[test/stateful] Repro for SIGTSTP issue

Child processes appear to be ignoring it... why?  It seems like it could
be a Python interpreter thing, but I see no evidence of that.

demo/cpython/fork_signal_state.py

@@ -39,28 +39,43 @@ def main(argv):
   SignalState(parent_pid)
   log('===')
 
-  pid = os.fork()
-  if pid == 0:
-    child_pid = os.getpid()
+  line = raw_input()
 
-    log('---')
-    SignalState(child_pid)
-    signal.signal(signal.SIGTSTP, signal.SIG_DFL)
-    SignalState(child_pid)
-    log('---')
+  if line.startswith('sleep'):
+    pid = os.fork()
+    if pid == 0:
+      child_pid = os.getpid()
 
-    log('sleep 1 in child %d', child_pid)
-    time.sleep(1)
+      log('---')
+      SignalState(child_pid)
+      signal.signal(signal.SIGTSTP, signal.SIG_DFL)
+      SignalState(child_pid)
+      log('---')
 
-  elif pid < 0:
-    raise AssertionError()
+      log('sleep 1 in child %d', child_pid)
+      os.execve('/bin/sleep', ['sleep', '1'], {})
 
-  else:
-    log('parent spawned %d', pid)
+    elif pid < 0:
+      raise AssertionError()
+
+    else:
+      log('parent spawned %d', pid)
+
+      log('waiting')
+      pid, status = os.waitpid(-1, os.WUNTRACED)
+      log('wait => pid %d exited with status %d', pid, status)
+
+      if os.WIFEXITED(status):
+        log('EXITED')
 
-    log('waiting')
-    result = os.waitpid(-1, 0)
-    log('wait => %s', result)
+      if os.WIFSIGNALED(status):
+        log('SIGNALED')
+
+      elif os.WIFSTOPPED(status):
+        log('STOPPED')
+
+  else:
+    log('BAD COMMAND')
 
 
 if __name__ == '__main__':

spec/stateful/harness.py

@@ -33,20 +33,15 @@ def get_pid_by_name(name):
   return int(output.split()[-1])
 
 
-def send_signal(name, sig_num):
-  """Kill the most recent process matching `name`."""
-  os.kill(get_pid_by_name(name), sig_num)
-
-
-def stop_process__hack(name):
-  """Send sigstop to the most recent process matching `name`
+def stop_process__hack(name, sig_num=signal.SIGSTOP):
+  """Send SIGSTOP to the most recent process matching `name`
 
   Hack in place of sh.sendcontrol('z'), which sends SIGTSTP.  Why doesn't OSH
   respond to this, or why don't the child processes respond?
 
   TODO: Fix OSH and get rid of this hack.
   """
-  send_signal(name, signal.SIGSTOP)
+  os.kill(get_pid_by_name(name), sig_num)
 
 
 # Mutated by each test file.
@@ -235,11 +230,46 @@ def PrintResults(shell_pairs, result_table, flaky, num_retries, f):
   return num_failures
 
 
+def TestStop(exe):
+  p = pexpect.spawn(exe, encoding='utf-8', timeout=2.0)
+
+  # Show output
+  p.logfile = sys.stdout
+  #p.setecho(True)
+
+  p.sendline('sleep')
+  p.expect('in child')
+
+  import time
+  time.sleep(0.1)
+
+  # Stop it
+
+  if 0: # does NOT work -- why?
+    p.sendcontrol('z')
+  if 0: # does NOT work
+    stop_process__hack('sleep', sig_num=signal.SIGTSTP)
+  if 1:
+    # WORKS
+    stop_process__hack('sleep', sig_num=signal.SIGSTOP)
+
+  # These will kill the parent, not the sleep child
+  #p.kill(signal.SIGTSTP)
+  #p.kill(signal.SIGSTOP)
+
+  p.expect('wait =>')
+  p.close()
+
+
 def main(argv):
   # NOTE: Some options are ignored
   o = spec_lib.Options()
   opts, argv = o.parse_args(argv)
 
+  if argv and argv[1] == 'test-stop':  # Hack for testing
+    TestStop(argv[2])
+    return
+
   # List test cases and return
   if opts.do_list:
     for i, (desc, _, _) in enumerate(CASES):

spec/stateful/job_control.py

@@ -54,11 +54,23 @@ def bug_1004(sh):
 
   time.sleep(0.1)
 
-  if 0:
+  debug = False
+  #debug = True
+
+  if debug:
     import os
-    os.system('ls -l /proc/%s/fd' % os.getpid())
+    #os.system('ls -l /proc/%s/fd' % os.getpid())
 
-  if 0:
+    # From test/group-session.sh
+    log('harness PID = %d', os.getpid())
+    import subprocess
+    #os.system('ps -o pid,ppid,pgid,sid,tpgid,comm')
+
+    # the child shell is NOT LISTED here because it's associated WITH A
+    # DIFFERENT TERMINAL.
+    subprocess.call(['ps', '-o', 'pid,ppid,pgid,sid,tpgid,comm'])
+
+  if debug:
     ctrl_z(sh)
   else:
     stop_process__hack('cat')

test/stateful.sh

@@ -190,4 +190,12 @@ soil-run() {
   all
 }
 
+#
+# Debugging
+#
+
+test-stop() {
+  python3 spec/stateful/harness.py test-stop demo/cpython/fork_signal_state.py
+}
+
 "$@"