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.
But how do I solve this problem with concurrent Haskell?
Suppose thread A execute a query, and while this query is still active,
a thread B execute another query.
I should suspend thread B (calling yield), but how do I resume it when
the query executed by thread A completes?
The GHC concurrent Haskell does not have a function to resume a given
thread (as found, as an example, in Lua).
P.S.: another question.
Why, in ghci, every time I call myThreadId, I get a different value?
Prelude Control.Concurrent> myThreadId
ThreadId 40
Prelude Control.Concurrent> myThreadId
ThreadId 41
Thanks Manlio Perillo
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