code: package io.ray.test;
  
  import io.ray.api.ActorHandle;
  import io.ray.api.ObjectRef;
  import io.ray.api.Ray;
  import io.ray.runtime.util.SystemUtil;
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.lang.ProcessBuilder.Redirect;
  import java.util.ArrayList;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  import java.util.stream.Collectors;
  import org.testng.Assert;
  import org.testng.annotations.Test;
  
  @Test(groups = {"cluster"})
  public class MultiDriverTest extends BaseTest {
  
    private static final int DRIVER_COUNT = 10;
    private static final int NORMAL_TASK_COUNT_PER_DRIVER = 100;
    private static final int ACTOR_COUNT_PER_DRIVER = 10;
    private static final String PID_LIST_PREFIX = "PID: ";
  
    static int getPid() {
      return SystemUtil.pid();
    }
  
    public static class Actor {
  
      public int getPid() {
        return SystemUtil.pid();
      }
    }
  
    public static void main(String[] args) throws IOException {
      Ray.init();
  
      List<ObjectRef<Integer>> pidObjectList = new ArrayList<>();
      // Submit some normal tasks and get the PIDs of workers which execute the tasks.
      for (int i = 0; i < NORMAL_TASK_COUNT_PER_DRIVER; ++i) {
        pidObjectList.add(Ray.task(MultiDriverTest::getPid).remote());
      }
      // Create some actors and get the PIDs of actors.
      for (int i = 0; i < ACTOR_COUNT_PER_DRIVER; ++i) {
        ActorHandle<Actor> actor = Ray.actor(Actor::new).remote();
        pidObjectList.add(actor.task(Actor::getPid).remote());
      }
      Set<Integer> pids = new HashSet<>();
      for (ObjectRef<Integer> object : pidObjectList) {
        pids.add(object.get());
      }
      // Write pids to stdout
      System.out.println(
          PID_LIST_PREFIX + pids.stream().map(String::valueOf).collect(Collectors.joining(",")));
    }
  
    public void testMultiDrivers() throws InterruptedException, IOException {
      // This test case starts some driver processes. Each driver process submits some tasks and
      // collect the PIDs of the workers used by the driver. The drivers output the PID list
      // which will be read by the test case itself. The test case will compare the PIDs used by
      // different drivers and make sure that all the PIDs don't overlap. If overlapped, it means that
      // tasks owned by different drivers were scheduled to the same worker process, that is, tasks
      // of different jobs were not correctly isolated during execution.
      List<Process> drivers = new ArrayList<>();
      for (int i = 0; i < DRIVER_COUNT; ++i) {
        drivers.add(startDriver());
      }
  
      // Wait for drivers to finish.
      for (Process driver : drivers) {
        driver.waitFor();
        Assert.assertEquals(
            driver.exitValue(), 0, "The driver exited with code " + driver.exitValue());
      }
  
      // Read driver outputs and check for any PID overlap.
      Set<Integer> pids = new HashSet<>();
      for (Process driver : drivers) {
        try (BufferedReader reader =
            new BufferedReader(new InputStreamReader(driver.getInputStream()))) {
          String line;
          int previousSize = pids.size();
          while ((line = reader.readLine()) != null) {
            if (line.startsWith(PID_LIST_PREFIX)) {
              for (String pidString : line.substring(PID_LIST_PREFIX.length()).split(",")) {
                // Make sure the PIDs don't overlap.
                Assert.assertTrue(
                    pids.add(Integer.valueOf(pidString)),
                    "Worker process with PID " + line + " is shared by multiple drivers.");
              }
              break;
            }
          }
          int nowSize = pids.size();
          Assert.assertTrue(nowSize > previousSize);
        }
      }
    }
  
    private Process startDriver() throws IOException {
      ProcessBuilder builder = TestUtils.buildDriver(MultiDriverTest.class, null);
      builder.redirectError(Redirect.INHERIT);
      return builder.start();
    }
  }
  