a java PoC for launching threads into CGroups

CGroupThreads.java

import java.io.IOException;
import java.lang.Runnable;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadFactory;

public class CGroupThreads {
	static class CGThread extends Thread {
		private final String cgroupName;
		private int osId;

		public CGThread(String cgroupName, Runnable r) {
			super(r);
			this.cgroupName = cgroupName;
		}
		
		public void run() {
			try {
				setup();
			} catch(IOException e) {
				throw new RuntimeException(e);
			}

			super.run();
		}

		private void setup() throws IOException {
			String tid = Files.readSymbolicLink(Paths.get("/proc/thread-self")).getFileName().toString();
			this.osId = Integer.parseInt(tid);
			Files.write(
				Paths.get("/sys/fs/cgroup/net_prio", cgroupName, "tasks"),
				Integer.toString(this.osId).getBytes()
			);
		}

		public int getOSId() {
			return this.osId;
		}
	}

	static class CGThreadFactory implements ThreadFactory {
		private final String cgroupName;

		public CGThreadFactory(String name) {
			this.cgroupName = name;
		}

		public Thread newThread(Runnable r) {
			return new CGroupThreads.CGThread(cgroupName, r);
		}
	}

	public static void main(String[] args) throws Exception {
		if(args.length == 0) {
			System.err.println("Please pass the desired CGroup name as an argument");
			System.exit(1);
		}
		ExecutorService exs = Executors.newFixedThreadPool(1, new CGThreadFactory(args[0]));

		exs.submit(() -> {
			System.out.println(((CGThread)Thread.currentThread()).getOSId());
		}).get();
		exs.shutdown();
	}
}