Question

I wrote a thread class that checks the socket connection to the server by sending a small string every one second.

begin() method executes the thread.

After connection is lost, the thread tries to connect again.

My question is if it’s ok to re-run by begin() the thread inside the run() method like I did (see below).

public void begin() {  
   Check = new Thread(this);
   Check.start();
}

@Override
public void run() {
   Thread thisThread = Thread.currentThread();
   while (Check==thisThread) {
      try {
         oos.writeObject("a");
         // oos.flush();

         synchronized (this) {
            while (pleaseWait) {
               try {
                  System.out.println("waiting");    
                  wait();
                  System.out.println("not waiting");      
               } 
               catch (Exception e) {
                  System.err.println("Thread is interrupted: "+e.getMessage());
               }
            }
         }
         sleep(1000);
         } catch (Exception ex) {
              v = new Visual("The connection is lost. The system will try to reconnect now.");
              this.end();
              try {
                 Server=ClientLogin.checkingServers(); //returns the reachable server string address
                 socket = new Socket(Server, ServerPort);
                 System.out.println("Connected: " + socket);
                 oos = new ObjectOutputStream(socket.getOutputStream());
                 begin();
                 v = new Visual("The system is reconnected.");
              }
              catch(UnknownHostException uhe){  
                 System.out.println("Host unknown: " + uhe.getMessage());
                 v = new Visual("The system has failed to reconnected.");
              }
              catch (IOException ioe) {
                 System.out.println("The system cannot connect to servers: " + ioe.getMessage());
                 v = new Visual("The system has failed to reconnected.");
              }
              catch (Exception e) {
                 System.out.println("The system has failed to reconnect: " + e.getMessage());
                 v = new Visual("The system has failed to reconnected.");
              }
          }
   }
}

public void end() {
   Check = null;
}

Answer 1

I don’t know any reason why that wouldn’t work, but it looks kinda messy. You may have to declare Check as volatile to ensure that the loop always reads the current value, for those times when the new thread overwrites it.

IMHO a better approach would be a separate “supervisor” thread which is responsible for starting one of these threads, and then uses Thread.join() to wait for it to die, at which point it can start it up again.

In this way your main thread’s logic can concentrate on exactly what it’s supposed to do, without needing to have any “self awareness”.