[demo] Verify signal state

Fix typo in test/group-session.sh

Trying to figure out why we need stop_process_hack() in
spec/stateful/harness.py

demo/cpython/fork_signal_state.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python2
+"""
+fork_signal_state.py
+"""
+from __future__ import print_function
+
+import os
+import signal
+import sys
+import time
+
+
+def log(msg, *args):
+  if args:
+    msg = msg % args
+  print(msg, file=sys.stderr)
+
+
+def SignalState(pid):
+  with open('/proc/%d/status' % pid) as f:
+    for line in f:
+      if line.startswith('Sig'):
+        print(line, end='')
+
+
+def main(argv):
+  parent_pid = os.getpid()
+  log('parent is %d', parent_pid)
+
+  # Hm this looks like it works
+  # Now why doesn't Ctrl-Z through the terminal work?  The process group should
+  # be controlling the terminal
+
+  # test/group-session.sh shows PGID and TPGID (controlling tty process group ID)
+
+  log('===')
+  SignalState(parent_pid)
+  signal.signal(signal.SIGTSTP, signal.SIG_IGN)
+  SignalState(parent_pid)
+  log('===')
+
+  pid = os.fork()
+  if pid == 0:
+    child_pid = os.getpid()
+
+    log('---')
+    SignalState(child_pid)
+    signal.signal(signal.SIGTSTP, signal.SIG_DFL)
+    SignalState(child_pid)
+    log('---')
+
+    log('sleep 1 in child %d', child_pid)
+    time.sleep(1)
+
+  elif pid < 0:
+    raise AssertionError()
+
+  else:
+    log('parent spawned %d', pid)
+
+    log('waiting')
+    result = os.waitpid(-1, 0)
+    log('wait => %s', result)
+
+
+if __name__ == '__main__':
+  try:
+    main(sys.argv)
+  except RuntimeError as e:
+    print('FATAL: %s' % e, file=sys.stderr)
+    sys.exit(1)

demo/cpython/signals.py → demo/cpython/keyboard_interrupt.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 """
-py_signals.py
+keyboard_interrupt.py: How to replace KeyboardInterrupt
 """
 from __future__ import print_function
 

test/group-session.sh

@@ -27,17 +27,17 @@ show_group_session() {
 
   case $kind in (*fgproc*)
     echo '[foreground process]'
-    ps -o pid,ppid,pgid,sid,tgid,comm
+    ps -o pid,ppid,pgid,sid,tpgid,comm
     ;;
   esac
 
   case $kind in (*bgproc*)
     echo '[background process]'
-    ps -o pid,ppid,pgid,sid,tgid,comm &
+    ps -o pid,ppid,pgid,sid,tpgid,comm &
     wait
 
     # - Gets its own PGID
-    # - Hm UNLIKE bgpipe it also gets its own TGID?  Seems consistent in all
+    # - Hm UNLIKE bgpipe it also gets its own TPGID?  Seems consistent in all
     #   shells.  Why is that?
     ;;
   esac