Merge pull request #10 from denibertovic/master

Adds ability to only SIGTERM the immediate process

Author: snoyberg

README.md

@@ -34,6 +34,15 @@ Where:
 * `-w`, `--workdir` `DIR` - chdir to `DIR` before executing COMMAND
 * `-t`, `--timeout` `TIMEOUT` - timeout (in seconds) to wait for all child processes to exit
 
+`WARNING`: by default pid1 will first send the TERM signal to it's "immediate child" process.
+In most scenarios that will be the only process running but in some cases that will be the
+"main" process that could have spawned it's own children. In this scenario it's prudent to shutdown
+the "main" process first, since usually it has mechanisms in place to shut down it's children. If
+we were to shutdown a child process before "main" was shutdown it might try to restart it.
+This is why, if the "main" process doesn't exit within `timeout` we will proceed to send the TERM
+signal to all processes and wait **again** for `timeout` until we finally send the KILL signal to all
+processes. This is a **breaking change since 0.1.3.0**.
+
 The recommended use case for this executable is to embed it in a Docker image.
 Assuming you've placed it at `/sbin/pid1`, the two commonly recommended usages
 are:

pid1.cabal

@@ -1,5 +1,5 @@
 name:                pid1
-version:             0.1.2.0
+version:             0.1.3.0
 synopsis:            Do signal handling and orphan reaping for Unix PID1 init processes
 description:         Please see README.md or view Haddocks at <https://www.stackage.org/package/pid1>
 homepage:            https://github.com/fpco/pid1#readme

src/System/Process/PID1.hs

@@ -181,9 +181,6 @@ runAsPID1 cmd args env' timeout = do
     -- children processes. Then start a thread waiting for that
     -- variable to be filled and do the actual killing.
     killChildrenVar <- newEmptyMVar
-    _ <- forkIO $ do
-        takeMVar killChildrenVar
-        killAllChildren timeout
 
     -- Helper function to start killing, used below
     let startKilling = void $ tryPutMVar killChildrenVar ()
@@ -206,6 +203,10 @@ runAsPID1 cmd args env' timeout = do
             ClosedHandle e -> assert False (exitWith e)
             OpenHandle pid -> return pid
 
+    _ <- forkIO $ do
+        takeMVar killChildrenVar
+        killAllChildren child timeout
+
     -- Loop on reaping child processes
     reap startKilling child
 
@@ -247,9 +248,20 @@ reap startKilling child = do
                     startKilling
                 | otherwise -> return ()
 
-killAllChildren :: Int -> IO ()
-killAllChildren timeout = do
-    -- Send all children processes the TERM signal
+killAllChildren :: CPid -> Int -> IO ()
+killAllChildren cid timeout = do
+    -- Send the direct child process the TERM signal
+    signalProcess sigTERM cid `catch` \e ->
+        if isDoesNotExistError e
+            then return ()
+            else throwIO e
+
+    -- Wait for `timeout` seconds and allow the 'main' process to take care
+    -- of shutting down any child processes itself.
+    threadDelay $ timeout * 1000 * 1000
+
+    -- If the 'main' process did not handle shutting down the rest of the
+    -- child processes we will signal SIGTERM to them directly.
     signalProcess sigTERM (-1) `catch` \e ->
         if isDoesNotExistError e
             then return ()