[Haskell-beginners] filesystem verification utility

[Stephen Tetley]

Hi Anand

Firstly apologies - my advice from yesterday was trivial advice,
changing to a better representation of Strings and avoiding costly
operations (++) is valuable and should improve the performance of the
program, but it might be a small overall improvement and it doesn't
get to the heart of things.

Really you need to do two things - one is consider what you are doing
and evaluate whether it is appropriate for a performance sensitive
app, the other is to profile and find the bits that are too slow.

I rarely use Control.Concurrent so I can't offer any real experience
but I'm concerned that it is adding overhead for no benefit. Looking
at the code and what the comments say it does - I don't think your
situation benefits from concurrency. A thread in your program could do
all is work in one go, its not that you need to be servicing many
clients (cf. a web server that needs to service many clients without
individual long waits so it makes sense to schedule them) or that you
are waiting on other processes making resources available. So for your
program, any changes to execution caused by scheduling / de-scheduling
threads (probably) just add to the total time.

If you have a multi-core machine you could potentially benefit from
parallelism - splitting the work amongst available cores. But in GHC
forkIO spawns "green threads" which run in the same OS thread so you
won't be getting any automatic parallelism from the code even if you
have multi-core.

However don't take my word for this - I could easily be wrong. If you
want performance you really do need to see what the profiler tells
you.

Best wishes

Stephen