java併發每日一練

問題

使用 wait notify 實現一個隊列，隊列有2個方法，add 和 get 。add方法往隊列中添加元素，get方法往隊列中獲得元素。隊列必須是線程安全的。如果get執行時，隊列爲空，線程必須阻塞等待，直到有隊列有數據。如果add時，隊列已經滿，則add線程要等待，直到隊列有空閒空間。

答案

//這是一段錯誤的實現代碼
package java併發學習.自己實現線程安全的隊列;

import java.util.LinkedList;

/**
 * Created by h on 17-2-2.
 */
class MyQueue {
    int sum = 100;
    LinkedList<Integer> lls = new LinkedList<>();

    public Integer get() {
        if (lls.size() > 0) {
            int res = lls.get(0);
            lls.remove(0);
            return res;
        } else return -1;
    }

    public void put(int i) {
        lls.add(lls.size(), i);
    }
}

public class Main {
    public static void main(String[] args) {
        MyQueue q = new MyQueue();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10000; i++) {
                    if (q.lls.size() < 100)
                        q.put(i);
                    System.out.println("PUT " + i);
                }
            }
        });
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10000; i++) {
                    if (q.lls.size() > 0)
                        System.out.println("GET " + q.get());
                }
            }
        });
        t1.start();
        t2.start();
    }
}

解法

package java併發學習.自己實現線程安全的隊列;

import java.util.LinkedList;

/**
 * Created by h on 17-2-2.
 */
class MyQueue {
    int sum = 100;
    LinkedList<Integer> lls = new LinkedList<>();

    public Integer get() {
        synchronized (lls) {
            while (lls.size()<=0){
                try {
                    lls.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            lls.notify();
        }

        return lls.remove(0);
    }

    public void put(int i) {
        synchronized (lls){
            while (lls.size() >= sum){
                try {
                    lls.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            lls.notify();
            lls.add(i);
            System.out.println("put " + i);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        MyQueue q = new MyQueue();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10000; i++) {
                    System.out.println("get " + q.get());
                }
            }
        });
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10000; i++) {
                        q.put(i);

                }
            }
        });
        t1.start();
        t2.start();
    }
}