排好隊(duì),挨著跑

線程的順序執(zhí)行，有很多種方式，比如加鎖、用join、使用newSingleThreadExecutor等，最近碰到一個(gè)場(chǎng)景：主線程A中需要按順序執(zhí)行 a1、a2、a3、a4四個(gè)函數(shù)（即a1執(zhí)行完才可以開始a2），而 a1、a2、a3、a4每個(gè)函數(shù)中又開啟了多線程處理業(yè)務(wù)。

因此存在問題：a1執(zhí)行完的時(shí)候如何通知主線程，告訴a2?可以開啟了。

既然分析出了問題，那就好辦了，解決問題即可，這里使用java關(guān)鍵詞volatile

volatile：是一個(gè)變量修飾符，被用來修飾會(huì)被不同線程訪問和修改的變量。

解決思路：

1.定義全局變量并初始化為 flag = 0；

2.a1執(zhí)行完修改將變量改為1；a2執(zhí)行完將其改為2；以此類推；

3.主線程判斷某一步執(zhí)行完才開始下一步，否則sleep(300)

4.當(dāng)前線程是否執(zhí)行結(jié)束，使用原子計(jì)數(shù)器AtomicInteger

主線程示例

package com.mos.simple;
import com.mos.simple.thread.ThreadFour;import com.mos.simple.thread.ThreadOne;import com.mos.simple.thread.ThreadThree;import com.mos.simple.thread.ThreadTwo;import lombok.extern.slf4j.Slf4j;@Slf4jpublic class TheadDemo {
    public volatile static int FLAG = 0;

    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {            new TheadDemo().test(i);            System.out.println("--------------------i am dividing line---------------------");        }
    }
    public void test(int num) {        ThreadOne threadOne = new ThreadOne();        ThreadTwo threadTwo = new ThreadTwo();        ThreadThree threadThree = new ThreadThree();        ThreadFour threadFour = new ThreadFour();
        threadOne.test(num);        threadWait(1);        threadTwo.test(num);        threadWait(2);        threadThree.test(num);        threadWait(3);        threadFour.test(num);        threadWait(4);        FLAG = 0;    }
    private void threadWait(int x) {        while (FLAG != x) {            try {                Thread.sleep(300);            } catch (InterruptedException e) {                throw new RuntimeException(e);            }        }    }

}

a1()示例

package com.mos.simple.thread;
import com.mos.simple.TheadDemo;import lombok.extern.slf4j.Slf4j;
import java.util.HashMap;import java.util.Map;import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.Executors;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicInteger;
@Slf4jpublic class ThreadOne {

    public void test(int num) {        System.out.println("ThreadOne num is >> "+num);        //線程池        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(5, 5, 60L, TimeUnit.MILLISECONDS,                new ArrayBlockingQueue<>(100), Executors.defaultThreadFactory(),                new ThreadPoolExecutor.AbortPolicy());        AtomicInteger count = new AtomicInteger(0);        for (int i = 0; i < 100; i++) {            threadPoolExecutor.execute(() -> {                if (count.incrementAndGet() == 100) {                    TheadDemo.FLAG = 1;                }            });        }
    }}

執(zhí)行結(jié)果

?ThreadOne num is >> 0ThreadTwo num is >> 0ThreadThree num is >> 0ThreadFour num is >> 0--------------------i am dividing line---------------------ThreadOne num is >> 1ThreadTwo num is >> 1ThreadThree num is >> 1ThreadFour num is >> 1--------------------i am dividing line---------------------ThreadOne num is >> 2ThreadTwo num is >> 2ThreadThree num is >> 2ThreadFour num is >> 2--------------------i am dividing line---------------------ThreadOne num is >> 3ThreadTwo num is >> 3ThreadThree num is >> 3ThreadFour num is >> 3--------------------i am dividing line---------------------ThreadOne num is >> 4ThreadTwo num is >> 4ThreadThree num is >> 4ThreadFour num is >> 4--------------------i?am?dividing?line---------------------