[Haskell-cafe] ANN: Salvia-1.0.0

[Sebastiaan Visser]

Nice! This is certainly worth it. 

I really liked the simplicity of the threadmanager package, it certainly was better than managing threads manually. But your concurrent-extra package seems to do a way better job, I'm certainly going to apply this patch.

Thanks a lot guys!

Groet,
Sebastiaan

On Mar 23, 2010, at 12:36 PM, Bas van Dijk wrote:
> On Sun, Mar 21, 2010 at 5:05 PM, Sebastiaan Visser <sfvisser at cs.uu.nl> wrote:
>> Straight from Zurihac: I'm very pleased to announce the 1.0.0 release of the Salvia web server.
> 
> Hoi Sebastiaan,
> 
> (switching to English) I discovered a major space-leak in
> Network.Salvia.Impl.Server.start due to the use of threadmanager:
> 
> When a request handler is forked the threadmanager internally maps the
> threadId to a status MVar. However when the request handler terminates
> this association is not deleted from the internal Map. This results in
> a major O(n) space-leak where n = the number of requests accepted.
> 
> This space-leak can be visualized when you heap-profile the
> salvia-helloworld demo:
> 
> salvia-helloworld +RTS -hy
> 
> and perform some requests:
> 
> $ for ((a=0; a<10000; a++)); do curl -s -o /dev/null localhost:8080; done
> 
> You will then get the following heap profile which will clearly
> highlight the linear space-leak:
> 
> http://bifunctor.homelinux.net/~bas/salvia-helloworld_ORIGINAL_10000_requests.ps
> 
> I fixed it by replacing threadmanager by Control.Concurrent.Thread[1]
> from Roel's and mines concurrent-extra. This module has the following
> advantages over threadmanager:
> 
> * Simpler: We don't have the concept of a ThreadManager. So you don't
> need to make one and pass it to fork and wait.
> 
> * More efficient: We don't keep an internal mapping from ThreadIds to
> status MVars.
> 
> * Correct: threadmanager has a bug where it can potentially miss the
> termination of a thread. It doesn't block asynchronous exceptions
> before it forks the computation that will install the necessary
> exception handler before executing the given action. We correctly
> block asynchronous exceptions.
> 
> Besides these advantages we have the ability to get the return value
> of the forked thread so you don't need a mutable variable.
> 
> Besides replacing threadmanager I now manually delete the threadId of
> the request handler when it terminates.
> 
> When I repeat the heap-profile you will now see a nice constant heap-usage:
> 
> http://bifunctor.homelinux.net/~bas/salvia-helloworld_NEW_10000_requests.ps
> 
> I don't know how to attach my git patch to this email so I just copied
> my git repository to:
> 
> http://bifunctor.homelinux.net/~bas/salvia/
> 
> I think you can just pull from there.
> 
> Groeten,
> 
> Bas
> 
> [1] http://hackage.haskell.org/packages/archive/concurrent-extra/0.4/doc/html/Control-Concurrent-Thread.html