JAVA練習ReentrantLock等， 用兩個線程同時操作，實現一次循環遍歷字符串

 

問題：

已知字符串abcdefghijk, 有兩個線程同時操作，實現一下一次循環遍歷出123456789。

例如：t1線程結果是1、 t2線程結果是2、 再是t1 = 3這樣的.、、、

 

本人使用ReentrantLock及Condition實現思路如下，歡迎多指點交流：

 

PS：show me code:

package com.lpz.test.interview;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 有字符串123456789這樣的, 有兩個線程同時執行,實現一下一次循環遍歷出123456789 例如：t1線程結果是1 t2線程結果是2 再是t1 = 3這樣的.
 *
 * @Author: lpz
 * @Date: 2019-04-25 16:48
 */
public class TwoThread {

    final static String str = "abcdefghijk";
    volatile AtomicInteger flag = new AtomicInteger(0);

    ReentrantLock lock = new ReentrantLock();
    Condition oddCondi = lock.newCondition();
    Condition evenCondi = lock.newCondition();


    public static void main(String[] args) {

        List<String> list = new ArrayList<>();
        for (int i = 0; i < str.length(); i++) {
            list.add(str.substring(i, i + 1));
        }
        System.out.println(list + " size: " + list.size());

        TwoThread twoThread = new TwoThread();
        for (int i = 0, num = list.size(); i <= num/2; i++) {
            // 偶數線程
            new Thread(() -> {
                twoThread.printEvenNum(list);
            }, "even").start();
            // 基數線程
            new Thread(() -> {
                twoThread.printOddNum(list);
            }, "odd").start();
        }


    }


    /**
     * 打印奇數odd
     */
    public void printOddNum(List<String> list) {
        try {
            lock.lockInterruptibly();
            while (flag.get() == list.size()) {
                return;
            }
            // 若偶數，奇數線程等待
            while (flag.get() % 2 == 0) {
                oddCondi.await();
            }
            //奇數來了，doing odd
            // 偶爾報異常：Exception in thread "odd" java.lang.IndexOutOfBoundsException: Index: 11, Size: 11
            // 但是上面有flag的return判斷啊。。。求解
            System.out.println(Thread.currentThread().getName() + " --- " + flag + " --- " + list.get(flag.get()));
            flag.incrementAndGet();
            // 喚起偶數線程
            evenCondi.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }


    /**
     * 打印偶數even
     */
    public void printEvenNum(List<String> list) {
        try {
            lock.lockInterruptibly();
            // 使用while代替if，防止虛假喚醒？
            while (flag.get() == list.size()) {
                return;
            }
            // 奇數情況下，偶數等待
            while (flag.get() % 2 == 1) {
                evenCondi.await();
            }
            // 偶數來了，doing even
            System.out.println(Thread.currentThread().getName() + " --- " + flag + " --- " + list.get(flag.get()));
            flag.getAndIncrement();
            // 喚起奇數線程
            oddCondi.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }


}

 

結果：

Connected to the target VM, address: '127.0.0.1:58542', transport: 'socket'
[a, b, c, d, e, f, g, h, i, j, k] size: 11
even --- 0 --- a
odd --- 1 --- b
even --- 2 --- c
odd --- 3 --- d
even --- 4 --- e
odd --- 5 --- f
even --- 6 --- g
odd --- 7 --- h
even --- 8 --- i
odd --- 9 --- j
even --- 10 --- k
Disconnected from the target VM, address: '127.0.0.1:58542', transport: 'socket'