Condition使用

面試題：寫一個固定容量同步容器，擁有put和get方法，以及getCount方法，
    能夠支持2個生產者線程以及10個消費者線程的阻塞調用

有兩種方法

1.使用wait和notify/notifyAll來實現

import java.util.LinkedList;
import java.util.concurrent.TimeUnit;

public class MyContainer1<T> {
    final private LinkedList<T> lists = new LinkedList<>();
    final private int MAX = 10; //最多10個元素
    private int count = 0;
    
    
    public synchronized void put(T t) {
        while(lists.size() == MAX) { //想想為什麼用while而不是用if？
            try {
                this.wait(); //effective java
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        
        lists.add(t);
        ++count;
        this.notifyAll(); //通知消費者線程進行消費
    }
    
    public synchronized T get() {
        T t = null;
        while(lists.size() == 0) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        t = lists.removeFirst();
        count --;
        this.notifyAll(); //通知生產者進行生產
        return t;
    }
    
    public static void main(String[] args) {
        MyContainer1<String> c = new MyContainer1<>();
        //啟動消費者線程
        for(int i=0; i<10; i++) {
            new Thread(()->{
                for(int j=0; j<5; j++) System.out.println(c.get());
            }, "c" + i).start();
        }
        
        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        //啟動生產者線程
        for(int i=0; i<2; i++) {
            new Thread(()->{
                for(int j=0; j<25; j++) c.put(Thread.currentThread().getName() + " " + j);
            }, "p" + i).start();
        }
    }
}

2.使用Lock和Condition來實現
 對比兩種方式，Condition的方式可以更加精確的指定哪些線程被喚醒

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

public class MyContainer2<T> {
    final private LinkedList<T> lists = new LinkedList<>();
    final private int MAX = 10; //最多10個元素
    private int count = 0;
    
    private Lock lock = new ReentrantLock();
    private Condition producer = lock.newCondition();
    private Condition consumer = lock.newCondition();
    
    public void put(T t) {
        try {
            lock.lock();
            while(lists.size() == MAX) { //想想為什麼用while而不是用if？
                producer.await();
            }
            
            lists.add(t);
            ++count;
            consumer.signalAll(); //通知消費者線程進行消費
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public T get() {
        T t = null;
        try {
            lock.lock();
            while(lists.size() == 0) {
                consumer.await();
            }
            t = lists.removeFirst();
            count --;
            producer.signalAll(); //通知生產者進行生產
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
        return t;
    }
    
    public static void main(String[] args) {
        MyContainer2<String> c = new MyContainer2<>();
        //啟動消費者線程
        for(int i=0; i<10; i++) {
            new Thread(()->{
                for(int j=0; j<5; j++) System.out.println(c.get());
            }, "c" + i).start();
        }
        
        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        //啟動生產者線程
        for(int i=0; i<2; i++) {
            new Thread(()->{
                for(int j=0; j<25; j++) c.put(Thread.currentThread().getName() + " " + j);
            }, "p" + i).start();
        }
    }
}