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?
}
}
This question is related to
java
multithreading
threadpool
executorservice
executors
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.
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
There is the way of current thread getting:
Thread t = Thread.currentThread();
After you have got Thread class object (t) you are able to get information you need using Thread class methods.
Thread ID gettting:
long tId = t.getId(); // e.g. 14291
Thread name gettting:
String tName = t.getName(); // e.g. "pool-29-thread-7"
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.
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
Source: Stackoverflow.com