[Haskell-cafe] Space leak with recursion

[Martijn Rijkeboer]

>> Once thee space leak is fixed I will need to add code to increment the
>> sequence number (not yet implemented).
>
> In that case the most important thing to do is to try to reproduce the
> space leak without the snapshot socket.

I've just ran the code below (removed the snapshot socket) and the
space leak is still there. Since I don't have access to a Windows
box at the moment this was tested on the following configuration:
- OS: Ubuntu 14.04 (64-bit)
- GHC: 7.8.4 (64-bit)
- Zeromq4-haskell: 0.6.3  (Stackage LTS 2.4)
- ZeroMQ: 4.0.4 (64-bit)


> Very sensible.  I was confused for a moment whether the minimal version
> did actually exhibit the space leak behaviour.
>
> To get the state-updating behaviour you want, I suggest you use
> `StateT IO` rather than `IO`.  With handlers in the `StateT IO` monad
> the state updates will occur as you expect.

Thanks for the suggestion I'll try that, but it will take me some time.

Kind regards,


Martijn Rijkeboer


--- code ---

module Observable
    ( run
    ) where

import Control.Monad (void)
import Data.Int (Int64)
import System.ZMQ4


data State = State
    { nextSeqNum    :: !Int64
    , listenSocket  :: !(Socket Pull)
    }


run :: IO ()
run = do
    withContext $ \ctx ->
        withSocket ctx Pull $ \observer -> do
            setLinger (restrict (0::Int)) observer
            bind observer "tcp://*:7010"

            let state = State
                    { nextSeqNum = 0
                    , listenSocket = observer
                    }

            pollSockets state


pollSockets :: State -> IO ()
pollSockets state =
    void $ poll (-1) [ Sock (listenSocket state) [In] (Just $
observerHandleEvts state) ]


observerHandleEvts :: State -> [Event] -> IO ()
observerHandleEvts state _ = do
    void $ receiveMulti $ listenSocket state
    -- TODO: update state by incrementing the nextSeqNum
    pollSockets state