import java.io.*;
import java.util.*;
 
/**Class scheduler: implements the synchronized methods, startread, endread,
 * startwrite and endwrite.
 * @author Kg2s
 */
public class scheduler{
    private int num_readers, num_writers, resource;
    public scheduler() {
        num_readers = 0;
        num_writers = 0;
        resource = -1;
    }
    /**Waits until the writers, if any, finish using the resource
     * then increment num_readers and print out the current status
     *@param thread_id : the current thread id, used in printing the status
     */
    public synchronized void startread(int thread_id){
        while(num_writers!=0) {
            try {
                wait();
            } catch(Exception e){}
        }
        num_readers++;
        String s = String.format("Reader[%d]:(startread) num_readers= %d, num_writers = %d, resource = %d",thread_id,num_readers,num_writers,resource );
        System.out.println(s);       
 
    }
    /**Decrement num_readers then print out the current status and notify others
     *that read is complete
     *@param thread_id : the current thread id, used in printing the status
     */
 
    public synchronized void endread(int thread_id){
        num_readers--;
        String s = String.format("Reader[%d]:(endread) num_readers= %d, num_writers = %d, resource = %d",thread_id,num_readers,num_writers,resource );
        System.out.println(s);
        notifyAll();
 
    }
    /**Waits until all the other writers and readers, if any, finish using the resource
     * then increment num_writers and print out the current status
     *@param thread_id : the current thread id, used in printing the status
     */    
 
    public synchronized void startwrite(int thread_id){
 
        while(num_writers!=0 || num_readers !=0) {
            try {
                wait();                
            } catch(Exception e){}
        }
        num_writers++;
        resource = thread_id;
        String s = String.format("Writer[%d]:(startwrite) num_readers= %d, num_writers = %d, resource = %d",thread_id,num_readers,num_writers,resource );
        System.out.println(s);        
 
    }
    /**Decrement num_writers then print out the current status and notify others
     *that write is complete
     *@param thread_id : the current thread id, used in printing the status
     */
    public synchronized void endwrite(int thread_id){
        num_writers--;
        String s = String.format("Writer[%d]:(endwrite) num_readers= %d, num_writers = %d, resource = %d",thread_id,num_readers,num_writers,resource );
        System.out.println(s);
        notifyAll();
    }   
 
}