From b9a181870ce82c309613fba17edd9fd0b78b43cc Mon Sep 17 00:00:00 2001
From: Daniel Schüssler <933504+DanielSchuessler@users.noreply.github.com>
Date: Sun, 26 Aug 2018 22:40:27 +0200
Subject: Signal termination to plugin threads and wait for them upon program
 exit

This is necessary to allow the plugin threads to run their cleanup actions.
---
 src/Main.hs   | 22 ++++++++++++++++------
 src/Xmobar.hs | 17 +++++++++--------
 xmobar.cabal  |  3 ++-
 3 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/src/Main.hs b/src/Main.hs
index 4f35b38..9a3a2e8 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -25,6 +25,7 @@ import Parsers
 import Config
 import XUtil
 
+import Data.Foldable (for_)
 import Data.List (intercalate)
 import qualified Data.Map as Map
 
@@ -37,6 +38,8 @@ import System.Exit
 import System.Environment
 import System.FilePath ((</>))
 import System.Posix.Files
+import Control.Exception
+import Control.Concurrent.Async (Async, cancel)
 import Control.Monad (unless)
 import Text.Read (readMaybe)
 
@@ -63,12 +66,19 @@ main = do
   fl    <- mapM (initFont d) (additionalFonts conf)
   cls   <- mapM (parseTemplate conf) (splitTemplate conf)
   sig   <- setupSignalHandler
-  vars  <- mapM (mapM $ startCommand sig) cls
-  (r,w) <- createWin d fs conf
-  let ic = Map.empty
-      to = textOffset conf
-      ts = textOffsets conf ++ replicate (length fl) (-1)
-  startLoop (XConf d r w (fs:fl) (to:ts) ic conf) sig vars
+  bracket (mapM (mapM $ startCommand sig) cls)
+          cleanupThreads
+          $ \vars -> do
+    (r,w) <- createWin d fs conf
+    let ic = Map.empty
+        to = textOffset conf
+        ts = textOffsets conf ++ replicate (length fl) (-1)
+    startLoop (XConf d r w (fs:fl) (to:ts) ic conf) sig vars
+
+cleanupThreads :: [[([Async ()], a)]] -> IO ()
+cleanupThreads vars =
+  for_ (concat vars) $ \(asyncs, _) ->
+    for_ asyncs cancel
 
 -- | Splits the template in its parts
 splitTemplate :: Config -> [String]
diff --git a/src/Xmobar.hs b/src/Xmobar.hs
index d4aa083..30ad11e 100644
--- a/src/Xmobar.hs
+++ b/src/Xmobar.hs
@@ -40,6 +40,7 @@ import Control.Arrow ((&&&))
 import Control.Applicative ((<$>))
 import Control.Monad.Reader
 import Control.Concurrent
+import Control.Concurrent.Async (Async, async)
 import Control.Concurrent.STM
 import Control.Exception (handle, SomeException(..))
 import Data.Bits
@@ -89,7 +90,7 @@ runX :: XConf -> X () -> IO ()
 runX xc f = runReaderT f xc
 
 -- | Starts the main event loop and threads
-startLoop :: XConf -> TMVar SignalType -> [[(Maybe ThreadId, TVar String)]]
+startLoop :: XConf -> TMVar SignalType -> [[([Async ()], TVar String)]]
              -> IO ()
 startLoop xcfg@(XConf _ _ w _ _ _ _) sig vs = do
 #ifdef XFT
@@ -133,7 +134,7 @@ startLoop xcfg@(XConf _ _ w _ _ _ _) sig vs = do
 -- | Send signal to eventLoop every time a var is updated
 checker :: TVar [String]
            -> [String]
-           -> [[(Maybe ThreadId, TVar String)]]
+           -> [[([Async ()], TVar String)]]
            -> TMVar SignalType
            -> IO ()
 checker tvar ov vs signal = do
@@ -230,21 +231,21 @@ eventLoop tv xc@(XConf d r w fs vos is cfg) as signal = do
 
 -- $command
 
--- | Runs a command as an independent thread and returns its thread id
+-- | Runs a command as an independent thread and returns its Async handles
 -- and the TVar the command will be writing to.
 startCommand :: TMVar SignalType
              -> (Runnable,String,String)
-             -> IO (Maybe ThreadId, TVar String)
+             -> IO ([Async ()], TVar String)
 startCommand sig (com,s,ss)
     | alias com == "" = do var <- atomically $ newTVar is
                            atomically $ writeTVar var (s ++ ss)
-                           return (Nothing,var)
+                           return ([], var)
     | otherwise = do var <- atomically $ newTVar is
                      let cb str = atomically $ writeTVar var (s ++ str ++ ss)
-                     h <- forkIO $ start com cb
-                     _ <- forkIO $ trigger com $ maybe (return ())
+                     a1 <- async $ start com cb
+                     a2 <- async $ trigger com $ maybe (return ())
                                                  (atomically . putTMVar sig)
-                     return (Just h,var)
+                     return ([a1, a2], var)
     where is = s ++ "Updating..." ++ ss
 
 updateString :: Config -> TVar [String]
diff --git a/xmobar.cabal b/xmobar.cabal
index 1a3684c..5061507 100644
--- a/xmobar.cabal
+++ b/xmobar.cabal
@@ -187,7 +187,8 @@ executable xmobar
       mtl >= 2.1 && < 2.3,
       parsec == 3.1.*,
       parsec-numbers >= 0.1.0,
-      stm >= 2.3 && < 2.6
+      stm >= 2.3 && < 2.6,
+      async
 
     if impl(ghc < 8.0.2)
        -- Disable building with GHC before 8.0.2.
-- 
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