Re: [Caml-list] Performance penalty of exception handling

[John Whitington <john@coherentgraphics.co.uk>]

Hi,

Helmut Brandl wrote:
> I use exeption handling quite frequently even in inner loops. A common
> pattern:
>
> let some_function ... =
> ...
> if cannot_compute then raise Not_found else value
>
> try
> let value = some_function ... in
> ...
> with Not_found ->
> handle_exception
>
> I use this pattern even if the direct caller of "some_function" handles
> the exception. In many cases I could design "some_function" in a way
> that it returns an optional value and check the optional value in the
> caller. Is this significantly (at least 10%) faster?

Optional values often require allocation (and, therefore, garbage 
collection). Unless your process is so short-lived that the garbage 
collector never runs, exceptions are going to be faster. So, if you 
benchmark this, make sure your benchmarks run for a while.

Someone who knows the compiler better than I will be able to tell you if 
(Some x) when immediately pattern-matched across a function call causes 
an allocation.

Constant exception constructors like Not_found, I believe, require no 
allocation in recent versions of OCaml.

Cheers,

-- 
John Whitington
Director, Coherent Graphics Ltd
http://www.coherentpdf.com/