manlio_perillo:
Hi.
I have a question about concurrent Haskell in GHC.
Suppose I want to write a native pure Haskell PostgreSQL client. I have done this for Python (using Twisted): http://hg.mperillo.ath.cx/twisted/pglib/
and I would like to do this in Haskell, as an exercise.
The main problem is with multiple concurrent queries to the same connection, from multiple threads.
PostgreSQL supports multiple requests but it's better to execute only one request at a time: http://www.postgresql.org/docs/8.3/interactive/protocol-flow.html#AEN73647
In the Twisted version I queue all the requests, and every time a request completes I call the callback associated with the request and execute the next available request.
I'd queue or sychronise all threads requesting the underlying non-thread safe resource by using either STM transactions, or an MVar. -- Don