学习Java,为什么我没有得到一些线程的重叠？

Question

我尝试了以下代码:

/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;


    public class Main {
        static int i = 0;

    public static void main(String[] args) {

        new Thread(t1).start();
        new Thread(t2).start();
        new Thread(t3).start();
        new Thread(t4).start();
        new Thread(t5).start();
        new Thread(t6).start();
    }

    private static void countMe(String name){
        i++;
        System.out.println("Current Counter is: " + i + ", updated by: " + name);
    }

    private static Runnable t1 = new Runnable() {
        public void run() {
            try{
                for(int i=0; i<2; i++){
                    countMe("t1");
                }
            } catch (Exception e){}

        }
    };

    private static Runnable t2 = new Runnable() {
        public void run() {
            try{
                for(int i=0; i<2; i++){
                    countMe("t2");
                }
            } catch (Exception e){}
       }
    };
        private static Runnable t3 = new Runnable() {
        public void run() {
            try{
                for(int i=0; i<2; i++){
                    countMe("t3");
                }
            } catch (Exception e){}
       }
    };
        private static Runnable t4 = new Runnable() {
        public void run() {
            try{
                for(int i=0; i<2; i++){
                    countMe("t4");
                }
            } catch (Exception e){}
       }
    };
        private static Runnable t5 = new Runnable() {
        public void run() {
            try{
                for(int i=0; i<2; i++){
                    countMe("t5");
                }
            } catch (Exception e){}
       }
    };
        private static Runnable t6 = new Runnable() {
        public void run() {
            try{
                for(int i=0; i<2; i++){
                    countMe("t6");
                }
            } catch (Exception e){}
       }
    };
} 

并且在ideone上得到了输出: Current Counter is: 1, updated by: t1 Current Counter is: 2, updated by: t1 Current Counter is: 3, updated by: t2 Current Counter is: 4, updated by: t2 Current Counter is: 5, updated by: t3 Current Counter is: 6, updated by: t3 Current Counter is: 7, updated by: t4 Current Counter is: 8, updated by: t4 Current Counter is: 9, updated by: t5 Current Counter is: 10, updated by: t5 Current Counter is: 11, updated by: t6 Current Counter is: 12, updated by: t6 似乎一切都以线性方式进行,即按照我创建它们的顺序逐个称为函数countMe的线程.多线程意味着它们可能会出现故障.我在这里失踪了什么？我运行的机器(我在ideone.com上试过)的配置是这样的吗,它运行线程按顺序创建？

Answer 1

线程创建很昂贵.可能发生的是,当你完成启动线程2时,线程1已经完成.当线程3开始做它的事情时,线程2已经完成.等等.

在线程函数的开头插入一个六方循环屏障并看到它们竞争(可能甚至会失去一些i增量,因为i++不保证是原子的).

如果这还不足以可靠地触发竞赛,那么让线程做更多工作.