Proposal: Retrieving the System Event Manager

When you want to use the system event manager (the one started by the RTS) you currently have to do something like this:

{-# LANGUAGE ForeignFunctionInterface #-}

import System.Event (EventManager)
import GHC.Conc.Sync (sharedCAF)
import Foreign.Ptr (Ptr)
import Data.IORef (IORef, newIORef, readIORef)
import System.IO.Unsafe (unsafePerformIO)

main = do
  Just mgr <- readIORef eventManager
  ...

eventManager :: IORef (Maybe EventManager)
eventManager = unsafePerformIO $ do
    em <- newIORef Nothing
    sharedCAF em getOrSetSystemEventThreadEventManagerStore
{-# NOINLINE eventManager #-}

foreign import ccall unsafe "getOrSetSystemEventThreadEventManagerStore"
    getOrSetSystemEventThreadEventManagerStore :: Ptr a -> IO (Ptr a)

I propose to abstract this ugliness in a function:

getSystemEventManager :: IO (Maybe EventManager)
getSystemEventManager = readIORef eventManager

and export it from GHC.Event.

I don't think this needs to go through the library submission process since the module is GHC specific.

See the thread on the libraries list.

Trac metadata

Trac field	Value
Version	7.0.3
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
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