c1- n++ 线程安全性demo

UnsafeSequence

package com.dang.book2.chapter1;

/**
 * Created by Dangdang on 2018/7/16.
 * 非线程安全的数值生成器，非线程安全主要体现在 number++ 操作上，该操作并非原子性，包括3个连续动作
 * 从主存中取number -> 线程内存 number+1 -> 写回到主存number；<br>
 * 但由于执行很快，故本例的两个线程有可能未能体现出最终结果不等于99的现象
 */
public class UnsafeSequence {

    private int number;

    /**
     * 返回唯一数值，将在多线程环境下运行
     *
     * @return
     */
    public int getNext() {
        try {
            Thread.sleep(10L);
        } catch (InterruptedException e) {

        }
        return number++;
    }

}

SafeSequence

package com.dang.book2.chapter1;

public class SafeSequence {

    private int number;

    /**
     * 返回唯一数值，将在多线程环境下运行
     *
     * @return
     */
    public synchronized int getNext() {
        try {
            Thread.sleep(10L);
        } catch (InterruptedException e) {

        }
        return number++;
    }

}

demo

package com.dang.book2.chapter1;

/**
 * Created by Dangdang on 2018/7/16.
 */
public class SequenceDemo {

    public static void main(String[] args) {

        SequenceDemo demo = new SequenceDemo();

        //demo.unSafeTest();
        demo.safeTest();

    }

    public void unSafeTest() {
        //线程共享变量
        final UnsafeSequence sequence = new UnsafeSequence();

        //lambda 代替可以代替匿名内部类,也可直接将=右边表达式放到Thread参数中
        Runnable target = () -> {
            for (int i = 0; i < 50; i++) {
                int next = sequence.getNext();
                System.out.println(Thread.currentThread().getName() + ":" + next);
            }
        };

        Thread thread1 = new Thread(target);
        Thread thread2 = new Thread(target);
        thread1.start();
        thread2.start();
    }

    public void safeTest() {
        SafeSequence safeSequence = new SafeSequence();

        Runnable target2 = () -> {
            for (int i = 0; i < 50; i++) {
                int next = safeSequence.getNext();
                System.out.println(Thread.currentThread().getName() + ":" + next);
            }
        };

        Thread thread1 = new Thread(target2);
        Thread thread2 = new Thread(target2);
        thread1.start();
        thread2.start();
    }

}