我是在产生线程并导致 memory 泄漏吗？

Question

I am converting a C++ program to Java for same implementation as a learning exercise and this java has a lot of things I am not yet familiar with, I had a long break in my work in the field.

Well here is the code:

public class MythicQuestDriver {
    
    public static void clrscr(){

        //Clears Screen in java

        try {

            if (System.getProperty("os.name").contains("Windows"))

                new ProcessBuilder("cmd", "/c", "cls").inheritIO().start().waitFor();

            else

                Runtime.getRuntime().exec("clear");

        } catch (IOException | InterruptedException ex) {}

    }
    

    public static void main(String[] args) {
    
    int x = 0;  
        
    MythicClock ElflordsTimepiece = new MythicClock(7,7,7);
    
    ElflordsTimepiece.printMythicClockDetails();
    
    do {
    new MainGameThread();
    clrscr();
    

    }while(x != '5');
}}

the clear screen function is from https://intellipaat.com/community/294/java-clear-the-console

and here is the thread class I slightly modified:

package MythicQuestGame;

import java.lang.*;

public class MainGameThread implements Runnable{
    
    Thread t;

    MainGameThread() {

          t = new Thread(this);
          System.out.println("Executing " + t.getName());
       
          // this will call run() fucntion
          t.start();
            
          /* interrupt the threads
          if (!t.interrupted()) {
             t.interrupt();
          }*/
          
          // block until other threads finish
          try {  
             t.join();
          } catch(InterruptedException e) {}
       }
    
    
    @Override
    public void run() {
        
        
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("thread ran");
        
        // TODO Auto-generated method stub
        
    }

}

and when I run I get a second like tiker but it goes thread1 thread2 thread3... I know I am running an infinte loop and that is by design as I am working towards an interupt like getch in c++ from: Last Question

So I have not got to the interupt thread join stuff yet, but am trying to follow the intent of what happens in my C++ code. I am interested to know if I need a destructor method or does the way threads work does it get its memory footprint removed after it runs because if I run a thread a second or 3 times a second or more it is gonna generate so many threads, but it would not matter if they are all destroyed after they run?

in my c++ program the implementation runs like this:

int main() {
    std::atomic<bool> interrupted;
    char x;

  do {
        interrupted.store(false);

        // create a new thread that does stuff in the background

        std::thread timerThread([&]()
            {

                while (!interrupted)
                {

            // does game stuff moves monsters 
            // checks for random encounters every aprox 15 sec
            // runs a clearscreen every 15 seconds and refresh output
            // hosts enemy attacks if in encounter
            // updates clock timer one sec every 3  passes
            // runs every .3 seconds

            }});
            x = _getch();
        //take input without waiting for an enterkey pressed
       // upon input interrupt thread 


        interrupted.store(true);
        timerThread.join();

    // here the program does things like:
    //based on input does character actions like move or attack
    // takes almost second sleep and adds one second to clock timer
    // runs a clear screen and new output

    

    } while (x != '5'); // exit condition
}

Answer 1

If I correctly understand, you're trying to achieve a temporized screen clearing, right?

In Java there's no such thing as destructors , specially when talking about threads where scheduling and thread's memory is mainly handled by the JVM itself (unless you're using shared objects like monitors ), so I think the problem in your code is how you're spawning threads. You should try to do that this way:

MainGameThread constructor

MainGameThread(){
    System.out.println("Executing " + t.getName());
}

MythicQuestDriver.java

...
// Creates the Runnable just once
MainGameThread runnable = new MainGameThread();
do {
    // Use the same Runnable for each thread you want to spawn
    Thread t = new Thread(runnable);

    // Start the thread and immediately stop and wait for its conclusion
    t.start();
    t.join();

    // Clear the screen
    clrscr();
} while (x != 5)

With that said, I do not think you should spawn threads in a loop at all, unless you know exactly how many threads will spawn.

Moreover, by starting a thread and then immediately stopping in order to wait for its conclusion you're really doing something that makes threads useless: in other words, you should reconsider your game's logic and adapt it to the way Java works, and not viceversa. For a simple example like the one you asked, a thread is not even necessary, you should place your game's logic inside the main loop and clear the screen once its execution ends, eventually using threads for complementary jobs!