Fix zombie processes left by <action> tag and low battery action

This effectively reverts c54d93e and 991a168. While those fix #687 and
#688 respectively in the case where the configuration is recompiled, in
all other cases they leave zombie processes, since they undo the fix for
#181.

However, instead of reverting to the deprecated system function, we use
the newer spawnCommand and waitForProcess. And like with 991a168, the
low battery action now runs in the background to avoid blocking the bar.

3 files changed, 6 insertions, 5 deletions

diff --git a/changelog.md b/changelog.md
index 74912c6..6410188 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,6 +1,7 @@
 ## Version 0.48 (unreleased)
 
 - The `Kbd` monitor is not clickable (thanks, Enrico Maria)
+- Fix zombie processes left by `<action>` tag and low battery action
 
 ## Version 0.47.4 (March, 2024)
 
diff --git a/src/Xmobar/Plugins/Monitors/Batt/Common.hs b/src/Xmobar/Plugins/Monitors/Batt/Common.hs
index a07ba8b..ddb2b8c 100644
--- a/src/Xmobar/Plugins/Monitors/Batt/Common.hs
+++ b/src/Xmobar/Plugins/Monitors/Batt/Common.hs
@@ -18,7 +18,7 @@ module Xmobar.Plugins.Monitors.Batt.Common (BattOpts(..)
                                            , Status(..)
                                            , maybeAlert) where
 
-import System.Process (spawnCommand)
+import System.Process (spawnCommand, waitForProcess)
 import Control.Monad (unless, void)
 import Xmobar.Plugins.Monitors.Common
 
@@ -54,4 +54,4 @@ maybeAlert opts left =
   case onLowAction opts of
     Nothing -> return ()
     Just x -> unless (isNaN left || actionThreshold opts < 100 * left)
-                $ void $ spawnCommand x
+                $ void $ spawnCommand (x ++ " &") >>= waitForProcess
diff --git a/src/Xmobar/Run/Actions.hs b/src/Xmobar/Run/Actions.hs
index 51dbb85..cbc10c5 100644
--- a/src/Xmobar/Run/Actions.hs
+++ b/src/Xmobar/Run/Actions.hs
@@ -16,7 +16,7 @@ module Xmobar.Run.Actions ( Button
                           , runAction'
                           , stripActions) where
 
-import System.Process (spawnCommand)
+import System.Process (spawnCommand, waitForProcess)
 import Control.Monad (void)
 import Text.Regex (Regex, subRegex, mkRegex, matchRegex)
 import Data.Word (Word32)
@@ -26,11 +26,11 @@ type Button = Word32
 data Action = Spawn [Button] String deriving (Eq, Read, Show)
 
 runAction :: Action -> IO ()
-runAction (Spawn _ s) = void $ spawnCommand s
+runAction (Spawn _ s) = void $ spawnCommand (s ++ " &") >>= waitForProcess
 
 -- | Run action with stdout redirected to stderr
 runAction' :: Action -> IO ()
-runAction' (Spawn _ s) = void $ spawnCommand (s ++ " 1>&2")
+runAction' (Spawn _ s) = void $ spawnCommand (s ++ " 1>&2 &") >>= waitForProcess
 
 stripActions :: String -> String
 stripActions s = case matchRegex actionRegex s of