Question

Could your please help me with following interview question.

Given function ‪Sleep(int seconds) implement following interface so timers could be used:

• function ‪void CreateTimer(void (*func)(), int seconds) that her purpose is to create timer
• function ‫‪void StartTimers() that her purpose to start all the timers

Every timer that started should delay for several seconds and then use a callback to call a function.
Example:

CreateTimer(func1,3);
CreateTimer(func2,7);
CreateTimer(func3,10);
StartTimers()

The folowing should be happening:

Delay for 3 seconds and then call for function 1.
Delay for 4 seconds and then call for function 2.
Delay for 3 seconds and then call for function 3.

The question is how implement such interface?

Answer 1

EDIT 1: Use the questions API.

EDIT 2: Oops, didn’t call q.pop();

This sounds like a job for std::priority_queue, ordered by deadline.

//pseudo-code
class Job;
std::priority_queue<Job, std::vector<Job>, CompareLessByDeadline> q;

CreateTimer(func, deadline) {
   q.push(Job(func, deadline));
}
StartTimers() {
  now = 0;
  while(!q.empty()) {
    Job& j = q.top();
    Sleep(j.deadline-now);
    now = j.deadline;
    j.function();
    q.pop();
  }
}