Flush logs only in log write thread

Also add some traces to see whether this is actually executed.

hydra-node/src/Hydra/Logging.hs

@@ -49,6 +49,7 @@ import Data.Aeson (pairs, (.=))
 import qualified Data.Aeson as Aeson
 import qualified Data.ByteString.Lazy as LBS
 import qualified Data.Text as Text
+import Debug.Trace (traceIO)
 import Test.QuickCheck.Instances.Text ()
 import Test.QuickCheck.Instances.Time ()
 
@@ -105,7 +106,7 @@ withTracerOutputTo ::
 withTracerOutputTo hdl namespace action = do
   msgQueue <- newTBQueueIO @_ @(Envelope msg) defaultQueueSize
   withAsync (writeLogs msgQueue `finally` flushLogs msgQueue) $ \_ ->
-    action (tracer msgQueue) `finally` flushLogs msgQueue
+    action (tracer msgQueue)
  where
   tracer queue =
     Tracer $
@@ -117,9 +118,11 @@ withTracerOutputTo hdl namespace action = do
       hFlush hdl
 
   flushLogs queue = liftIO $ do
+    traceIO "flushLogs start"
     entries <- atomically $ flushTBQueue queue
     forM_ entries (write . Aeson.encode)
     hFlush hdl
+    traceIO "flushLogs end"
 
   write bs = LBS.hPut hdl (bs <> "\n")