Can the openjdk 8 jvm use more than 4 cores?

问题

I've asked the question on unix.stackexchange as well...

Can the openjdk 8 (on ubuntu) run more than 4 threads

(i.e.: use the 8 cores available) on a system?

Edit: I have 12 Thread objects which run simultaneously (they all produce output) but the linux top program indicates there are only 4 cores occupied with the java process (when scaling from 1 Thread to 2, 3 and 4 I didn't have this problem)...

Edit2: top output:

%Cpu(s): 41.8 us

6982 ubuntu    20   0 8766844   1.7g  18684 S 352.0  11.6  26:07.56 java

lscpu output:

CPU(s):                          8
On-line CPU(s) list:             0-7
Thread(s) per core:              2
Core(s) per socket:              4
Socket(s):                       1

Edit3:

            Agent[] agentz = new Agent[4]; //implements Runnable

            agentz[0] = new Agent(botMovez[0], playerIndex);

            for (int i = 1; i < 4; i++) {

                agentz[i] = new Agent(botMovez[i], playerIndex, boardCopies[i - 1]);
            }

            Thread[] threadz = new Thread[4];

            for (int i = 0; i < 4; i++) {

                threadz[i] = new Thread(agentz[i]);

                threadz[i].start();
            }

            for (int i = 0; i < 4; i++) {

                try {

                    threadz[i].join();

                } catch (InterruptedException e) {

                    e.printStackTrace();
                }
            }

-> this code gets executed in a Runnable which is started like:

    (new Thread(new Calculator(this, performedMoves))).start();

Edit4:

public class Test {

    public static void main(String[] args) {

        Test test = new Test();

        TestAgent[] testAgentz = new TestAgent[8];

        Thread[] threadz = new Thread[8];

        for (int i = 0; i < 8; i++) {

            testAgentz[i] = test.new TestAgent();

            threadz[i] = new Thread(testAgentz[i]);

            threadz[i].start();
        }
        
        System.out.println("waiting to join...");

        for (int i = 0; i < 8; i++) {

            try {
                threadz[i].join();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        System.out.println("unreachable code");

    }

    private class TestAgent implements Runnable {

        @Override
        public void run() {
            while (true) {

            }
        }
    }

}

-> This code does occupy 800% cpu

So it must be either Spring boot or Tomcat...

I'm going to ask another question because this one is getting to cluttered...

回答1:

I see the output of lscpu give 2 threads per core. You don't have an 8 core machine. Try running something like cat /dev/urandom > /dev/null 8 times. Probably you sill don't go over 400%.

来源：https://stackoverflow.com/questions/65844362/can-the-openjdk-8-jvm-use-more-than-4-cores

标签

java

multithreading