Obtaining the thread ID for Java threads in Linux

Question

I have a Java application where some threads are created (via new Thread()). Using ps I can see they have different thread IDs (LWP column) and I would like to obtain those IDs from within the Java application.

In most of the posts related to this topic that I have found (e.g., this one), the solution is to use ManagementFactory.getRuntimeMXBean().getName().

Using that method, however, gives me the PID of the main thread (even if I call it from one of the threads), so it is not really solving my problem.

Is there any way to obtain the thread ID for every single Thread created by an application?

Would it be possible to use JNI to accomplish it? If somehow I could interface to a C function where I could call syscall(__NR_gettid), that could solve my problem. I really do not care about portability, so I am totally okay with a solution that would only work for a Linux machine.

UPDATE: I have actually solved my problem by using JNI. Details are explained in my answer. Thank you all for your suggestions/comments.

Answer 1

In the end, I found the JNI way to be the best one to solve my problem. As a reference, I post the code and build instructions for it (based on the example at Wikipedia):

Java class responsible to interface to the C code (GetThreadID.java):

public class GetThreadID {
    public static native int get_tid();

    static {
        System.loadLibrary("GetThreadID");
    }
}

C file responsible to obtain the thread ID (GetThread.c):

#include <jni.h>
#include <syscall.h>
#include "GetThreadID.h"

JNIEXPORT jint JNICALL
Java_GetThreadID_get_1tid(JNIEnv *env, jobject obj) {
    jint tid = syscall(__NR_gettid);
    return tid;
}

An example of how to use GetThreadID class:

class Main {
    public static void main(String[] args) {
        int tid = GetThreadID.get_tid();
        System.out.println("TID=" + tid);
    }
}

And finally, the build instructions (javah automatically generates GetThreadID.h):

JAVA_HOME=$(readlink -f /usr/bin/javac | sed "s:bin/javac::")
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.
javac GetThreadID.java
javah GetThreadID

gcc -I${JAVA_HOME}/include -fPIC -shared GetThreadID.c -o libGetThreadID.so
javac Main.java
java Main

Answer 2

This blog post provides a method of mapping from java thread ids to LWP ids.

The gist of it seems to be that the NLWP id maps to the java thread id.