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，

能夠支援，2個生產者執行緒及10個消費者執行緒的阻塞呼叫（經常問！）

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1. 使用synchronized、wait和notify/notifyall來實現

package interview_test;
/**
 * 使用wait和notify/notifyall來實現
 * @author x1c
 *
 */

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

public class MyContainer1<T> {
	final private LinkedList<T> list = new LinkedList<>();
	final private int MAX = 10;
	private int count = 0;
	
	public synchronized void put(T t) {
		while (list.size() == MAX) {  //想想為什麼用while而不是if   while會再次檢查！
			try {
				this.wait(); //effective java一書中說wait 99.9%和 while一起使用,wait釋放鎖
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		list.add(t);
		++count;
		this.notifyAll(); //通知消費者執行緒進行消費
	}
	
	public synchronized T get() {
		T t = null;
		while (list.size() == 0) {
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		t = list.removeFirst(); //Removes and returns the first element from this list.
		count --;
		this.notifyAll();
		return t;
	}
	
	public static void main(String[] args) {
		MyContainer1<String> c = new MyContainer1<>();
		//啟動消費者執行緒
		for (int i = 0; i < 10; i++) { //10個消費者執行緒
			new Thread(()->{
				for (int j = 0; j < 4; j++) {
					System.out.println(Thread.currentThread().getName()+"-->"+c.get());
				}
			},"consumer"+i) .start();
		}
		
		System.out.println("等待2秒生產-開始");
		try {
			TimeUnit.SECONDS.sleep(2);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("等待2秒生產-結束");
		
		//啟動生產者執行緒
		for (int i = 0; i < 2; i++) { //2個生產者執行緒
			new Thread(()->{
				for (int j = 0; j < 8 ;j++) {
					c.put(Thread.currentThread().getName()+" "+j );
					System.out.println("生產者:"+Thread.currentThread().getName()+" "+j );
				}
			},"product"+i) .start();
		}
	}
}
 

2. 使用Lock、await和signalAll

package interview_test;
/**
 * 面試題：生產者和消費者 經常問
 * 使用Lock和Condition來實現
 *Condition方式可以更加精確的指定那些執行緒被喚醒
 * @author x1c
 * 總結：synchronized wait notifyall一起使用
 *     lock await signalAll 一起使用
 *
 */

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> list = new LinkedList<>();
	final private int MAX = 10;
	private int count = 0;
	
	private Lock lock = new ReentrantLock(); //Lock介面 java.util.concurrent.locks.Lock  ReentrantLock重入鎖
	private Condition producer = lock.newCondition(); //Condition介面 java.util.concurrent.locks.Condition
	private Condition consumer = lock.newCondition(); 
	
	public /*synchronized*/ void put(T t) {
		lock.lock();//
		while (list.size() == MAX) {  //想想為什麼用while而不是if   while會再次檢查！
			try {
				//this.wait(); //effective java一書中說wait 99.9%和 while一起使用,wait釋放鎖
				producer.await();//
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		list.add(t);
		++count;
//		this.notifyAll(); //通知消費者執行緒進行消費
		consumer.signalAll(); //精確叫醒消費者執行緒
	}
	
	public /*synchronized*/ T get() {
		T t = null;
		lock.lock();//
		while (list.size() == 0) {
			try {
//				this.wait();
				consumer.await();//
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		t = list.removeFirst(); //Removes and returns the first element from this list.
		count --;
//		this.notifyAll();
		consumer.signalAll(); //精確指定消費者執行緒消費
		return t;
	}
	
	public static void main(String[] args) {
		MyContainer2<String> c = new MyContainer2<>();
		//啟動消費者執行緒
		for (int i = 0; i < 10; i++) { //10個消費者執行緒
			new Thread(()->{
				for (int j = 0; j < 4; j++) {
					System.out.println(Thread.currentThread().getName()+"-->"+c.get());
				}
			},"consumer"+i) .start();
		}
		
		System.out.println("等待2秒生產-開始");
		try {
			TimeUnit.SECONDS.sleep(2);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("等待2秒生產-結束");
		
		//啟動生產者執行緒
		for (int i = 0; i < 2; i++) { //2個生產者執行緒
			new Thread(()->{
				for (int j = 0; j < 8 ;j++) {
					c.put(Thread.currentThread().getName()+" "+j );
					System.out.println("生產者:"+Thread.currentThread().getName()+" "+j );
				}
			},"product"+i) .start();
		}
	}
}
 

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