[Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive

Felipe Almeida Lessa felipe.lessa at gmail.com
Wed Feb 2 21:15:40 CET 2011

On Wed, Feb 2, 2011 at 11:57 AM, Michael Snoyman <michael at snoyman.com> wrote:
> As far as keep-alive goes, I still need to do a bit more research, but
> my basic idea (with credit to Bryan O'Sullivan):
> * http (and family) will all take an extra argument, Maybe Manager.
> * Manager will be an abstract type that will keep an MVar (Map (Host,
> Port, IsSecure) Socket).
> * If http is provided with a Manager, then it uses the Socket
> available in the Manager. If none is available, it creates a new
> Socket and places it in the Manager.
> * If http is *not* provided with a Manager, then it creates a new
> socket and closes it before returning.
> * There will be a newManager :: IO Manager, and a closeManager ::
> Manager -> IO (), which closes all Sockets in the Manager and empties
> out the inner Map.

How about concurrent use of Manager?  Should we do

  do m <- newManager
       forM xs $ forkIO $ doSomething m

  forM xs $ forkIO $ do
    m <- newManager
    doSomething m

While B) should work with any sane Manager implementation, it is not
optimal.  If all your connections are to the same host, than both
approaches are the same.  But if access hosts O and P, for example,
than it is possible that Manager m1 has an open connection to O, but
you try connect to O using another Manager m2.  That means that
ideally we should support approach A) as well.  However, to support A
a simple Map inside an MVar isn't sufficient.

Cheers! =)


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