A monitor is to be written to simulate a clock manager used for real-time contro
ID: 3695384 • Letter: A
Question
A monitor is to be written to simulate a clock manager used for real-time control of concurrent processes. The clockmanager uses a variable named clock to maintain the current time. The OS supports a signal called elapsed_time that is generated every 2 ms. The clock manager provides a signal handling action for elapsed_time that updates clock at every occurrence of the signal. This action is coded as a procedure of the monitor. A typical request made to the clock manager is “wake me up at 9.00 a.m.” The clock manager blocks the processes making such requests and arranges to activate them at the designated times. Implement this monitor.
Explanation / Answer
public class AlarmClock { // these are instance variables - each alarm clock has its // own copy of these variables // current time private int currentHour; private int currentMinute; private int currentSecond; // time of the alarm(s) private int[] alarmHour; private int[] alarmMinute; // whether alarm is on or off private boolean[] alarmOn; // this is the constructor - this is called when "new" // is called, when the object is first created // this contains code to initialize all variables in object // this is a special method - it has no return value (and no void) public AlarmClock() { currentHour = currentMinute = currentSecond = alarmHour = new int[2]; alarmMinute = new int[2]; alarmOn = new boolean[2]; // set both alarms to off } // now we put all of the methods // each method that we want code from outside the class to call is public // each method that we only want code from inside the class to call is private /* setAlarm * inputs: alarm number, hour, minute * outputs: none * purpose: sets one of the alarms to the hour and minute specified * It also turns on the alarm */ public void setAlarm(int alarm, int hour, int minute) { // make sure the alarm number is valid // set that alarm // turn on alarm } /* turnOffAlarm * inputs: the alarm number * outputs: none * purpose: This turns off an alarm. */ public void turnOffAlarm(int alarm) { // make sure the alarm number is valid // turn off alarm } /* turnOnAlarm * inputs: the alarm number * outputs: none * purpose: This turns on an alarm. This assumes the alarm time has * already been set. */ public void turnOnAlarm(int alarm) { // make sure the alarm number is valid // turn on alarm } /* setTime * inputs: hour, minute, second * outputs: none * purpose: This updates the current time to the values * passed in. */ public void setTime(int hour, int minute, int second) { currentHour = hour; currentMinute = minute; currentSecond = second; } /* tick * inputs: none * outputs: none * purpose: This gets called each second. It updates the current time * of the clock and sets of the alarm if necessary */ public void tick() { // print out tick, then tock, then tick, etc. if (seconds % 2 == 0) System.out.println("Tick"); else System.out.println("Tock"); // increment the time // check to see if an alarm should go off } /* soundAlarm * inputs: none * outputs: none * purpose: this gets called by tick when the alarm goes off * It sounds an alarm */ private void soundAlarm() { System.out.println("Alarm!!**************************"); } } // end of class AlarmClock