bankteller.cpp

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//: C20:BankTeller.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Using a queue and simulated multithreading
// To model a bank teller system
#include <iostream>
#include <queue>
#include <list>
#include <cstdlib>
#include <ctime>
using namespace std;

class Customer {
  int serviceTime;
public:
  Customer() : serviceTime(0) {}
  Customer(int tm) : serviceTime(tm) {}
  int getTime() { return serviceTime; }
  void setTime(int newtime) {
    serviceTime = newtime;
  }
  friend ostream& 
  operator<<(ostream& os, const Customer& c) {
    return os << '[' << c.serviceTime << ']';
  }
};

class Teller {
  queue<Customer>& customers;
  Customer current;
  static const int slice = 5;
  int ttime; // Time left in slice
  bool busy; // Is teller serving a customer?
public:
  Teller(queue<Customer>& cq) 
    : customers(cq), ttime(0), busy(false) {}
  Teller& operator=(const Teller& rv) {
    customers = rv.customers;
    current = rv.current;
    ttime = rv.ttime;
    busy = rv.busy;
    return *this;
  }
  bool isBusy() { return busy; }
  void run(bool recursion = false) {
    if(!recursion)
      ttime = slice;
    int servtime = current.getTime();
    if(servtime > ttime) {
      servtime -= ttime;
      current.setTime(servtime);
      busy = true; // Still working on current
      return;
    }
    if(servtime < ttime) {
      ttime -= servtime;
      if(!customers.empty()) {
        current = customers.front();
        customers.pop(); // Remove it
        busy = true;
        run(true); // Recurse
      }
      return;
    }
    if(servtime == ttime) {
      // Done with current, set to empty:
      current = Customer(0);
      busy = false;
      return; // No more time in this slice
    }
  }
};

// Inherit to access protected implementation:
class CustomerQ : public queue<Customer> {
public:
  friend ostream& 
  operator<<(ostream& os, const CustomerQ& cd) {
    copy(cd.c.begin(), cd.c.end(), 
      ostream_iterator<Customer>(os, ""));
    return os;
  }
};

int main() {
  CustomerQ customers;
  list<Teller> tellers;
  typedef list<Teller>::iterator TellIt;
  tellers.push_back(Teller(customers));
  srand(time(0)); // Seed random number generator
  while(true) {
    // Add a random number of customers to the
    // queue, with random service times:
    for(int i = 0; i < rand() % 5; i++)
      customers.push(Customer(rand() % 15 + 1));
    cout << '{' << tellers.size() << '}' 
      << customers << endl;
    // Have the tellers service the queue:
    for(TellIt i = tellers.begin(); 
      i != tellers.end(); i++)
      (*i).run();
    cout << '{' << tellers.size() << '}' 
      << customers << endl;
    // If line is too long, add another teller:
    if(customers.size() / tellers.size() > 2)
      tellers.push_back(Teller(customers));
    // If line is short enough, remove a teller:
    if(tellers.size() > 1 && 
      customers.size() / tellers.size() < 2)
      for(TellIt i = tellers.begin();
        i != tellers.end(); i++)
        if(!(*i).isBusy()) {
          tellers.erase(i);
          break; // Out of for loop
        }
  }
} ///:~