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(); /* 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 */ } } } private native void start0(); /** * If this thread was constructed using a separate * <code>Runnable</code> run object, then that * <code>Runnable</code> object's <code>run</code> method is called; * otherwise, this method does nothing and returns. * <p> * Subclasses of <code>Thread</code> should override this method. * * @see #start() * @see #stop() * @see #Thread(ThreadGroup, Runnable, String) */ @Override public void run() { if (target != null) { target.run(); } }另外,还需要注意一下,执行start()方法的顺序不代表线程启动的顺序。
Thread的run方法和start方法
thread调用start()方法,可以理解为,start()方法通知“线程规划器”此线程已经准备就绪,等待调用线程对象的run()方法。这个过程其实就是让系统安排一个时间来调用Thread中的run()方法,也就是使线程得到运行,启动线程,具有异步执行的效果。如果直接调用代码thread.run()方法,就不是异步执行了,而是同步,那么此线程对象并不交给“线程规划器”来进行处理,而是由main主线程来调用run()方法,也就是必须等run()方法中的代码执行完后才可以执行后面的代码。源代码如下: