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

On Wed, Jan 12, 2005 at 12:21:25AM +0000, Aaron Denney wrote:

On 2005-01-11, Simon Marlow wrote:

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On 11 January 2005 14:15, Gracjan Polak wrote:

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Simon Marlow wrote:

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There's a big lock on File. If you want to do truly concurrent reading, > you can make multiple FileInputStreams, each of which has its own file > descriptor (the Unix implementation uses dup(2)).

Original and descriptor returned by dup or dup2 share file pointer.

*blink*

You're right! Serves me right for assuming that POSIX would have sensible semantics. Perhaps this API isn't implementable, in its current state.

Others have pointed out pread() and pwrite(); Perhaps we can stick this function in an extension package. (Though it is required for Unix 98 conformance, so anything reasonable will have it. Hmm. Does open("/dev/fd/n") or ("/proc/self/fd/n") act as dup() or a fresh open() to underlying file?)

Actually, If I were writing new haskell libraries, I would use mmap whenever I could for accessing files. not only does it make the file pointer problem go away, but it can be drastically more efficient. of course, this can only be done on a limited type of file on some architectures, so it should be an optimization under the hood rather than an exposed interface. John -- John Meacham - ⑆repetae.net⑆john⑈