线程详解
1.我们都知道一个线程的启动，只有两种方式第一种是继承Thread方法，重写run方法，第二种是实现Runnable，叫个Thread执行
2. 通过代码我们可以看到线程启动方法中，有start0(), 真正去启动一个线程，发现这个方法只是native修饰的方法，这边拓展一下什么是native修饰的方法

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 */
            }
        }
    }

拓展：Native Method，查阅英文文献的解释，"A native method is a Java method whose implementation is provided by non-java code."，准确的说非java实现的方法，主要为了加载文件和动态链接库，可以直接操作系统属性
3. 通过jni实现start0，内部初始化线程，最终会执行，vmSymbols::run_method_name()：即"run"；，也是java线程中run方法

线程的生命周期：初始化(new) --> 可运行状态(start) --> 运行状态（run）& 子状态暂停和阻塞 --> 销亡

具体业务：异步操作，FutureTask，里面有实现Runnable方法