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Java synchronized線程交替運(yùn)行實(shí)現(xiàn)過(guò)程詳解

更新時(shí)間：2020年11月05日 15:00:12 作者：程序員吉爾

這篇文章主要介紹了Java synchronized線程交替運(yùn)行實(shí)現(xiàn)過(guò)程詳解,文中通過(guò)示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友可以參考下

背景

用兩個(gè)線程交替輸出A-Z和1-26，即一個(gè)線程輸出A-Z，另一個(gè)線程輸出1-26

而且是交替形式

線程1輸出A——線程二輸出1
線程1輸出B——線程二輸出2
線程1輸出C——線程二輸出3

以此類推

分析

主要考察線程之間的通信，思路就是創(chuàng)建兩個(gè)線程

在一個(gè)線程輸出一個(gè)內(nèi)容之后，自己進(jìn)入阻塞，去喚醒另一個(gè)線程

另一個(gè)線程同樣，輸出一個(gè)內(nèi)容之后，自己進(jìn)入阻塞，去喚醒另一個(gè)線程

代碼實(shí)現(xiàn)（一）

public class AlternateCover {

  public static void main(String[] args) {

    final char[] arrLetter = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
    final String[] arrNumber = {"1","2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17","18","19","20","21","22","23","24","25","26"};

    threadRun(arrLetter, arrNumber);
  }

  private static void threadRun(char[] arrLetter,String[] arrNumber){

    final Object lock = new Object();// 設(shè)置一個(gè)鎖對(duì)象

    // print arrNumber
    new Thread(() -> {
      synchronized (lock) {
        for (String a : arrNumber) {
          System.out.print( a);
          try {
            lock.notify();// 喚醒其他等待的線程 此處喚醒 arrLetter
            lock.wait();// arrNumber自己進(jìn)入等待 讓出CPU資源和鎖資源
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }
        lock.notify();
      }
    }, "arrNumber ").start();

    // print arrLetter
    new Thread(() -> {
      synchronized (lock) {// 獲取對(duì)象鎖
        for (char a : arrLetter) {
          System.out.print(a);
          try {
            lock.notify();// 喚醒其他等待的線程 此處喚醒 arrNumber
            lock.wait();// arrLetter自己進(jìn)入等待 讓出CPU資源和鎖資源
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }
        lock.notify();// 最后那個(gè)等待的線程需要被喚醒，否則程序無(wú)法結(jié)束
      }
    }, "arrLetter ").start();

  }
}

運(yùn)行一下，確實(shí)實(shí)現(xiàn)了交替輸出，但是多運(yùn)行幾次，就會(huì)發(fā)現(xiàn)問(wèn)題

有時(shí)候是數(shù)字先輸出，有時(shí)候是字母先輸出

即兩個(gè)線程誰(shuí)先啟動(dòng)的順序是不固定的

倘若試題中再加一句，必須要字母先輸出，怎么辦？

代碼實(shí)現(xiàn)（二）

/**
 * 交替掩護(hù) 必須保證大寫字母先輸出
 */
public class AlternateCover {

  public static volatile Boolean flg = false;// 誰(shuí)先開(kāi)始的標(biāo)志 volatile修飾目的是讓該值修改對(duì)所有線程可見(jiàn)，且防止指令重排序
  public static void main(String[] args) {

    final char[] arrLetter = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
    final String[] arrNumber = {"1","2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17","18","19","20","21","22","23","24","25","26"};

    threadRun(arrLetter, arrNumber);
  }

  private static void threadRun(char[] arrLetter,String[] arrNumber){

    final Object lock = new Object();// 鎖對(duì)象

    // print arrLetter
    new Thread(() -> {
      synchronized (lock) {
        if (!flg){ // 如果flg是false 就將值設(shè)為true
          flg = true;
        }
        for (char a : arrLetter) {
          System.out.print(a);// 輸出內(nèi)容
          try {
            lock.notify();// 喚醒在等待的其他線程中的一個(gè)（此處也只有另一個(gè)）
            lock.wait();// 自己進(jìn)入等待 讓出CPU資源和鎖資源
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }
        lock.notify();// 最后那個(gè)等待的線程需要被喚醒，否則程序無(wú)法結(jié)束
      }
    }, "arrLetter").start();

    // print arrNumber
    new Thread(() -> {
      synchronized (lock) {
        if (!flg){// 倘若是該線程先執(zhí)行，那么flg次數(shù)還是false 就先等著
          try {
            lock.wait();
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }

        for (String a : arrNumber) {
          System.out.print( a);
          try {
            lock.notify();
            lock.wait();
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }
        lock.notify();
      }
    }, "arrNumber").start();

  }

}

如此問(wèn)題可以得到解決，但有更優(yōu)(裝)雅（B）的解決辦法

CountDownLatch實(shí)現(xiàn)

/**
 * 交替掩護(hù) 必須保證大寫字母先輸出
 */
public class AlternateCover {

  private static CountDownLatch count = new CountDownLatch(1);// 計(jì)數(shù)器容量為1
  public static void main(String[] args) {

    final char[] arrLetter = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
    final String[] arrNumber = {"1","2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17","18","19","20","21","22","23","24","25","26"};

    threadRun(arrLetter, arrNumber);
  }

  private static void threadRun(char[] arrLetter,String[] arrNumber){

    final Object lock = new Object();

    // print arrLetter
    new Thread(() -> {
      synchronized (lock) {// 獲取對(duì)象鎖
        count.countDown();// 對(duì)計(jì)數(shù)器進(jìn)行遞減1操作，當(dāng)計(jì)數(shù)器遞減至0時(shí)，當(dāng)前線程會(huì)去喚醒阻塞隊(duì)列里的所有線程（只針對(duì)count）
        for (char a : arrLetter) {
          System.out.print(a);
          try {
            lock.notify();// 喚醒其他等待的線程 此處喚醒 arrNumber
            lock.wait();// arrLetter自己進(jìn)入等待 讓出CPU資源和鎖資源
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }
        lock.notify();// 最后那個(gè)等待的線程需要被喚醒，否則程序無(wú)法結(jié)束
      }
    }, "arrLetter ").start();

    // print arrNumber
    new Thread(() -> {
      synchronized (lock) {
        try {
          count.await();// 如果該線程先執(zhí)行 阻塞當(dāng)前線程，將當(dāng)前線程加入阻塞隊(duì)列
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        for (String a : arrNumber) {
          System.out.print( a);
          try {
            lock.notify();// 喚醒其他等待的線程 此處喚醒 arrLetter
            lock.wait();// arrNumber自己進(jìn)入等待 讓出CPU資源和鎖資源
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }
        lock.notify();
      }
    }, "arrNumber ").start();

  }

}

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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