package javalearning;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
public class ThreadLocalDemo {
	/*定義了1個(gè)ThreadLocal<Integer>對(duì)象，
   *并復(fù)寫它的initialValue方法，初始值是3*/
	private ThreadLocal<Integer> tlA = new ThreadLocal<Integer>(){
		protected Integer initialValue(){
			return 3;
		}
	}
	;
	/* 
  private ThreadLocal<Integer> tlB = new ThreadLocal<Integer>(){
    protected Integer initialValue(){
      return 5;
    }
  };
  */
	/*設(shè)置一個(gè)信號(hào)量，許可數(shù)為1，讓三個(gè)線程順序執(zhí)行*/
	Semaphore semaphore = new Semaphore(1);
	private Random rnd = new Random();
	/*Worker定義為內(nèi)部類實(shí)現(xiàn)了Runnable接口,tlA定義在外部類中，
每個(gè)線程中調(diào)用這個(gè)對(duì)象的get方法，再調(diào)用一個(gè)set方法設(shè)置一個(gè)隨機(jī)值*/
	public class Worker implements Runnable{
		@Override
		    public void run(){
			try {
				Thread.sleep(rnd.nextint(1000));
				/*隨機(jī)延時(shí)1s以內(nèi)的時(shí)間*/
				semaphore.acquire();
				/*獲取許可*/
			}
			catch (InterruptedException e) {
				e.printStackTrace();
			}
			int valA = tlA.get();
			System.out.println(Thread.currentThread().getName() +" tlA initial val : "+ valA);
			valA = rnd.nextint();
			tlA.set(valA);
			System.out.println(Thread.currentThread().getName() +" tlA new   val: "+ valA);
			/*
      int valB = tlB.get();
      System.out.println(Thread.currentThread().getName() +" tlB initial val : "+ valB);
      valB = rnd.nextInt();
      tlA.set(valB);
      System.out.println(Thread.currentThread().getName() +" tlB 2  new val: "+ valB);
      */
			semaphore.release();
			/*在線程池中,當(dāng)線程退出之前一定要記得調(diào)用remove方法，因?yàn)樵诰€程池中的線程對(duì)象是循環(huán)使用的*/
			tlA.remove();
			/*tlB.remove();*/
		}
	}
	/*創(chuàng)建三個(gè)線程，每個(gè)線程都會(huì)對(duì)ThreadLocal對(duì)象tlA進(jìn)行操作*/
	public static void main(String[] args){
		ExecutorService es = Executors.newFixedThreadPool(3);
		ThreadLocalDemo tld = new ThreadLocalDemo();
		es.execute(tld.new Worker());
		es.execute(tld.new Worker());
		es.execute(tld.new Worker());
		es.shutdown();
	}
}

pool-1-thread-1 tlA initial val : 3
pool-1-thread-1 tlA new   val: -1288455998
pool-1-thread-3 tlA initial val : 3
pool-1-thread-3 tlA new   val: 112537197
pool-1-thread-2 tlA initial val : 3
pool-1-thread-2 tlA new   val: -12271334

public T get() {
  Thread t = Thread.currentThread();
  ThreadLocalMap map = getMap(t);
  if (map != null) {
    ThreadLocalMap.Entry e = map.getEntry(this);//這里的this是指當(dāng)前的ThreadLocal對(duì)象
    if (e != null) {
      @SuppressWarnings("unchecked")
      T result = (T)e.value;
      return result;
    }
  }
  return setInitialValue();
}