Question

How expensive are exceptions in C#? It seems like they are not incredibly expensive as long as the stack is not deep; however I have read conflicting reports.

Is there definitive report that hasn't been rebutted?

Answer 1

Having read that exceptions are costly in terms of performance I threw together a simple measurement program, very similar to the one Jon Skeet published years ago. I mention this here mainly to provide updated numbers.

It took the program below 29914 milliseconds to process one million exceptions, which amounts to 33 exceptions per millisecond. That is fast enough to make exceptions a viable alternative to return codes for most situations.

Please note, though, that with return codes instead of exceptions the same program runs less than one millisecond, which means exceptions are at least 30,000 times slower than return codes. As stressed by Rico Mariani these numbers are also minimum numbers. In practice, throwing and catching an exception will take more time.

Measured on a laptop with Intel Core2 Duo T8100 @ 2,1 GHz with .NET 4.0 in release build not run under debugger (which would make it way slower).

This is my test code:

static void Main(string[] args)
{
    int iterations = 1000000;
    Console.WriteLine("Starting " + iterations.ToString() + " iterations...
");

    var stopwatch = new Stopwatch();

    // Test exceptions
    stopwatch.Reset();
    stopwatch.Start();
    for (int i = 1; i <= iterations; i++)
    {
        try
        {
            TestExceptions();
        }
        catch (Exception)
        {
            // Do nothing
        }
    }
    stopwatch.Stop();
    Console.WriteLine("Exceptions: " + stopwatch.ElapsedMilliseconds.ToString() + " ms");

    // Test return codes
    stopwatch.Reset();
    stopwatch.Start();
    int retcode;
    for (int i = 1; i <= iterations; i++)
    {
        retcode = TestReturnCodes();
        if (retcode == 1)
        {
            // Do nothing
        }
    }
    stopwatch.Stop();
    Console.WriteLine("Return codes: " + stopwatch.ElapsedMilliseconds.ToString() + " ms");

    Console.WriteLine("
Finished.");
    Console.ReadKey();
}

static void TestExceptions()
{
    throw new Exception("Failed");
}

static int TestReturnCodes()
{
    return 1;
}