为什么要将栈和程序计数器设置为线程私有的呢？前边说线程是cpu执行的基本单位，而cpu一般是使用时间片轮转方式轮询占用的，所以当当前线程cpu时间片使用完毕后，要让出cpu，等待下一次轮到自己的时候在调用。
那问题就来了，线程是如何知道之前执行到哪了？程序计数器就是为了记录之前让出cpu时执行到的地址，等下次再次执行时就可以从程序计数器中获取之前执行到的位置，继续向下执行。（程序计数器是不会记录native方法执行的地址的，它只记录java代码执行的地址），而栈则是存储现场的局部变量，一遍之后再次使用

package com.nxz.blog.otherTest;import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;public class TestThread {static class MyThread1 extends Thread {@Overridepublic void run() {System.out.println("extend-Thread："+this.getName());}}static class MyThread2 implements Runnable {@Overridepublic void run() {System.out.println("implements-Runnable:"+Thread.currentThread());}}static class MyThread3 implements Callable<String> {@Overridepublic String call() throws Exception {System.out.println("implements-Callable:"+Thread.currentThread());return "Callable接口";}}public static void main(String[] args) {MyThread1 t1 = new MyThread1();t1.start();Thread t2 = new Thread(new MyThread2());t2.start();FutureTask<String> futureTask = new FutureTask<>(new MyThread3());new Thread(futureTask).start();try {// 阻塞，等待执行完毕，并返回结果String res = futureTask.get();System.out.println(res);} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}System.out.println("main-Thread");}
}

extend-Thread:Thread-0
implements-Runnable:Thread[Thread-1,5,main]
implements-Callable:Thread[Thread-2,5,main]
Callable接口
main-Thread

    public final void wait(long timeout, int nanos) throws InterruptedException {if (timeout < 0) {throw new IllegalArgumentException("timeout value is negative");}if (nanos < 0 || nanos > 999999) {throw new IllegalArgumentException("nanosecond timeout value out of range");}if (nanos > 0) {timeout++;}wait(timeout);}

    static Queue queue;static class ProductThread extends Thread {@Overridepublic void run() {synchronized (queue) {if (queue.size() == 1) {// 假设队列最多存一个对象try {queue.wait();} catch (InterruptedException e) {e.printStackTrace();}}queue.add(new Object());queue.notifyAll();}}}static class ConsumerThread extends Thread {@Overridepublic void run() {synchronized (queue) {if (queue.isEmpty()) {try {queue.wait();} catch (InterruptedException e) {e.printStackTrace();}}queue.poll();queue.notifyAll();}}}

package com.nxz.blog.otherTest;public class TestThread002 {static class MyThread extends Thread{@Overridepublic void run() {System.out.println("myThread");}}public static void main(String[] args) throws InterruptedException {MyThread t1 = new MyThread();t1.setName("myThread");t1.start();// 如果注释掉 下边代码的话，main方法的输出应该会是  先main-thread 然后再试mythread，// 放开的话 main主线程就会等待t1线程执行完毕后，在向下运行t1.join();System.out.println("main-thread");}
}

    public void set(T value) {Thread t = Thread.currentThread();// 当调用ThreadLocal的set方法时，其实是获取的是当前线程Thread中的ThreadLocalMap变量，如果变量为null，则新建一个ThreadLocalMap，如果变量存在，则之间将当前线程和value存入定制的map中（ThreadLocalMap）ThreadLocalMap map = getMap(t);if (map != null)map.set(this, value);elsecreateMap(t, value);}// 从源码getMap中可以看出，其实获取的是当前线程中的threadLocals变量ThreadLocalMap getMap(Thread t) {return t.threadLocals;}void createMap(Thread t, T firstValue) {t.threadLocals = new ThreadLocalMap(this, firstValue);}

    public T get() {// ThreadLocal的get方法，同样是获取的是当前线程Thread中的threadLocals变量（也就是ThreadLocalMap类型的数据）Thread t = Thread.currentThread();ThreadLocalMap map = getMap(t);if (map != null) {ThreadLocalMap.Entry e = map.getEntry(this);if (e != null) {@SuppressWarnings("unchecked")T result = (T)e.value;return result;}}return setInitialValue();}