JUC併發編程學習筆記（三）生產者和消費者問題

生產者和消費者問題

synchronized版-> wait/notify

juc版->Lock

面試：單例模式、排序演算法、生產者和消費者、死鎖

生產者和消費者問題 Synchronized版

package org.example.pc;

public class A {
    public static void main(String[] args) {
        Date date = new Date();
        new Thread(()->{
            for (int i = 0; i < 20; i++) {
                date.increment();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 20; i++) {
                date.decrement();
            }
        },"B").start();
    }
}
//判斷等待、業務、通知
class Date{
    private int number = 0;

    public synchronized void increment(){
        if (number!=0){
            try {
                //不等於0就讓該線程等待
                this.wait();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }

        number++;
//        列印加完後的值
        System.out.println(Thread.currentThread().getName()+"=>"+number);
//        通知其他線程，我完成了
        this.notify();
    }
    public synchronized void decrement(){
        if (number!=1){
            try {
                this.wait();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
        number--;
        System.out.println(Thread.currentThread().getName()+"=>"+number);
        this.notify();
    }

}

存在的問題:A、B、C、D四個線程

線上程中判斷業務完成喚醒等待應該使用while迴圈判斷，而非if判斷，因為if判斷值判斷一次，線上程中存在一種狀態叫虛假喚醒。

JUC版生產者和消費者問題

代碼實現

package org.example.pc;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

//判斷等待、業務、通知
public class Date {
    private int number = 0;
    private Lock lock = new ReentrantLock();
    private Condition inCondition = lock.newCondition();

    public void increment() {

        try {
            lock.lock();
            while (number != 0) {
                inCondition.await();
            }
            number++;
//        列印加完後的值
            System.out.println(Thread.currentThread().getName() + "=>" + number);
//        通知其他線程，我完成了

            inCondition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }



    }

    public void decrement() {

        try {
            lock.lock();
            while (number != 1) {
                inCondition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName() + "=>" + number);
            inCondition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }


    }

}

Condition 精準的通知喚醒線程

在傳統併發編程中，通過notifily喚醒線程後所有線程都是隨機獲取到資源的，JUC中可以通過Condition來精準的控制要喚醒哪一個線程資源。任何一個新技術的出現都不會只是為了實現之前已有的效果

代碼實現

package org.example.pc;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class C {
    public static void main(String[] args) {
        DateC dateC = new DateC();
        new Thread(()->{
            for (int i = 0; i < 10; i++) dateC.plantA();
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) dateC.plantB();
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) dateC.plantC();
        },"C").start();
    }

}

class DateC {
    private int number = 1;
    private Lock lock = new ReentrantLock();
    private Condition inCondition1 = lock.newCondition();
    private Condition inCondition2 = lock.newCondition();
    private Condition inCondition3 = lock.newCondition();

   public void plantA(){
       try {
           lock.lock();
           while (number!=1){
               inCondition1.await();
           }
           System.out.println(Thread.currentThread().getName());
           number=2;
           inCondition2.signal();
       }catch (Exception e){
           e.printStackTrace();
       }finally {
           lock.unlock();
       }
   }
    public void plantB(){
        try {
            lock.lock();
            while (number!=2){
                inCondition2.await();
            }
            System.out.println(Thread.currentThread().getName());
            number=3;
            inCondition3.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
    public void plantC(){
        try {
            lock.lock();
            while (number!=3){
                inCondition3.await();
            }
            System.out.println(Thread.currentThread().getName());
            number=1;
            inCondition1.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
}