1.并发编程挑战-上下文切换

package com.qdb.thinkv.thread.base;

/** 
 * 问题：多线程一定快吗？不一定，通过调整 count分别设置 比如1w 和 1亿 进行比较
 * 思考：如何减少上下文切换?
 */
public class ConcurrencyTest {
    public static final long count=1000000000L;
    public static void main(String[] args) throws InterruptedException {
        concurrency();
        seriai();
    }
    
    public static void concurrency() throws InterruptedException{
        long start=System.currentTimeMillis();
        Thread thread=new Thread(new Runnable(){
            public void run() {
                int a=0;
                for (long i = 0; i < count; i++) {
                    a+=5;
                }
            }
        });
        thread.start();
        int b=0;
        for (long i = 0; i < count; i++) {
            b--;
        }
        thread.join();
        long time=System.currentTimeMillis()-start;
        System.out.println("concurrency"+time+"ms,b="+b);
    }
    
    public static void seriai(){
        long start=System.currentTimeMillis();
        int a=0;
        for (long i = 0; i < count; i++) {
            a+=5;
        }
        long time=System.currentTimeMillis()-start;
        System.out.println("seriai"+time+"ms,a="+a);
        start=System.currentTimeMillis();
        int b=0;
        for (long i = 0; i < count; i++) {
            b--;
        }
        time=System.currentTimeMillis()-start;
        System.out.println("seriai"+time+"ms,b="+b+",a="+a);
    }
}