How to get thread id from a thread pool?
Solution 1
Using Thread.currentThread()
:
private class MyTask implements Runnable {
public void run() {
long threadId = Thread.currentThread().getId();
logger.debug("Thread # " + threadId + " is doing this task");
}
}
Solution 2
The accepted answer answers the question about getting a thread id, but it doesn't let you do "Thread X of Y" messages. Thread ids are unique across threads but don't necessarily start from 0 or 1.
Here is an example matching the question:
import java.util.concurrent.*;
class ThreadIdTest {
public static void main(String[] args) {
final int numThreads = 5;
ExecutorService exec = Executors.newFixedThreadPool(numThreads);
for (int i=0; i<10; i++) {
exec.execute(new Runnable() {
public void run() {
long threadId = Thread.currentThread().getId();
System.out.println("I am thread " + threadId + " of " + numThreads);
}
});
}
exec.shutdown();
}
}
and the output:
burhan@orion:/dev/shm$ javac ThreadIdTest.java && java ThreadIdTest
I am thread 8 of 5
I am thread 9 of 5
I am thread 10 of 5
I am thread 8 of 5
I am thread 9 of 5
I am thread 11 of 5
I am thread 8 of 5
I am thread 9 of 5
I am thread 10 of 5
I am thread 12 of 5
A slight tweak using modulo arithmetic will allow you to do "thread X of Y" correctly:
// modulo gives zero-based results hence the +1
long threadId = Thread.currentThread().getId()%numThreads +1;
New results:
burhan@orion:/dev/shm$ javac ThreadIdTest.java && java ThreadIdTest
I am thread 2 of 5
I am thread 3 of 5
I am thread 3 of 5
I am thread 3 of 5
I am thread 5 of 5
I am thread 1 of 5
I am thread 4 of 5
I am thread 1 of 5
I am thread 2 of 5
I am thread 3 of 5
Solution 3
You can use Thread.getCurrentThread.getId(), but why would you want to do that when LogRecord objects managed by the logger already have the thread Id. I think you are missing a configuration somewhere that logs the thread Ids for your log messages.
Solution 4
If you are using logging then thread names will be helpful. A thread factory helps with this:
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
public class Main {
static Logger LOG = LoggerFactory.getLogger(Main.class);
static class MyTask implements Runnable {
public void run() {
LOG.info("A pool thread is doing this task");
}
}
public static void main(String[] args) {
ExecutorService taskExecutor = Executors.newFixedThreadPool(5, new MyThreadFactory());
taskExecutor.execute(new MyTask());
taskExecutor.shutdown();
}
}
class MyThreadFactory implements ThreadFactory {
private int counter;
public Thread newThread(Runnable r) {
return new Thread(r, "My thread # " + counter++);
}
}
Output:
[ My thread # 0] Main INFO A pool thread is doing this task
Solution 5
If your class inherits from Thread, you can use methods getName
and setName
to name each thread. Otherwise you could just add a name
field to MyTask
, and initialize it in your constructor.
user2012801
Open source projects: Java HTML compressor/minifier jQuery loading mask plugin Chrome extensions: A whole bunch Feel free to contact me at: [email protected]
Updated on July 08, 2022Comments
-
user2012801 almost 2 years
I have a fixed thread pool that I submit tasks to (limited to 5 threads). How can I find out which one of those 5 threads executes my task (something like "thread #3 of 5 is doing this task")?
ExecutorService taskExecutor = Executors.newFixedThreadPool(5); //in infinite loop: taskExecutor.execute(new MyTask()); .... private class MyTask implements Runnable { public void run() { logger.debug("Thread # XXX is doing this task");//how to get thread id? } }
-
petrbel over 9 yearsthis is actually not the desired answer; one should use
% numThreads
instead -
CorayThan over 8 years@petrbel He's answering the question title perfectly, and the thread id is close enough in my opinion when the OP requests "something like 'thread #3 of 5".
-
Rag over 8 yearsAre Java thread IDs guaranteed to be contiguous? If not, your modulo won't work correctly.
-
Burhan Ali over 8 years@BrianGordon Not sure about a guarantee, but the code seems to nothing more than incrementing an internal counter: hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/…
-
Rag over 8 yearsSo if two thread pools were initialized simultaneously, the threads in one of those thread pools might have IDs of, for example, 1, 4, 5, 6, 7 and in that case you would have two different threads with the same "I am thread n of 5" message.
-
Matheus Azevedo almost 8 years@BrianGordon Thread.nextThreadID() is synchronized, so this wouldn't be a problem, right?
-
Rag almost 8 years@MatheusAzevedo That has nothing to do with it.
-
Joshua Pinter over 4 yearsNote, an example output of
getId()
is14291
where asgetName()
gives youpool-29-thread-7
, which I would argue is more useful.