java - 如何使用多线程聚合两个 Web 服务？

Question

有两个 Web 服务在提供实时库存的应用程序中运行。我必须编写一个java多线程程序从这两个接口(interface)读取库存并计算总库存。

前置条件:两个线程都必须立即启动。

我尝试使用下面的代码来解决这个问题。请检查并告诉我这是否正确。还有另一种可用的替代方法。

package com.app.thread;

public class InventoryThread {

    public static void main(String a[]) throws InterruptedException {

        Inventory inv = new Inventory();
        InventoryInterface1 i1 = new InventoryInterface1(inv);
        InventoryInterface2 i2 = new InventoryInterface2(inv);

        Thread t1 = new Thread(i1, "T1");
        Thread t2 = new Thread(i2, "T2");

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

        t1.join();
        t2.join();

        System.out.println(inv.getInventory());
    }
}

class Inventory {

    private long inventory;

    public long getInventory() {
        return inventory;
    }

    public void setInventory(long inventory) {
        this.inventory = inventory;
    }
}

class InventoryInterface1 implements Runnable {

    private Inventory inv;

    public InventoryInterface1(Inventory inv) {
        this.inv = inv;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + " running");
        synchronized (inv) {            
            System.out.println(Thread.currentThread().getName() + " updates inventory");
            inv.setInventory(inv.getInventory() + 100);         
        }
    }
}

class InventoryInterface2 implements Runnable {
    private Inventory inv;

    public InventoryInterface2(Inventory inv) {
        this.inv = inv;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + " running");
        synchronized (inv) {
            try {
                System.out.println(Thread.currentThread().getName() + " waiting..");
                while(inv.getInventory() <= 0){
                    inv.wait();
                }               
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + " updates inventory");
            inv.setInventory(inv.getInventory() + 200);
            System.out.println(Thread.currentThread().getName() + " notifies");
            inv.notifyAll();
        }
    }
}

Answer 1

将 Inventory.inventory 更改为 AtomicLong。这样你就不需要同步 InventoryInterface1 & InventoryInterface2

中的 Inventory 实例

class Inventory {

    private AtomicLong inventory = new AtomicLong();

    public long getInventory() {
        return inventory.longValue();
    }

    public void incrementInventory(long inventory) {
        inventory.addAndGet(inventory);
    }
}

问题是在 Java 中读取和写入 long 不需要是原子的。 AtomicLong 的 addAndGet 是一个原子操作。

这里修改了InventoryInterface1和InventoryInterface2

class InventoryInterface1 implements Runnable {

    private Inventory inv;

   public InventoryInterface1(Inventory inv) {
        this.inv = inv;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + " running");
        System.out.println(Thread.currentThread().getName() + " updates  inventory");
        inv.incrementInventory(100);         

    }
}



  class InventoryInterface2 implements Runnable {

    private Inventory inv;

    public InventoryInterface2(Inventory inv) {
        this.inv = inv;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + " running");
        System.out.println(Thread.currentThread().getName() + " updates inventory");
        inv.incrementInventory(200);
    }
}