Re: [Haskell-cafe] Space leak with recursion

24 Apr 2015

      ...
...
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