Program Semaphores: Write Monitor Alarm Clock Delay Time Units

[prashantgolu]

Write a monitor that implements an alarm clock that enables a calling program to delay itself for a specifed number of time units (ticks). You may assume the existence of a real hardware clock that invokes a procedure "tick" in your monitor at regular intervals.

the solution is :

monitor AlarmClock

int now=0;
condition wakeup;


wakeme(int n){
int alarm;
alarm = now + n;
while (now < alarm) wakeup.wait(alarm);
wakeup.signal;
}


tick() {
now = now + 1;
wakeup.signal;
}

Why Wakeup.signal in wake me function...i think the last wakeup signal in tick() will wakeup the process...

 

[fadiaz97]

if there is another process that can be woke up at the same tick

 

[newjerseyrunner]

What library are you using and what language is that? It looks like C, but has some glaring syntax problems.

Sounds like you want a simple message handling system. You will need two threads to properly demonstrate it: one that's doing the waiting, and the one that's looping through ticks until it can trigger the callback.

 

[rcgldr]

The solution doesn't handle wrap around, and tick should use a separate signal. An example that does:

int now=0;
condition wakeup;
condition ticksleep;

wakeme(int n){
int alarm;
int then;
then = now;
while((now - then) < n) wakeup.wait(ticksleep);
wakeup.signal;
}

tick() {
now = now + 1;
ticksleep.signal;
}