Question

Implement a solution java solution for creating two writer threads and four reader threads

Answer 1

Following is the source code :

/** WriterThread.java **/

public class WriterThread extends Thread
{
    private static int writers = 0; // number of writers

    private int number;
    private Library library;

    /**
     This is how to create a writer thread for the specified library.
     @param library braryli to which to write.
     */
    public WriterThread(Library library)
    {
        this.library = library;
        this.number = WriterThread.writers++;
    }

    /**
     Running the thread
     */
    public void run()
    {
        while (true)
        {
            final int THREAD_DELAY = 10000;
            try
            {
                Thread.sleep((int) (Math.random() * THREAD_DELAY));
            }
            catch (InterruptedException e) {}
            this.library.write(this.number);
        }
    }
}

/** ReaderThread.java **/

public class ReaderThread extends Thread
{
    private static int readers = 0;

    private int number;
    private Library library;

    /**
     This is how to create a reader thread for the library
     */
    public ReaderThread(Library library)
    {
        this.library = library;
        this.number = ReaderThread.readers++;
    }

    /**
     running a thread
     */
    public void run()
    {
        while (true)
        {
            final int THREAD_DELAY = 10000;
            try
            {
                Thread.sleep((int) (Math.random() * THREAD_DELAY));
            }
            catch (InterruptedException e) {}
            this.library.read(this.number);
        }
    }
}

/**Library.java **/

public class Library
{
    private int readers; // number of active readers

    /**
     Initializes the library.
     */
    public Library()
    {
        this.readers = 0;
    }

    /**
     Reading  from the library.

     @param number Number of the reader.
     */
    public void read(int number)
    {
        synchronized(this)
        {
            this.readers++;
            System.out.println("Reader thread" + number + " starts reading.");
        }

        final int THREAD_DELAY = 5000;
        try
        {
            Thread.sleep((int) (Math.random() * THREAD_DELAY));
        }
        catch (InterruptedException e) {}

        synchronized(this)
        {
            System.out.println("Reader thread" + number + " stops reading.");
            this.readers--;
            if (this.readers == 0)
            {
                this.notifyAll();
            }
        }
    }

    /**
     Writing to the library .

     @param number Number of the writer thread.
     */
    public synchronized void write(int number)
    {
        while (this.readers != 0)
        {
            try
            {
                this.wait();
            }
            catch (InterruptedException e) {}
        }
        System.out.println("Writer thread " + number + " starts writing.");

        final int DELAY = 5000;
        try
        {
            Thread.sleep((int) (Math.random() * DELAY));
        }
        catch (InterruptedException e) {}

        System.out.println("Writer thread" + number + " stops writing.");
        this.notifyAll();
    }



}

/** Test.java **/

public class Test {

    /**
     Start two reader thread and 4 writer threads from main class .

     */
    public static void main(String[] args)
    {
        {
            final int READERS = 2;
            final int WRITERS = 4;
            Library library = new Library();
            for (int i = 0; i < READERS; i++)
            {
                new ReaderThread(library).start();
            }
            for (int i = 0; i < WRITERS; i++)
            {
                new WriterThread(library).start();
            }
        }
    }
}