Re: [Haskell-cafe] ANN: Monad.Reader Issue 19

2011-10-31 Thread Joey Adams 
On Wed, Oct 26, 2011 at 4:24 PM, Bas van Dijk v.dijk@gmail.com wrote:
 I have one question regarding your use of atomicModifyIORef:

  x - atomicModifyIORef ref (\_ - (tmstr, ()))
  x `seq` return ()

 Can't you write that as just: writeIORef ref tmstr? If you're not
 using the previous value of the IORef there's no chance of
 inconsistency.

From the documentation at
http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-IORef.html
:

IORef operations may appear out-of-order to another thread, ...

...

atomicModifyIORef acts as a barrier to reordering. Multiple
atomicModifyIORef operations occur in strict program order.

Based on this description, it seems that atomicModifyIORef is safer
for writing to an IORef than writeIORef when there are multiple
threads reading and writing it.  If my assessment is correct, I think
Data.IORef should have an atomicWriteIORef :: IORef a - a - IO ()
function to clarify this.  I'm not completely sure about this myself.
Could someone confirm this?

Moreover, it'd be nice if there were writeIORef' and
atomicModifyIORef' functions that force the value.  Doing so would
help people avoid making the mistake described by the author.  It's a
really common mistake.

- Joey

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] ANN: Monad.Reader Issue 19

2011-10-30 Thread Iustin Pop 
On Wed, Oct 26, 2011 at 03:17:47PM -0400, Brent Yorgey wrote:
 I am pleased to announce that Issue 19 of The Monad.Reader, a special
 issue on parallelism and concurrency, is now available:
 
   http://themonadreader.files.wordpress.com/2011/10/issue19.pdf

Thanks a lot for the TMR, it's a pleasure to read, as always.

If like me there are people who (would like to) read this on an ebook
reader, these are the changes that finally give me good results on a
Sony Reader:

\usepackage[papersize={90mm,120mm},margin=2mm]{geometry}
\usepackage[kerning=true]{microtype}
\usepackage[T1]{fontenc}
\usepackage[charter]{mathdesign}
\usepackage{hyperref}
\hypersetup{pdftitle={The Monad Reader 19}}
\sloppy

Additionally, all the \includegraphics commands need changing from
absolute measurements (e.g. width=6cm) to something relative; in my
case, I just used \textwidth. And finally, the verbatim sections need a
bit smaller font, as they can't be reflowed nicely; or alternatively,
inserting manual line wraps (keeping the code consistent).

regards,
iustin

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] ANN: Monad.Reader Issue 19

2011-10-26 Thread Brent Yorgey 
I am pleased to announce that Issue 19 of The Monad.Reader, a special
issue on parallelism and concurrency, is now available:

  http://themonadreader.files.wordpress.com/2011/10/issue19.pdf

Issue 19 consists of the following three articles:

  * Mighttpd – a High Performance Web Server in Haskell 
by Kazu Yamamoto 

  * High Performance Haskell with MPI 
by Bernie Pope and Dmitry Astapov

  * Coroutine Pipelines 
by Mario Blažević

Feel free to browse the source files. You can check out the entire
repository using darcs:

  darcs get http://code.haskell.org/~byorgey/TMR/Issue19

If you’d like to write something for Issue 20, please get in
touch. The deadline will likely be in December; more details will be
forthcoming.

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: [Haskell-cafe] ANN: Monad.Reader Issue 19

2011-10-26 Thread Bas van Dijk 
On 26 October 2011 21:17, Brent Yorgey byor...@seas.upenn.edu wrote:
 I am pleased to announce that Issue 19 of The Monad.Reader, a special
 issue on parallelism and concurrency, is now available:

Thanks, I always really enjoy The Monad.Reader.

 Issue 19 consists of the following three articles:

  * Mighttpd – a High Performance Web Server in Haskell
    by Kazu Yamamoto

Kazu, really interesting article!

I have one question regarding your use of atomicModifyIORef:

  x - atomicModifyIORef ref (\_ - (tmstr, ()))
  x `seq` return ()

Can't you write that as just: writeIORef ref tmstr? If you're not
using the previous value of the IORef there's no chance of
inconsistency.

I looked in the git repository of mighttpd2 and it seems that in the
FileCache module we can make a similar change by rewriting:

remover :: IORef Cache - IO ()
remover ref = do
threadDelay 1000
_ - atomicModifyIORef ref (\_ - (M.empty, ()))
remover ref

to:

remover :: IORef Cache - IO ()
remover ref = forever $ do
threadDelay 1000
writeIORef ref M.empty

Regards,

Bas

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe