Obtaining the Thread Id for Java Threads in Linux

Obtaining the thread ID for Java threads in Linux

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

How to obtain the JVM thread name/id through the known PID/TID

Use jstack <PID>

"Thread-0" prio=10 tid=0x00002aaab01c3800 nid=0x246d runnable [0x00000000423c7000]
    ^ name             ^ Java thread id       ^ native (OS) thread id

How to find a Java thread running on Linux with ps -axl?

Use

jps -v

for finding your java process. Sample Output:

3825 RemoteMavenServer -Djava.awt.headless=true -Xmx512m -Dfile.encoding=MacRoman
6172 AppMain -Didea.launcher.port=7533 -Didea.launcher.bin.path=/Applications/IntelliJ IDEA 10.app/bin -Dfile.encoding=UTF-8
6175 Jps -Dapplication.home=/Library/Java/JavaVirtualMachines/1.6.0_31-b04-411.jdk/Contents/Home -Xms8m

Then use

jstack 6172

(6172 is id of your process) to get stack of threads inside jvm. Thread priority could be found from it. Sample output:

.....
"main" **prio=5** tid=7ff255800800 nid=0x104bec000 waiting on condition [104beb000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at au.com.byr.Sample.main(Sample.java:11)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

..... 

Enjoy!

EDIT: If application running under different user than yourself (typical case on production and other non-local environments) then jps/jstack should be run via sudo. Examples:

sudo jps -v

sudo jstack 6172

Matching between Java Thread and native Linux thread

thank all of you very much!

It seems that one of the easiest way to get such a behavior is to pass ZERO as threadId and expect thread with such a call being affined to a core you wish.

Of course there is another way to affine a thread to a core ( from Java PL ) but you have to decide upon cpu_set_t type substitution as well as its size.

How to get thread id from a thread pool?

Using Thread.currentThread():

private class MyTask implements Runnable {
    public void run() {
        long threadId = Thread.currentThread().getId();
        logger.debug("Thread # " + threadId + " is doing this task");
    }
}

The difference between Thread.currentThread().getId() and Process.myTid() in Android

I believe that there are two types of threads in a Java environment:

• Native Thread: which is managed by the hosted OS.
• Java Thread: which is managed by the JVM and is communicated with the native thread.

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