[Haskell-cafe] Re: catting to cat gets stuck at > 135K

Brandon S. Allbery KF8NH allbery at ece.cmu.edu
Thu Nov 27 11:38:35 EST 2008

On 2008 Nov 27, at 8:51, Simon Marlow wrote:
> Brandon S. Allbery KF8NH wrote:
>> On 2008 Nov 10, at 19:04, Jason Dusek wrote:
>>>>> simple exe bytes args        =  do
>>>>> (i, o, e, p)            <-  runInteractiveProcess exe args Nothing
>>>>> Nothing
>>>>> hPut i bytes
>>>>> s                       <-  hGetContents o
>>>>> hClose i
>>>>> return s
>>>> Yep, that's your problem.  forkIO the hPut.
>>> Maybe I didn't do enough here -- just wrapping in `forkIO`
>>> does not seem to actually help.
>> *sigh* I hate the ghc runtime... it works in ghci, or compiled with  
>> -threaded.
> Would you hate it less if -threaded were the default?
>> Otherwise you still get the deadlock because it only switches  
>> threads under limited circumstances (garbage collections?)
> No, the issue is that without real OS threads, a foreign call can't  
> be pre-empted (pretty obvious when you think about it).   
> waitForProcess ends up making a blocking foreign call - non-obvious,  
> but at least it's documented.

The way this is usually handled in the non-threaded case is to either  
use SIGCHLD or non-blocking waitpid() so that "green" threads can  
continue running.  I'm a little surprised this wasn't done.

brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH

More information about the Haskell-Cafe mailing list