Java多线程start（）方法原理解析

/**
 * @data 2019/11/8 - 下午10:29
 * 描述：run()和start()
 */
public class StartAndRunMethod {
  public static void main(String[] args) {
    Runnable runnable = new Runnable() {
      @Override
      public void run() {
        System.out.println(Thread.currentThread().getName());
      }
    };
    runnable.run();

    new Thread(runnable).start();
  }
}

public synchronized void start() {
    /**
     * This method is not invoked for the main method thread or "system"
     * group threads created/set up by the VM. Any new functionality added
     * to this method in the future may have to also be added to the VM.
     *
     * A zero status value corresponds to state "NEW".
     */
    if (threadStatus != 0)
      throw new IllegalThreadStateException();

  /*
   * Java thread status for tools, default indicates thread 'not yet started'
   */
  private volatile int threadStatus;

 /* Notify the group that this thread is about to be started
     * so that it can be added to the group's list of threads
     * and the group's unstarted count can be decremented. */
    group.add(this);

boolean started = false;
    try {
      start0();
      started = true;
    } finally {
      try {
        if (!started) {
          group.threadStartFailed(this);
        }
      } catch (Throwable ignore) {
        /* do nothing. If start0 threw a Throwable then
         it will be passed up the call stack */
      }
    }
  }

/**
 * @data 2019/11/8 - 下午11:57
 * 描述：start不可以使用多次
 */
public class CantStartTwice {
  public static void main(String[] args) {
    Thread thread = new Thread();
    thread.start();
    thread.start();
  }
}