not.hDuplicate

[Peter Simons]

Bulat Ziganshin writes:

 > one thread gives to another handle of open file. i need
 > to read some data from this file. how can i accomplish
 > this?

Keep the Handle in an MVar at all times, then access to it
will be synchronized between threads:

  http://haskell.org/ghc/docs/latest/html/libraries/base/Control.Concurrent.MVar.html

If you need more background on this stuff, this paper is the
one you want to read:

  http://research.microsoft.com/Users/simonpj/papers/marktoberdorf/

Peter