java - Bully 算法的可疑代码输出

Question

我正在为 Java 中的 Bully 算法编写程序
这是代码:

package newbully;

public class NewBully {

    public static void main(String[] args) {
        int total_processes = 6;
        RunningThread[] t = new RunningThread[total_processes];
        for (int i = 0; i < total_processes; i++) {
            t[i] = new RunningThread(new Process(i+1, i+1), total_processes);//passing process id, priority, total no. of processes to running thread
        }
        try {
            Election.initialElection(t);
        } catch (Exception e) {
            System.out.println("Possibly you are using null references in array");
        }
        for (int i = 0; i < total_processes; i++) {
            new Thread(t[i]).start();//start every thread
        }
    }
}


package newbully;

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

public class RunningThread implements Runnable {

    private Process process;
    private int total_processes;
    ServerSocket[] sock;
    Random r;

    public Process getProcess() {
        return process;
    }

    public void setProcess(Process process) {
        this.process = process;
    }

    public RunningThread(Process process, int total_processes) {
        this.process = process;
        this.total_processes = total_processes;
        this.r = new Random();
        this.sock = new ServerSocket[total_processes];
    }

    synchronized private void recovery() {
        System.out.println("Process[" + this.process.getPid() + "]: -> Recovered from Crash");
        //Find current co-ordinator.
    }

    synchronized private void pingCoOrdinator() {
        try {
            if (Election.isPingFlag()) {
                synchronized (Election.lock) {
                    Election.lock.wait();
                }
            }
            if (!Election.isElectionFlag()) {
                Election.setPingFlag(true);
                System.out.println("Process[" + this.process.getPid() + "]: Are you alive?");
                Socket outgoing = new Socket(InetAddress.getLocalHost(), 12345);
                outgoing.close();
                Election.setPingFlag(false);
                synchronized (Election.lock) {
                    Election.lock.notifyAll();
                }
            }
        } catch (Exception ex) {
            //Initiate Election
            System.out.println("process[" + this.process.getPid() + "]: -> Co-Ordinator is down\nInitiating Election");
            Election.setElectionFlag(true);
            Election.setPingFlag(false);
            synchronized (Election.lock) {
                Election.lock.notifyAll();
            }
        }
    }

    synchronized private void executeJob() {
        int temp = r.nextInt(20);
        for (int i = 0; i <= temp; i++) {
            try {
                Thread.sleep(700);
            } catch (InterruptedException e) {
                System.out.println("Error Executing Thread:" + process.getPid());
                System.out.println(e.getMessage());
            }
        }
    }

    synchronized private boolean sendMessage() {
        boolean response = false;
        int i = 0;
        try {
            if (Election.isMessageFlag()) {
                synchronized (Election.lock) {
                    Election.lock.wait();
                }
            }
            Election.setMessageFlag(true);
            if (Election.isElectionFlag()) {
                for (i = this.process.getPid() + 1; i <= this.total_processes; i++) {
                    try {
                        Socket electionMessage = new Socket(InetAddress.getLocalHost(), 10000 + i);
                        System.out.println("Process[" + this.process.getPid() + "] -> Process[" + i + "]  responded to election message successfully");
                        electionMessage.close();
                        response = true;
                    } catch (Exception ex) {
                        System.out.println("Process[" + this.process.getPid() + "] -> Process[" + i + "] did not respond to election message");
                    }
                }
            }
            Election.setMessageFlag(false);
            synchronized (Election.lock) {
                Election.lock.notifyAll();
            }
        } catch (Exception ex1) {
            System.out.println(ex1.getMessage());
        }

        return response;
    }

    synchronized private void serve() {
        try {
            //service counter
            Socket incoming = null;
            ServerSocket s = new ServerSocket(12345);
            for (int counter = 0; counter < 10; counter++) {
                incoming = s.accept();
                System.out.println("Process[" + this.process.getPid() + "]:Yes");
                Scanner scan = new Scanner(incoming.getInputStream());
                PrintWriter out = new PrintWriter(incoming.getOutputStream(), true);
                if (scan.hasNextLine()) {
                    if (scan.nextLine().equals("Who is the co-ordinator?")) {
                        System.out.print("Process[" + this.process.getPid() + "]:");
                        out.println(this.process);
                    }
                }
            }
            //after serving 10 requests go down for random time
            this.process.setCoOrdinatorFlag(false);
            this.process.setDownflag(true);
            try {
                incoming.close();
                s.close();
                sock[this.process.getPid() - 1].close();
                Thread.sleep((this.r.nextInt(10) + 1) * 1000000);//going down
                recovery();
            } catch (InterruptedException e) {
                System.out.println(e.getMessage());
            }


        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        }
    }

    @Override
    public void run() {
        try {
            sock[this.process.getPid() - 1] = new ServerSocket(10000 + this.process.getPid());
        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        }
        while (true) {
            if (process.isCoOrdinatorFlag()) {
                //serve other processes
                serve();
            } else {
                while (true) {
                    //Execute some task
                    executeJob();

                    //Ping the co-ordinator
                    pingCoOrdinator();

                    if (Election.isElectionFlag()) {
                        if (!sendMessage()) {//elect self as co-ordinator
                            System.out.println("New Co-Ordinator: Process[" + this.process.getPid() + "]");
                            this.process.setCoOrdinatorFlag(true);
                            Election.setElectionFlag(false);
                            break;
                        }
                    }
                }
            }
        }
    }
}

package newbully;

public class Election {

    private static boolean pingFlag = false;
    private static boolean electionFlag = false;
    private static boolean messageFlag = false;
    public static final Object lock = new Object(); 

    public static boolean isMessageFlag() {
        return messageFlag;
    }

    public static void setMessageFlag(boolean messageFlag) {
        Election.messageFlag = messageFlag;
    }

    public static boolean isPingFlag() {
        return pingFlag;
    }

    public static void setPingFlag(boolean pingFlag) {
        Election.pingFlag = pingFlag;
    }

    public static boolean isElectionFlag() {
        return electionFlag;
    }

    public static void setElectionFlag(boolean electionFlag) {
        Election.electionFlag = electionFlag;
    }

    public static void initialElection(RunningThread[] t) {
        Process temp = new Process(-1, -1);
        for (int i = 0; i < t.length; i++) {
            if (temp.getPriority() < t[i].getProcess().getPriority()) {
                temp = t[i].getProcess();
            }
        }
        t[temp.pid - 1].getProcess().CoOrdinatorFlag = true;
    }
}

package newbully;

public class Process {

    int pid;
    boolean downflag,CoOrdinatorFlag;

    public boolean isCoOrdinatorFlag() {
        return CoOrdinatorFlag;
    }

    public void setCoOrdinatorFlag(boolean isCoOrdinator) {
        this.CoOrdinatorFlag = isCoOrdinator;
    }
    int priority;

    public boolean isDownflag() {
        return downflag;
    }

    public void setDownflag(boolean downflag) {
        this.downflag = downflag;
    }

    public int getPid() {
        return pid;
    }

    public void setPid(int pid) {
        this.pid = pid;
    }

    public int getPriority() {
        return priority;
    }

    public void setPriority(int priority) {
        this.priority = priority;
    }

    public Process() {
    }

    public Process(int pid, int priority) {
        this.pid = pid;
        this.downflag = false;
        this.priority = priority;
        this.CoOrdinatorFlag = false;
    }
}

这是输出:

//--When delay in executeJob() method is 100

Process[4]: Are you alive?
Process[6]:Yes
Process[4]: Are you alive?
Process[6]:Yes
Process[3]: Are you alive?
Process[6]:Yes
Process[5]: Are you alive?
Process[6]:Yes
Process[1]: Are you alive?
Process[6]:Yes
Process[4]: Are you alive?
Process[6]:Yes
Process[3]: Are you alive?
Process[6]:Yes
Process[3]: Are you alive?
Process[6]:Yes
Process[2]: Are you alive?
Process[6]:Yes
Process[5]: Are you alive?
Process[6]:Yes
Process[1]: Are you alive?
process[1]: -> Co-Ordinator is down
Initiating Election
Process[1] -> Process[2]  responded to election message successfully
Process[1] -> Process[3]  responded to election message successfully
Process[1] -> Process[4]  responded to election message successfully
Process[1] -> Process[5]  responded to election message successfully
Process[1] -> Process[6] did not respond to election message
Process[2] -> Process[3]  responded to election message successfully
Process[3] -> Process[4]  responded to election message successfully
Process[4] -> Process[5]  responded to election message successfully
Process[2] -> Process[4]  responded to election message successfully
Process[2] -> Process[5]  responded to election message successfully
Process[3] -> Process[5]  responded to election message successfully
Process[5] -> Process[6] did not respond to election message
New Co-Ordinator: Process[5]
New Co-Ordinator: Process[1]
Address already in use: JVM_Bind
Address already in use: JVM_Bind
Address already in use: JVM_Bind


 //--When delay in executeJob() method is 700
Process[3]: Are you alive?
Process[6]:Yes
Process[5]: Are you alive?
Process[6]:Yes
Process[2]: Are you alive?
Process[1]: Are you alive?
Process[6]:Yes
Process[6]:Yes
Process[5]: Are you alive?
Process[1]: Are you alive?
Process[6]:Yes
Process[6]:Yes
Process[4]: Are you alive?
Process[6]:Yes
Process[3]: Are you alive?
Process[6]:Yes
Process[2]: Are you alive?
Process[6]:Yes
Process[1]: Are you alive?
Process[6]:Yes
Process[4]: Are you alive?
process[4]: -> Co-Ordinator is down
Initiating Election
Process[4] -> Process[5]  responded to election message successfully
Process[4] -> Process[6] did not respond to election message
Process[5] -> Process[6] did not respond to election message
New Co-Ordinator: Process[5]
Process[1]: Are you alive?
Process[5]:Yes
Process[1]: Are you alive?
Process[5]:Yes
Process[3]: Are you alive?
Process[5]:Yes
Process[2]: Are you alive?
Process[5]:Yes
Process[1]: Are you alive?
Process[5]:Yes
Process[4]: Are you alive?
Process[5]:Yes
Process[2]: Are you alive?
Process[5]:Yes
Process[4]: Are you alive?
Process[5]:Yes
Process[3]: Are you alive?
Process[5]:Yes
Process[3]: Are you alive?
Process[5]:Yes
Process[2]: Are you alive?
process[2]: -> Co-Ordinator is down
Initiating Election
Process[2] -> Process[3]  responded to election message successfully
Process[2] -> Process[4]  responded to election message successfully
Process[2] -> Process[5] did not respond to election message
Process[2] -> Process[6] did not respond to election message
Process[3] -> Process[4]  responded to election message successfully
Process[3] -> Process[5] did not respond to election message
Process[3] -> Process[6] did not respond to election message
Process[1] -> Process[2]  responded to election message successfully
Process[1] -> Process[3]  responded to election message successfully
Process[1] -> Process[4]  responded to election message successfully
Process[1] -> Process[5] did not respond to election message
Process[1] -> Process[6] did not respond to election message
Process[2] -> Process[3]  responded to election message successfully
Process[2] -> Process[4]  responded to election message successfully
Process[2] -> Process[5] did not respond to election message
Process[2] -> Process[6] did not respond to election message
Process[4] -> Process[5] did not respond to election message
Process[4] -> Process[6] did not respond to election message
New Co-Ordinator: Process[4]
Process[3]: Are you alive?
Process[4]:Yes
Process[3]: Are you alive?
Process[4]:Yes
Process[1]: Are you alive?
Process[4]:Yes
Process[2]: Are you alive?
Process[4]:Yes
Process[1]: Are you alive?
Process[4]:Yes
Process[2]: Are you alive?
Process[4]:Yes
Process[2]: Are you alive?
Process[4]:Yes
Process[2]: Are you alive?
Process[4]:Yes
Process[3]: Are you alive?
Process[4]:Yes
Process[1]: Are you alive?
Process[4]:Yes
Process[3]: Are you alive?
process[3]: -> Co-Ordinator is down
Initiating Election
Process[3] -> Process[4] did not respond to election message
Process[3] -> Process[5] did not respond to election message
Process[3] -> Process[6] did not respond to election message
New Co-Ordinator: Process[3]
New Co-Ordinator: Process[2]
Address already in use: JVM_Bind
Address already in use: JVM_Bind
Address already in use: JVM_Bind
Address already in use: JVM_Bind
Address already in use: JVM_Bind

最后我开始遇到 Address already in use: JVM_Bin 异常。
另外，如果我们在thow异常(exception)之前与OUPUT的最新选举协调员核对，请在询问 is co-ordinator alive?之前选择两次
我敢肯定，当协调员去世时，我已经为它提供了足够的延迟，这样它就不会在两者之间醒来。
当我给予额外的交易时，程序会继续进行，否则它会在中间停止。
那么为什么一定会出现这个问题呢？

我找到了异常的原因
发生这种情况是因为如果您在异常消息之前仔细查看输出，它已经选择了协调器 2ce。
每当一个线程被选为协调者时，它都会在端口 12345 上打开一个 ServerSocket。
由于它发生在 2ce 它可能会引发异常。
但我不明白......为什么它选择了2ce？

Answer 1

您在这两种情况下的错误消息都是“地址已在使用中:JVM_Bind”。

此消息通常是 java.net.BindException 的一部分，当您尝试创建/打开 Socket 并且端口已在使用中时会抛出该异常。在这种情况下，您可能会尝试两次打开或创建相同的套接字。

这可能会发生，因为在打开和关闭套接字之间，异常会停止调用 socket.close()。在这种情况下，当您创建一个到选举领导者的套接字时，但是由于主机“崩溃”了一个异常被抛出，因此 close() 永远不会被调用。

我认为您需要添加该行

选举消息.close();到这部分发送消息的 catch 子句。

try {
    Socket electionMessage = new Socket(InetAddress.getLocalHost(), 10000 + i);
    System.out.println("Process[" + this.process.getPid() + "] -> Process[" + i + "]  responded to election message successfully");
    electionMessage.close();
    response = true;
} catch (Exception ex) {
//Add close here
    System.out.println("Process[" + this.process.getPid() + "] -> Process[" + i + "] did not respond to election message");
}

另外，我建议将 close 添加到所有其他相关的 catch 子句中，以防在其他地方发生这种情况，并且始终是避免相关问题的好习惯。
我还建议在每个地方明确指定要捕获的异常，以免被其他陷阱捕获。

我希望这是一个好的起点。

编辑以回应第一条评论

我认为您“锁定”线程的方式存在问题。您依靠 boolean 标志来告诉您已到达代码中的特定点。但是 boolean 标志本身不受同步块(synchronized block)的控制，也不受代码上的任何其他锁的控制。因此，多个线程可以传递锁并导致意外事件，例如多次尝试打开同一个套接字。

您正在使用带有对象的代码来锁定

if (Election.isMessageFlag()) {
    synchronized (Election.lock) {
        Election.lock.wait();
    }
}
Election.setMessageFlag(true);
if (Election.isElectionFlag()) {
   // Do Stuff
   // Open/close Sockets etc
}
Election.setMessageFlag(false);
synchronized (Election.lock) {
    Election.lock.notifyAll();
}

也就是说，在设置标志之前(在下一行!)，多个线程可能会通过第一个 if 语句以使后续线程等待。

但是，如果您改用 ReentrantLock，则应使用如下代码:

lock.lock();  // block until condition holds
try {
  // Do Stuff
  // OPen CLose Sockets etc
} finally {
  lock.unlock()
}

显然，您可能仍需要设置一些标志来说明选举是否正在进行，但请确保使用真正的锁来保护正在运行的代码，例如ReentrantLock，或在适当的同步块(synchronized block)内。

希望这可以帮助