Question

A snooker club can be used by players of both sex i.e. male and female, but not both at the same time. If a boy is in the club, other boys may enter, but any girl wishing to play snooker should wait until all boys leave and club become empty. Similarly, if a girl is in the club, other girls may enter, but any boy wishing to play should wait till the club becomes empty. Implement a solution to this problem using SEMAPHORES. At maximum only 6 boys or 6 girls can enter the club and play snooker as there are only 3 tables available in the club.

Answer 1

Male Snooker:

do{
      
        // Male snooker want to enter into club so wait on m_snook
        // bcoz we are changing common variable n_m_snook(no of male snooker)
        wait(m_snook);
      
        //incrementing no of male snookers
        n_m_snook++;
      
        //blocking the female snookers if he is the first male snooker to enter into club
        if(n_m_snook==1)
        {
            wait(f_snook);
        }
      
      
        //blocking the male snooker if n_m_snook>6
        //since we can allow only 6 snookers
        if(n_m_snook>6)
        {
            //blocking male snooker until one male snooker left the club
           while(n_m_snook>6)
           {
               wait(m_snook);
           }
        }
      
        //now the male snooker entered into club
        //now we can allow other male snookers
        //so signal on m_snoock
        signal(m_snook);
      
        //one male snooker want to leave the club and change the n_m_snook
        //Therefore wait on m_snook
        wait(m_snook);
      
        //decrement the n_m_snook value
        n_m_snook--;
      
        //if he is the last male snooker to leave the club
        //then we can allow female snookers to the club
        if(n_m_snook==0)
        {
            signal(f_snook);
        }
      
        //male snooker changed n_m_snook value and left
        signal(m_snook);
      
      
    }while(true);

Female Snooker:

do{
      
        // female snooker want to enter into club so wait on f_snook
        // bcoz we are changing common variable n_f_snook(no of male snooker)
        wait(f_snook);
      
        //incrementing no of female snookers
        n_f_snook++;
      
        //blocking the male snookers if she is the first female snooker to enter into club
        if(n_f_snook==1)
        {
            wait(m_snook);
        }
      
      
        //blocking the female snooker if n_f_snook>6
        //since we can allow only 6 snookers
        if(n_f_snook>6)
        {
            //blocking female snooker until one female snooker left the club
           while(n_f_snook>6)
           {
               wait(f_snook);
           }
        }
      
        //now the female snooker entered into club
        //now we can allow other female snookers
        //so signal on f_snoock
        signal(f_snook);
      
        //one female snooker want to leave the club and change the n_f_snook
        //Therefore wait on f_snook
        wait(f_snook);
      
        //decrement the n_f_snook value
        n_f_snook--;
      
        //if she is the last female snooker to leave the club
        //then we can allow male snookers to the club
        if(n_f_snook==0)
        {
            signal(m_snook);
        }
      
        //female snooker changed n_f_snook value and left
        signal(f_snook);
      
      
    }while(true);

semaphores used: m_snook, f_snook

common variables used: n_m_snook, n_f_snook

wait()--decrements the value by 1(makes 0 )

signal()--increments the value by 1