Java多线程并发笔记03

示例程序01

public class RunThread extends Thread {
	
	//若属性不设置为volatile类型，那么每个方法体在执行的时候都会将成员变量从咱栈空间copy一份到堆空间的方法体内
	//在方法体内操作的是实际是这个变量的副本，而不是栈空间的里的那个变量。
	//加上了volatile变量后，那么变量就对各个线程是可见的了
	private volatile  boolean isRunning=true;
	
	private void setRunning(Boolean isRunning) {
		this.isRunning = isRunning;
	}
	
	@Override
	public void run() {
		System.out.println("进入run方法：");
		while(isRunning) {
			//。。
			//isRunning = false;
		}
		System.out.println("线程停止");
	}
	
	public static void main(String[] args) throws Exception {
		RunThread rt = new RunThread();
		rt.start();//分支线程阻塞式判断是否还在执行
		Thread.sleep(1000);
		rt.setRunning(false);//主线程中对变量进行更改
		System.out.println("isRunning 已经设置了false值");
		Thread.sleep(1000);
		System.out.println(rt.isRunning);
	}
	
}

 实例02

import java.util.concurrent.atomic.AtomicInteger;

/**
 * volatile 关键字不具备sunchronized关键字的原子性（同步）
 * 
 * */
public class VolatileNoAutomic extends Thread {
	
	private static AtomicInteger count = new AtomicInteger(0);
	
//	private static volatile int count = 0;
	//每个线程加1000
	public static void addCount() {
		for(int i = 0; i < 1000; i++) {
//			count++;
			count.incrementAndGet();
		}
		System.out.println(count);
	}
	
	@Override
	public void run() {
		addCount();
	}

	public static void main(String[] args) {
		VolatileNoAutomic[] vna = new VolatileNoAutomic[10];
		for(int i = 0; i < 10; i++) {
			vna[i] = new VolatileNoAutomic();
		}
		//10个线程
		for(int i = 0; i < 10; i++) {
			vna[i].start();
		}
	}
}

例子程序03 

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

public class AutomicUse {
	private static AtomicInteger count = new AtomicInteger(0);
	
	/*多个atomic在一个方法内是非原子性的，需要加synchronized进行修饰，	保证4个atomic整体原子性*/
	public synchronized int addCount() {
		try {
			Thread.sleep(10);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		count.addAndGet(1);
		count.addAndGet(2);
		count.addAndGet(3);
		count.addAndGet(4);
		return count.get();
	}
	

	public static void main(String[] args) {
		final AutomicUse use = new AutomicUse();
		List<Thread> ts = new ArrayList<Thread>();
		for(int i = 0; i < 100; i++) {
			ts.add(new Thread(new Runnable() {
				@Override
				public void run() {
					System.out.println(use.addCount());
				}
			}));
			
		}
		
		for(Thread t : ts){
			t.start();
		}
	}
	
	
}