Use semaphore to implement monitor

Question

I want to use Semaphore to implement Monitor. I create 2 class. Buffer and ThreadDemo. In class Buffer, I create method put() and get() ( I get code from this page)

public void put(int input) throws InterruptedException {
    monitorSemaphore.acquire();
    boolean acquired = false;
    while (numberInBuffer == size) {
        // Equivalent of wait()
        if (acquired) {
            dec();
            notifyCalled.release();
        }
        inc();
        monitorSemaphore.release();
        notifyCalled.acquire();
        monitorSemaphore.acquire();
        acquired = true;
    }

    // Critical section
    buffer[last] = input;
    last = (last + 1) % size;
    numberInBuffer++;

    // Equivalent of notifyAll()
    for (int i = val(); i > 0; i--) {
        dec();
        notifyCalled.release();
    }

    monitorSemaphore.release();
}

public int get() throws InterruptedException {
    monitorSemaphore.acquire();

    boolean acquired = false;
    while (numberInBuffer == 0) {
        // Equivalent of wait()
        if (acquired) {
            dec();
            notifyCalled.release();
        }
        inc();
        monitorSemaphore.release();
        notifyCalled.acquire();
        monitorSemaphore.acquire();
        acquired = true;
    }

    // Critical section
    int temp = buffer[start];
    start = (start + 1) % size;
    numberInBuffer--;

    // Equivalent of notifyA(ll)
    for (int i = val(); i > 0; i--) {
        dec();
        notifyCalled.release();
    }

    monitorSemaphore.release(); 

    return temp;
}

In class TestThread, I create Thread-T1, Thread-T2. But I can't call put and Get in class Buffer.

public class TestThread extends Thread {
private Thread t;
   private String threadName;

   public TestThread(String name) {
       threadName = name;
       System.out.println("Creating " +  threadName );
   }

   public void run() {
      System.out.println("Running " +  threadName );
      try {
            put(2);//I can't call this method
            Thread.sleep(5000);
            get(); //
            Thread.sleep(5000);
         } catch (InterruptedException e) {
         System.out.println("Thread " +  threadName + " interrupted.");
     }
     System.out.println("Thread " +  threadName + " exiting.");
   }


   public void start ()
   {
      System.out.println("Starting " +  threadName );
      if (t == null)
      {
         t = new Thread (this, threadName);
         t.start ();
      }
   }


public static void main(String[] args) {

      TestThread T1 = new TestThread( "Thread-1");
      T1.start();

      TestThread T2 = new TestThread( "Thread-2");
      T2.start();

}}

And if my code in class TestThread incorrect, please show me. Thanks!

Answer 1

I think... Let's assume if you define the get() and put() method in Buffer class. Then you should initialize the class instance first before you call the in-class methods. Like the code below:

public class TestThread extends Thread {
   private Thread t;
   private String threadName;
   private Buffer buffer;

   public TestThread(String name, Buffer buffer) {
       threadName = name;
       this.buffer = buffer;
       System.out.println("Creating " +  threadName );
   }

   public void run() {
      System.out.println("Running " +  threadName );
      try {
            buffer.put(2);//I can't call this method
            Thread.sleep(5000);
            buffer.get(); //
            Thread.sleep(5000);
         } catch (InterruptedException e) {
         System.out.println("Thread " +  threadName + " interrupted.");
     }
     System.out.println("Thread " +  threadName + " exiting.");
   }
}