The busy waiting technique (also known as busy-looping or spinning) consists of a loop that checks a condition (typically, a flag condition). For example, the following loop waits for a service to start:

private volatile boolean serviceAvailable;
...
while (!serviceAvailable) {}

Java 9 introduced the Thread.onSpinWait() method. This is a hotspot that gives the JVM a hint that the following code is in a spin loop:

while (!serviceAvailable) {
  Thread.onSpinWait();
}

If we add this while loop in a context, then we obtain the following class:

public class StartService implements Runnable {

  private volatile boolean serviceAvailable;

  @Override
  public void run() {
    System.out.println("Wait for service to be available ...");

    while (!serviceAvailable) {
      // Use a spin-wait hint (ask the processor to
      // optimize the resource)
      // This should perform better if the underlying
      // hardware supports the hint
      Thread.onSpinWait();
    }

    serviceRun();
  }

  public void serviceRun() {
    System.out.println("Service is running ...");
  }

  public void setServiceAvailable(boolean serviceAvailable) {
    this.serviceAvailable = serviceAvailable;
  }
}

And, we can easily test it (do not expect to see the effect of onSpinWait()):

StartService startService = new StartService();
new Thread(startService).start();

Thread.sleep(5000);

startService.setServiceAvailable(true);