1、start方法执行流程

  1. 检查线程状态，只有在NEW状态的线程才能继续，否则会抛出IllegalThreadStateException()
  2. 被加入线程组
  3. 调用start0()方法启动线程
  1.  public synchronized void start() {
  2.         /**
  3.          * This method is not invoked for the main method thread or "system"
  4.          * group threads created/set up by the VM. Any new functionality added
  5.          * to this method in the future may have to also be added to the VM.
  6.          *
  7.          * A zero status value corresponds to state "NEW".
  8.          */
  9.         if (threadStatus != 0)
  10.             throw new IllegalThreadStateException();
  12.         /* Notify the group that this thread is about to be started
  13.          * so that it can be added to the group's list of threads
  14.          * and the group's unstarted count can be decremented. */
  15.         group.add(this);
  17.         boolean started = false;
  18.         try {
  19.             start0();
  20.             started = true;
  21.         } finally {
  22.             try {
  23.                 if (!started) {
  24.                     group.threadStartFailed(this);
  25.                 }
  26.             } catch (Throwable ignore) {
  27.                 /* do nothing. If start0 threw a Throwable then
  28.                   it will be passed up the call stack */
  29.             }
  30.         }
  31.     }