forced evaluation of logging message before blocking

app/Environment.hs

@@ -18,6 +18,7 @@ import System.IO.Unsafe(unsafePerformIO)
 import qualified Control.Concurrent.MVar as M
 import qualified Data.Text as T
 import qualified Data.Text.IO as T
+import Control.Parallel(pseq)
 
 newtype Env m = Env {logAction :: LogAction m Message}
 
@@ -54,7 +55,7 @@ syncMVar = unsafePerformIO $ newMVar ()
 {-# NOINLINE syncMVar #-}
 
 myLogAction :: LogAction EnvM Message
-myLogAction = LogAction $ \x -> EnvM . lift $ modifyMVar_ syncMVar (const (T.putStrLn . formatMessage $ x))
+myLogAction = LogAction $ \x -> let m = formatMessage x in EnvM . lift $ m `pseq` modifyMVar_ syncMVar (const (T.putStrLn m))
 
 formatMessage :: Message -> T.Text
 formatMessage Msg{..} =

package.yaml

@@ -49,6 +49,8 @@ dependencies:
 - unliftio-core
 - unliftio
 - mtl
+# for pseq in logging
+- parallel
 
 when:
   - condition: flag(http)

tickLeisteServer.cabal

@@ -56,6 +56,7 @@ executable tickLeisteServer
     , http-types
     , mtl
     , optparse-applicative
+    , parallel
     , text
     , tickLeiste
     , tickLeiste-aeson
@@ -97,6 +98,7 @@ test-suite tickLeisteServer-test
     , http-types
     , mtl
     , optparse-applicative
+    , parallel
     , text
     , tickLeiste
     , tickLeiste-aeson