Exception from Random.Next() crashes program within a try-catch block

Question

So, this happened:

How is this possible within a try-block? How come it does not forward that to the catch-block?

Edit:

It has been pointed out, that I might have recursion. I do, which I did not think would cause a problem.

The full method looks like this:

private static GeoCoordinate ChangeLocation(GeoCoordinate location)
{
    var tmp = location;
    var direction = new Random().Next(0, 359);
    var distance = new Random().Next(0, 5);

    //Calculate movement
    var vertical = Math.Sin(direction) * distance; //Sinus relation shortened
    var lastAngle = 180 - 90 - (direction % 90);
    var horisontal = Math.Sin(lastAngle) * distance; //Sinus relation shortened

    //Add movement to location
    tmp.Latitude = location.Latitude + (vertical / 10000);
    tmp.Longitude = location.Longitude + (horisontal / 10000);

    //If new location is outside a specific area
    if (!InsidePolygon(_siteCoordinates, tmp))
    {
        _recursiveCounter++;
        //Ninja edit: @Leppie pointed out I was missing 'tmp =':
        tmp = ChangeLocation(location); //Recursive move to calculate a new location
    }

    //Print the amount of recursive moves
    if (_recursiveCounter != 0)
        Console.WriteLine($"Counter: {_recursiveCounter}");
    _recursiveCounter = 0;

    return tmp;
}

Answer 1

Starting with 2.0 a StackOverflow Exception can only be caught in the following circumstances.

1. The CLR is being run in a hosted environment where the host specifically allows for StackOverflow exceptions to be handled
2. The stackoverflow exception is thrown by user code and not due to an actual stack overflow situation (Reference)

https://stackoverflow.com/a/1599238/4136669

MSDM

Answer 2

The problem

You have a stack overflow-exception. This happens when the all stack memory is used. This mostly happens when you have a recursive loop. So method A calls method B, which calls method C, which calls method A, calling method B, calling method C, etc. etc. etc.

Somewhere in this loop, the stack overflows and results in this exception. The place of the exception is not important. In your case it is Random.Next(), but it could also have happened in Console.WriteLine or anywhere else.

The StackOverflowException is a special type of exception which cannot always be cought by a try-catch.

In short: It has nothting to do with Random.Next() or try-catch. Just try to find and fix the recursive loop.

How to solve find a recursive loop

• Set a breakpoint somewhere in your breaking code.
• Run your application untill the breakpoints hits.
• Continue till the breakpoinnt hits again. Repeat this 3 or 4 times.
• Now analyze your stack trace and find out where your recursive loops starts (which methods are beging repeated) and fix the recursion.

Answer 3

Okay - there has been a lot of good suggestions. Here's a break down what is actually wrong:

• I called a recursive function, which somehow made the code crash.
• I did not use the return value from ChangeLocation() in my recursive call (thanks @leppie).
• The _recursiveCounter had a value +3000, which means this just keeps repeating it self.
• Random() can have a seed to generate a new start-value. Because the code runs so fast, it's the same number popping out all the time, resulting in the same value for both direction and distance. Adding a seed value (with a Sleep, as Microsoft points out) could be a solution, or just a new seed value.
• But this can be done a tat smarter, since I have the _recursiveCounter.

The root cause is the Random().Next(...) being called too many times cause something else to throw the exception.

var direction = new Random(DateTime.Now.Millisecond + _recursiveCounter).Next(0, 359);
var distance = new Random(DateTime.Now.Millisecond + _recursiveCounter).Next(0, 5);