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

On Wed, Feb 2, 2011 at 10:15 PM, Felipe Almeida Lessa wrote:

On Wed, Feb 2, 2011 at 11:57 AM, Michael Snoyman 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

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

B)  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.

Good point: it should be a MVar (Map HostInfo (MVar Socket)) I think* Thanks, Michael * It's late here, just make sure I'm not saying something stupid ;).