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Troubleshooting Question

Thread Synchronization with equal sharing

Simon Leung
Simon Leung asked
Last Modified: 2020-11-25
In the code below, four threads are supposed to take turns to buy the ticket. However, it seems that only 2 threads buys more tickets than other.

Any idea how to communicate among the threads such that each one take turn to buy ?


class Buyer3 extends Thread {
   TicketPool pool;// declare total ticket and initialized it to 100 
     boolean neverBrought= true;
   Buyer3(TicketPool pool)
      this.pool = pool;
   public void run() //override run() here 
      //loop if availableTicket >0    
         synchronized(pool) {
            if (neverBrought == false) {
               try {
                  //wait for execution
               }catch(InterruptedException e){
           if (pool.getTicket()>0) {
              // place order: print out "Thread xx reserved ticket --- #n"
             System.out.println(Thread.currentThread().getName()+" reserved ticket # "+ pool.getTicket());
              //delay 10ms: sleep(10)
                catch (InterruptedException itro){
                 System.out.println("sleep is interrupted");
                //payment finished: decrease availableTicket by 1 
                //print the leftover tickets
                System.out.println(Thread.currentThread().getName()+" bought ticket # " + (pool.getTicket()+1) + ", ticket left: "+pool.getTicket());
               //notify execution
            }else {


      }// go back to buy another once (while loop)   

   }// end of override run()


class TicketPool {
   int availableTicket;
   TicketPool(int totalTicket)
      this.availableTicket = totalTicket;
   void setTicket(int newNumber)
      availableTicket = newNumber;
   int getTicket(){
      return availableTicket;

public class TicketDemo3{
   public static void main (String[] args){
      // start 4 threads from a object of class Ticket that implements the "Runnable" interface
      TicketPool tickets = new TicketPool(10);
      // start 4 threads from the same object
      Buyer3 t1 = new Buyer3(tickets);
      Buyer3 t2 = new Buyer3(tickets);
      Buyer3 t3 = new Buyer3(tickets);
      Buyer3 t4 = new Buyer3(tickets);

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