propagate signals to the transferrer process group

Done on unix, could not implement it on windows quite.

The signal library gets part of the way needed for windows.
But I had to open https://github.com/pmlodawski/signal/issues/1 because
it lacks raiseSignal.

Also, I don't know what the equivilant of getProcessGroupIDOf is on
windows. And System.Process does not provide a way to send any signal to
a process group except for SIGINT.

This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.

Annex/Action.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE CPP #-}
+
 module Annex.Action (
 	action,
 	verifiedAction,
@@ -25,6 +27,11 @@ import Annex.HashObject
 import Annex.CheckIgnore
 import Annex.TransferrerPool
 
+import Control.Concurrent.STM
+#ifndef mingw32_HOST_OS
+import System.Posix.Signals
+#endif
+
 {- Runs an action that may throw exceptions, catching and displaying them. -}
 action :: Annex () -> Annex Bool
 action a = tryNonAsync a >>= \case
@@ -43,13 +50,36 @@ verifiedAction a = tryNonAsync a >>= \case
 
 {- Actions to perform each time ran. -}
 startup :: Annex ()
-startup = return ()
+startup = do
+#ifndef mingw32_HOST_OS
+	av <- Annex.getState Annex.signalactions
+	let propagate sig = liftIO $ installhandleronce sig av
+	propagate sigINT
+	propagate sigQUIT
+	propagate sigTERM
+	propagate sigTSTP
+	propagate sigCONT
+	propagate sigHUP
+	-- sigWINCH is not propagated; it should not be needed,
+	-- and the concurrent-output library installs its own signal
+	-- handler for it.
+	-- sigSTOP and sigKILL cannot be caught, so will not be propagated.
+  where
+	installhandleronce sig av = void $
+		installHandler sig (CatchOnce (gotsignal sig av)) Nothing
+	gotsignal sig av = do
+		mapM_ (\a -> a (fromIntegral sig)) =<< atomically (readTVar av)
+		raiseSignal sig
+		installhandleronce sig av
+#else
+       return ()
+#endif
 
 {- Cleanup actions. -}
 shutdown :: Bool -> Annex ()
 shutdown nocommit = do
 	saveState nocommit
-	sequence_ =<< M.elems <$> Annex.getState Annex.cleanup
+	sequence_ =<< M.elems <$> Annex.getState Annex.cleanupactions
 	stopCoProcesses
 
 {- Stops all long-running child processes, including git query processes. -}