How to terminate a recursive function after a specific time? - c++

Question

I have a recursive function in C++ and I need to immediately terminate the function including all calls which have recursively made after a specific time, say 60 secs.
I have tried the following but doesn't work. takesTooLong is a global variable but if its value changes to 1 in one call, other calls keep seeing it as 0.
The OS is Ubuntu 12.10.
main() is something like this:
int main()
{
takesTooLong = 0;
startTime = clock();
RecursiveFunction();
endTime = clock();
printf("Elapsed time: %f", CalculateElapsedTime(startTime, endTime));
return 0;
}
My recursive function:
void RecursiveFunction(Some Parameters)
{
if (takesTooLong == 1)
return;
endTime = clock();
differenceTime = CalculateElapsedTime(startTime, endTime);
if (differenceTime > MAX_SECONDS)
{
takesTooLong = 1;
}
if (takesTooLong == 0)
{
for (i = 0; i < n && takesTooLong == 0; i++)
{
RecursiveFunction(Some Updated Parameters);
}
}
}

Answer 1

Pseudocode:
typedef ??? Time;//time type
Time getCurrentTime(); //returns time. Or ticks. Anything you could use to measure time.
void recursiveFunction(Time startTime){
...//do something here
Time currentTime = getCurrentTime();
if ((currentTime - startTime) > limit)
return;
recursiveFunction(startTime);
}
void recursiveFunction(){
Time startTime = getCurrentTime();
recursiveFunction(startTime);
}

Answer 2

Yes, you still have to unroll the stack but the alternatives are all ugly, the best probably being longjmp. If you need greater resolution than seconds, or you want to measure process/kernel time rather than wall clock time, use alternatives like timer_create or setitimer.
void alarmHandler (int sig)
{
timedOut = 1;
}
signal(SIGALRM, alarmHandler);
alarm(60);
RecursiveFunction();
alarm(0);
if (timedOut)
{
//report something
timedOut = 0;
}
void RecursiveFunction(Some Parameters)
{
if (timedOut)
return;
//........
}

Answer 3

The easiest way to exit an unknown number of recursions is by throwing an exception. Since you're doing it at most once every 60 seconds, this isn't too bad. Just make it a class TimeLimitExceeded : public std::runtime_error and catch that in the top level wrapper†.
† Most recursive functions should not be called directly, but via a non-recursive wrapper. The signature of the recursive function usually is inconvenient for callers, as it contains implementation details that are irrelevant to the caller.