C#: Exceptions are slllooooowwwww

Exceptions, eh? I've always avoided them in high performace code, because everyone knows they're slow. I have never actually bothered testing this though, relying on cleverer and more dedicated people than me doing the grunt work.

Currently, I am writing a high throughput application that performs actions based on a passed in "verb".

Normally, I deal with this by setting up the verbs as an enum and using Enum.Parse() to return the verb and check it is valid at the same time.

I had no idea how quick Enum.Parse() actually is, so decided to test it.

The testing code uses the handy System.Diagnostics.Stopwatch class. It uses an enum containing 3 names, and creates a List<String> of 500,000 of each of those three values; so 1,500,000 strings in total.

The code the loops through the array and converts the strings to the enum values using either Enum.Parse() or hardcoded if / else constructs using String.Compare(String, String, StringComparison).

I also tossed a switch statement in there; usually I avoid them because I find the syntax ugly and opaque, but I read on an MS blog that switches on strings are converted to a hash comparison, so I though if that was true it may be worth checking for speed against the if / else. The switch used String.ToUpper() in the checking loop to provide case-insensitivity.

I then repeated the tests, but this time with every string an invalid enum value. Obviously with the Enum.Parse() this requires catching an exception, and with the other two just an extra condition, in all cases just setting a private member bool flag.

Here are the results:

DoTheEnumThing()

Enum.Parse
00:00:08.64

if/else
00:00:03.48

switch
00:00:02.53

DoTheEnumThingWithErrors()

Enum.Parse
00:05:15.11

if/else
00:00:05.63

switch
00:00:02.74

I think that pretty conclusively demonstrates that exception handling is slow. You certainly wouldn't want to use it in a high throughput situation where you were expecting a lot of invalid values to be passed. The switch is appreciably faster than the if / else, so this hardcoded solution, though ugly, is definitely the speediest way to go.