【題意】：開6條執行緒計算累加1 -> 10000000

【思路】：生產者-消費者 經典模型

1. 多個生產者負責生產(累加)作業
2. 生產者將生產結果存入共享倉庫中
3. 消費者（主執行緒）從共享倉庫中取出結果

/**
 * 多執行緒計算累加數
 */
public class Accumulate {
    public static void main(String[] args) {
        Storage storage = new Storage();
        // 為多個計算器物件建立執行緒
        Thread calThread1 = new Thread(new Calculate(1, storage), "Thread-1");
        Thread calThread2 = new Thread(new Calculate(2, storage), "Thread-2");
        Thread calThread3 = new Thread(new Calculate(3, storage), "Thread-3");
        Thread calThread4 = new Thread(new Calculate(4, storage), "Thread-4");
        Thread calThread5 = new Thread(new Calculate(5, storage), "Thread-5");
        Thread calThread6 = new Thread(new Calculate(6, storage), "Thread-6");

        calThread1.start();
        calThread2.start();
        calThread3.start();
        calThread4.start();
        calThread5.start();
        calThread6.start();

        // 列印最終結果
        storage.printTotal();
    }
}

/**
 * 計算器物件，負責計算start -> end
 */
class Calculate implements Runnable {
    private Storage storage;
    private long start;

    public Calculate(long start, Storage storage) {
        this.start = start;
        this.storage = storage;
    }

    @Override
    public void run() {
        long num = start;
        long sum = 0;
        while (num <= 10000000) {
            System.out.println(Thread.currentThread().getName() + " add num " + num);
            sum += num;
            num += 6;
        }
        // 執行緒計算完畢， 呼叫累加器進行累加
        storage.push(sum);
    }
}

/**
 * 倉庫物件，負責累加
 */
class Storage {
    private long total = 0;
    private int count = 0;

    public synchronized void push(long sum) {
        total += sum;
        count++;
        notifyAll();
    }

    public synchronized void printTotal() {
        while (count < 6) {
            try {
                System.out.println(Thread.currentThread().getName() + " is wait");
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("storage result = " + total);
    }
}