Concurrency issue with dynamic linker in GHC

[Simon Marlow]

Simon Marlow wrote:
> Bulat Ziganshin wrote:
> 
>> Hello Vyacheslav,
>>
>> Monday, October 23, 2006, 7:20:47 AM, you wrote:
>>
>>
>>> Bulat: I didn't get the chance to use the streams library yet, but
>>> could you explain how it would solve my locking problem? The core
>>> problem that the runtime under Win32 doesn't have an IO manager still
>>> remains, correct?
>>
>>
>>
>> i will say instead "ghc I/O library on windows doesn't include IO 
>> manager".
>>
>> there are 3 possible ways to implement I/O:
>>
>> 1) use read() calls marked as unsafe. it will block all haskell
>> threads while one thread do I/O
>>
>> 2) use calls marked as safe. your I/O becomes fine
>>
>> 3) implement I/O manager which will make special asyncRead() calls and
>> then wake up just the Haskell thread that completed its i/o. in terms
>> of functionality, it's the same as 2), but a MUCH faster when you have
>> a lot of I/O (imagine web server with thousands of threads running
>> simultaneously)
>>
>>
>> GHC i/o lib implements 3) on unixes but only 1) on windows. my Streams
>> lib implement 1) on any system. BUT...
> 
> 
> I beg to differ ;-)  On Windows:
> 
>   without -threaded
>     * reads are implemented by the RTS which provides non-blocking
>       I/O using OS threads.  (see win32/IOManager.c etc.)
> 
>   with -threaded
>     * reads are implemented with safe foreign calls, with no
>       special support from the RTS.
> 
> So you get non-blocking I/O in both cases on Windows.  The lack of an 
> I/O manager thread doesn't affect the non-blockiness of I/O on Windows.  
> It does affect the efficiency: each blocked I/O request on Windows has 
> an associated OS thread, which gets quite expensive when you have a few 
> of them.  It also affects signal handling (console events), which is 
> what #637 is about.
> 
>   http://hackage.haskell.org/trac/ghc/ticket/637

Oh, I forgot to mention.

Perhaps your bug is that you're using hGetBufNonBlocking, which isn't on Windows?

Cheers,
	Simon