并发更新问题

Question

我有一个基本的java编程。问题是有2个站共用同一条跑道，让它作为站A（SA）和站B（SB）。当SA指定飞机着陆时，SB无法将任何飞机分配到着陆或离开，直到SA释放它为止。一旦SA降落跑道，它将停在停靠站上，我假设机场最多有4个停靠站。 问题是当我一起运行2个线程时，一旦我允许SA同时将飞机分配到跑道，SB也允许将飞机分配给跑道。在SA的飞机到达扩展坞并更新值后，SB也会到达扩展坞，扩展坞根本不会更新。任何人都可以解决我的问题吗？谢谢。我的代码将在下面显示：

ATC.java

package ccsd;
import java.io.*;
import java.net.*;

public class ATC implements Runnable
{
static Process test = new Process();
Process b;
int option;
int currentRunway;
int currentDockSpace;
int airplaneID;

BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));


 ATC (Process a) {

 b = a;

 }

public void run()
{
    try
    {
            System.out.println("Air Traffic Control");    
            System.out.println("1. Assign airplane to landing.");
            System.out.println("2. Assign airplane to departure.");
            System.out.println("Enter the option: ");
            option = Integer.parseInt(bufferedReader.readLine());
            if (option == 1){
                currentRunway = b.getCurrentRunway();
                currentDockSpace = b.getDockSpace();
                if (currentRunway == 0 && currentDockSpace < 5){
                    currentRunway = 1;
                    b.setCurrentRunway(currentRunway);
                    System.out.println("Input airplane id: ");
                    airplaneID = Integer.parseInt(bufferedReader.readLine());
                    b.setAirplaneID(airplaneID);
                    System.out.println("Currently airplane "+ b.getAirplaneID() + "is going land.");
                    System.out.println("Processing in... 10.. \n9..\n8..\n7..\n6..\n5..\n4..\n3..\n2..\n1.."); 
                    System.out.println("Airplane" + b.getAirplaneID() + " had been landed.");
                    b.dockIn();
                    b.setCurrentRunway(0);
                    System.out.println("Currently the run way is clear now and "+ b.getDockSpace() + " docking space used.");
                }
                else
                    System.out.println("Currently there is an airplane landing or lack docking space, please try again later."); 
                    run();
            }

            else if (option == 2){
                currentDockSpace = b.getDockSpace();
                if (currentDockSpace>0){
                System.out.println("Input airplane id: ");
                airplaneID = Integer.parseInt(bufferedReader.readLine());
                b.setAirplaneID(airplaneID);
                currentRunway = b.getCurrentRunway();
                    if (currentRunway == 0){
                        b.setCurrentRunway(1);       
                        System.out.println("Currently airplane "+ b.getAirplaneID() + "is departuring.");
                        System.out.println("Processing in... 10.. \n9..\n8..\n7..\n6..\n5..\n4..\n3..\n2..\n1.."); 
                        System.out.println("Airplane" + b.getAirplaneID() + " had been departured.");
                        b.dockOut();
                        b.setCurrentRunway(0);
                        System.out.println("Currently the run way is clear now and "+ b.getDockSpace() + " docking space used.");
                    }
                    else
                    {
                        System.out.println("Currently there is an airplane landing, please try again later.");
                        run();
                    }
              }
              else
                {
              System.out.println("Currently there is no any airplane in the docking, please try again later.");
              run();      
            }
    }        
    }
    catch(Exception e)
    {
        System.out.println(e);
    }
}

public static void main(String[] args) throws UnknownHostException, IOException, ClassNotFoundException, InterruptedException{

    Thread thread1 = new Thread(new ATC(test));

    thread1.start();

}

}

---

ATC2.java

package ccsd;

import java.io.*;
import java.net.*;

public class ATC2 implements Runnable
{
Process b;
int option;
int currentRunway;
int currentDockSpace;
int airplaneID;
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));


 ATC2 (Process a) {

 b = a;

 }

public void run()
{
    try
    {
            System.out.println("Air Traffic Control");    
            System.out.println("1. Assign airplane to landing.");
            System.out.println("2. Assign airplane to departure.");
            System.out.println("Enter the option: ");
            option = Integer.parseInt(bufferedReader.readLine());
            if (option == 1){
                currentRunway = b.getCurrentRunway();
                currentDockSpace = b.getDockSpace();
                if (currentRunway == 0 && currentDockSpace < 5){
                    b.setCurrentRunway(1);
                    System.out.println("Input airplane id: ");
                    airplaneID = Integer.parseInt(bufferedReader.readLine());
                    b.setAirplaneID(airplaneID);
                    System.out.println("Currently airplane "+ b.getAirplaneID() + "is going land.");
                    System.out.println("Processing in... 10.. \n9..\n8..\n7..\n6..\n5..\n4..\n3..\n2..\n1.."); 
                    System.out.println("Airplane" + b.getAirplaneID() + " had been landed.");
                    b.dockIn();
                    b.setCurrentRunway(0);
                    System.out.println("Currently the run way is clear now and "+ b.getDockSpace() + " docking space used.");
                }
                else
                    System.out.println("Currently there is an airplane landing or lack docking space, please try again later."); 
                    run();
            }

            else if (option == 2){
                currentDockSpace = b.getDockSpace();
                if (currentDockSpace>0){
                System.out.println("Input airplane id: ");
                airplaneID = Integer.parseInt(bufferedReader.readLine());
                b.setAirplaneID(airplaneID);
                currentRunway = b.getCurrentRunway();
                    if (currentRunway == 0){
                        b.setCurrentRunway(1);       
                        System.out.println("Currently airplane "+ b.getAirplaneID() + "is departuring.");
                        System.out.println("Processing in... 10.. \n9..\n8..\n7..\n6..\n5..\n4..\n3..\n2..\n1.."); 
                        System.out.println("Airplane" + b.getAirplaneID() + " had been departured.");
                        b.dockOut();
                        b.setCurrentRunway(0);
                        System.out.println("Currently the run way is clear now and "+ b.getDockSpace() + " docking space used.");
                    }
                    else
                    {
                        System.out.println("Currently there is an airplane landing, please try again later.");
                        run();
                    }
              }
              else
                {
              System.out.println("Currently there is no any airplane in the docking, please try again later.");
              run();      
            }
    }        
    }
    catch(Exception e)
    {
        System.out.println(e);
    }
}

public static void main(String[] args) throws UnknownHostException, IOException, ClassNotFoundException, InterruptedException{

    Thread thread2 = new Thread(new ATC2(ATC.test));

    thread2.start();

}

}

---

Process.java

package ccsd;

public class Process {
int airplaneID;
int currentRunway;
int dock;

   public synchronized void setAirplaneID(int airplaneID)
   {
this.airplaneID = airplaneID;       
   }

   public int getAirplaneID()
   {
    return airplaneID;
   }

   public synchronized void setCurrentRunway(int currentRunway)
   {
this.currentRunway = currentRunway;
   }

    public int getCurrentRunway()
    {
    return currentRunway;
    }

    public synchronized void dockIn()
    {
    dock++;
    }

    public synchronized void dockOut()
    {
    dock--;
    }

    public int getDockSpace()
    {
    return dock;
    }

}

我希望有人能一步一步告诉我该怎么做。感谢。

Answer 1

如何表示跑道限制有很多种可能性。

我个人喜欢排队很多东西 - 它们似乎符合我的心态。我从来没有使用过SynchronousQueue，但是从JavaDocs中，它可能就是你想要的。

您还可以使用容量为1的ArrayBockingQueue 。

YMMV。我打赌你会得到很多其他的选择。

Answer 2

您必须通过多个线程进行同步。最好的办法是为每条跑道使用计数信号量（java.util.concurrent.Semaphore）。也许甚至对于每个扩展坞也是如此。使用这种技术，您可以根据需要将任意数量的对象与任意数量的进程（线程）同步。