From c8e9ab4ca91a0d81063c271c4353da656f827b6b Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Tue, 12 Mar 2024 09:40:51 +0100
Subject: [PATCH] kernel: kill subprocess before closing pipe to it (#5666)

Otherwise we see issues like this on Linux:

    gap> d := DirectoryCurrent();;
    gap> f := Filename(DirectoriesSystemPrograms(), "rev");;
    gap> s := InputOutputLocalProcess(d,f,[]);;
    gap> Sleep(1);
    gap> CloseStream(s); Print("\n");
    rev: stdin
---
 src/iostream.c                      | 2 +-
 tst/testspecial/child-process.g     | 5 +++++
 tst/testspecial/child-process.g.out | 7 +++++++
 3 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 tst/testspecial/child-process.g
 create mode 100644 tst/testspecial/child-process.g.out

diff --git a/src/iostream.c b/src/iostream.c
index 60ac7db611..18db099015 100644
--- a/src/iostream.c
+++ b/src/iostream.c
@@ -1010,10 +1010,10 @@ static Obj FuncCLOSE_PTY_IOSTREAM(Obj self, Obj stream)
 
     // Close down the child
     int status;
+    kill(PtyIOStreams[pty].childPID, SIGTERM);
     int retcode = close(PtyIOStreams[pty].ptyFD);
     if (retcode)
         Pr("Strange close return code %d\n", retcode, 0);
-    kill(PtyIOStreams[pty].childPID, SIGTERM);
     // GAP (or another library) might wait on this PID before
     // we handle it. If that happens, waitpid will return -1.
     retcode = waitpid(PtyIOStreams[pty].childPID, &status, WNOHANG);
diff --git a/tst/testspecial/child-process.g b/tst/testspecial/child-process.g
new file mode 100644
index 0000000000..caf1f71ae8
--- /dev/null
+++ b/tst/testspecial/child-process.g
@@ -0,0 +1,5 @@
+d := DirectoryCurrent();;
+f := Filename(DirectoriesSystemPrograms(), "rev");;
+s := InputOutputLocalProcess(d,f,[]);;
+Sleep(1);
+CloseStream(s); Print("\n");
diff --git a/tst/testspecial/child-process.g.out b/tst/testspecial/child-process.g.out
new file mode 100644
index 0000000000..27291b989a
--- /dev/null
+++ b/tst/testspecial/child-process.g.out
@@ -0,0 +1,7 @@
+gap> d := DirectoryCurrent();;
+gap> f := Filename(DirectoriesSystemPrograms(), "rev");;
+gap> s := InputOutputLocalProcess(d,f,[]);;
+gap> Sleep(1);
+gap> CloseStream(s); Print("\n");
+
+gap> QUIT;