMachine;
import sun.tools.attach.HotSpotVirtualMachine;
import java.io.InputStream;

public class StackTrace {

    public static void main(String[] args) throws Exception {
        String pid = args[0];
        HotSpotVirtualMachine vm = (HotSpotVirtualMachine) VirtualMachine.attach(pid);

        try (InputStream in = vm.remoteDataDump()) {
            byte[] buf = new byte[8000];
            for (int bytes; (bytes = in.read(buf)) > 0; ) {
                System.out.write(buf, 0, bytes);
            }
        } finally {
            vm.detach();
        }
    }
}

Note that all of the mentioned methods operate in a VM safepoint anyway. This means that all Java threads are stopped while the stack traces are collected.

Answer 2

The most performant option is likely to be the use of the ThreadMXBean.dumpAllThreads() API rather than requesting a text thread dump written to disk: http://docs.oracle.com/javase/7/docs/api/java/lang/management/ThreadMXBean.html#dumpAllThreads(boolean,%20boolean)

Of course, whether you can use that depends on whether you need a thread dump file, or just the data.