[Haskell-cafe] Re: Hugsvs GHC (again)was: Re: Somerandomnewbiequestions

Simon Marlow simonmar at microsoft.com
Wed Jan 19 08:39:05 EST 2005

On 19 January 2005 09:45, Ben Rudiak-Gould wrote:

> Glynn Clements wrote:
>  >Ben Rudiak-Gould wrote:
>  >
>  >>GHC really needs non-blocking
>  >>I/O to support its thread model, and memory-mapped I/O always
>  blocks. >
>  >If, by "blocks", you mean that execution will be suspended until the
>  >data has been read from the device into the buffer cache, then Unix
>  >non-blocking I/O (i.e. O_NONBLOCK) also blocks.
> Okay, my ignorance of Posix is showing again. Is it currently the
> case, then, that every GHC thread will stop running while a disk read
> is in progress in any thread? Is this true on all platforms?

It's true on Unix-like systems, I believe.  Even with -threaded.  It
might not be true on Win32.

> (By the way, are the GHC folks aware that the description of Win32 I/O
> at [2] is wrong? It seems to assume that ReadFile doesn't return until
> the buffer is full.)

I don't think that description corresponds with the implementation, but
then I'm not terribly familiar with that part of the code.  It doesn't
get used when -threaded is on.


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