Java多線程併發筆記03 volatile Automatic

示例程序01

public class RunThread extends Thread {
	
	//若屬性不設置爲volatile類型，那麼每個方法體在執行的時候都會將成員變量從咱棧空間copy一份到堆空間的方法體內
	//在方法體內操作的是實際是這個變量的副本，而不是棧空間的裏的那個變量。
	//加上了volatile變量後，那麼變量就對各個線程是可見的了
	private volatile  boolean isRunning=true;
	
	private void setRunning(Boolean isRunning) {
		this.isRunning = isRunning;
	}
	
	@Override
	public void run() {
		System.out.println("進入run方法：");
		while(isRunning) {
			//。。
			//isRunning = false;
		}
		System.out.println("線程停止");
	}
	
	public static void main(String[] args) throws Exception {
		RunThread rt = new RunThread();
		rt.start();//分支線程阻塞式判斷是否還在執行
		Thread.sleep(1000);
		rt.setRunning(false);//主線程中對變量進行更改
		System.out.println("isRunning 已經設置了false值");
		Thread.sleep(1000);
		System.out.println(rt.isRunning);
	}
	
}

 實例02

import java.util.concurrent.atomic.AtomicInteger;

/**
 * volatile 關鍵字不具備sunchronized關鍵字的原子性（同步）
 * 
 * */
public class VolatileNoAutomic extends Thread {
	
	private static AtomicInteger count = new AtomicInteger(0);
	
//	private static volatile int count = 0;
	//每個線程加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個線程
		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);
	
	/*多個atomic在一個方法內是非原子性的，需要加synchronized進行修飾，	保證4個atomic整體原子性*/
	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();
		}
	}
	
	
}