bpo-36888: Add multiprocessing.parent_process()

Doc/library/multiprocessing.rst

@@ -944,6 +944,14 @@ Miscellaneous
 
  An analogue of :func:`threading.current_thread`.
 
+.. function:: parent_process()
+
+ Return the :class:`Process` object corresponding to the parent process of
+ the :func:`current_process`. For the main process, ``parent_process`` will
+ be ``None``.
+
+ .. versionadded:: 3.8
+
 .. function:: freeze_support()
 
  Add support for when a program which uses :mod:`multiprocessing` has been

Lib/multiprocessing/context.py

@@ -35,6 +35,7 @@ class BaseContext(object):
  AuthenticationError = AuthenticationError
 
  current_process = staticmethod(process.current_process)
+ parent_process = staticmethod(process.parent_process)
  active_children = staticmethod(process.active_children)
 
  def cpu_count(self):

Lib/multiprocessing/forkserver.py

@@ -294,7 +294,8 @@ def _serve_one(child_r, fds, unused_fds, handlers):
  *_forkserver._inherited_fds) = fds
 
  # Run process object received over pipe
- code = spawn._main(child_r)
+ parent_sentinel = os.dup(child_r)
+ code = spawn._main(child_r, parent_sentinel)
 
  return code
 

Lib/multiprocessing/popen_fork.py

@@ -66,16 +66,20 @@ def kill(self):
  def _launch(self, process_obj):
  code = 1
  parent_r, child_w = os.pipe()
+ child_r, parent_w = os.pipe()
  self.pid = os.fork()
  if self.pid == 0:
  try:
  os.close(parent_r)
- code = process_obj._bootstrap()
+ os.close(parent_w)
+ code = process_obj._bootstrap(parent_sentinel=child_r)
  finally:
  os._exit(code)
  else:
  os.close(child_w)
- self.finalizer = util.Finalize(self, os.close, (parent_r,))
+ os.close(child_r)
+ self.finalizer = util.Finalize(self, util.close_fds,
+ (parent_r, parent_w,))
  self.sentinel = parent_r
 
  def close(self):

Lib/multiprocessing/popen_forkserver.py

@@ -49,7 +49,11 @@ def _launch(self, process_obj):
  set_spawning_popen(None)
 
  self.sentinel, w = forkserver.connect_to_new_process(self._fds)
- self.finalizer = util.Finalize(self, os.close, (self.sentinel,))
+ # Keep a duplicate of the data pipe's write end as a sentinel of the
+ # parent process used by the child process.
+ _parent_w = os.dup(w)
+ self.finalizer = util.Finalize(self, util.close_fds,
+ (_parent_w, self.sentinel))
  with open(w, 'wb', closefd=True) as f:
  f.write(buf.getbuffer())
  self.pid = forkserver.read_signed(self.sentinel)

Lib/multiprocessing/popen_spawn_posix.py

@@ -61,8 +61,12 @@ def _launch(self, process_obj):
  with open(parent_w, 'wb', closefd=False) as f:
  f.write(fp.getbuffer())
  finally:
- if parent_r is not None:
- self.finalizer = util.Finalize(self, os.close, (parent_r,))
- for fd in (child_r, child_w, parent_w):
+ fds_to_close = []
+ for fd in (parent_r, parent_w):
+ if fd is not None:
+ fds_to_close.append(fd)
+ self.finalizer = util.Finalize(self, util.close_fds, fds_to_close)
+
+ for fd in (child_r, child_w):
  if fd is not None:
  os.close(fd)

Lib/multiprocessing/process.py

@@ -7,7 +7,8 @@
 # Licensed to PSF under a Contributor Agreement.
 #
 
-__all__ = ['BaseProcess', 'current_process', 'active_children']
+__all__ = ['BaseProcess', 'current_process', 'active_children',
+ 'parent_process']
 
 #
 # Imports
@@ -46,6 +47,13 @@ def active_children():
  _cleanup()
  return list(_children)
 
+
+def parent_process():
+ '''
+ Return process object representing the parent process
+ '''
+ return _parent_process
+
 #
 #
 #
@@ -76,6 +84,7 @@ def __init__(self, group=None, target=None, name=None, args=(), kwargs={},
  self._identity = _current_process._identity + (count,)
  self._config = _current_process._config.copy()
  self._parent_pid = os.getpid()
+ self._parent_name = _current_process.name
  self._popen = None
  self._closed = False
  self._target = target
@@ -278,9 +287,9 @@ def __repr__(self):
 
  ##
 
- def _bootstrap(self):
+ def _bootstrap(self, parent_sentinel=None):
  from . import util, context
- global _current_process, _process_counter, _children
+ global _current_process, _parent_process, _process_counter, _children
 
  try:
  if self._start_method is not None:
@@ -290,6 +299,8 @@ def _bootstrap(self):
  util._close_stdin()
  old_process = _current_process
  _current_process = self
+ _parent_process = _ParentProcess(
+ self._parent_name, self._parent_pid, parent_sentinel)
  try:
  util._finalizer_registry.clear()
  util._run_after_forkers()
@@ -337,6 +348,40 @@ def __reduce__(self):
  )
  return AuthenticationString, (bytes(self),)
 
+
+#
+# Create object representing the parent process
+#
+
+class _ParentProcess(BaseProcess):
+
+ def __init__(self, name, pid, sentinel):
+ self._identity = ()
+ self._name = name
+ self._pid = pid
+ self._parent_pid = None
+ self._popen = None
+ self._closed = False
+ self._sentinel = sentinel
+ self._config = {}
+
+ def is_alive(self):
+ from multiprocessing.connection import wait
+ return not wait([self._sentinel], timeout=0)
+
+ @property
+ def ident(self):
+ return self._pid
+
+ def join(self, timeout=None):
+ '''
+ Wait until parent process terminates
+ '''
+ from multiprocessing.connection import wait
+ wait([self._sentinel], timeout=timeout)
+
+ pid = ident
+
 #
 # Create object representing the main process
 #
@@ -365,6 +410,7 @@ def close(self):
  pass
 
 
+_parent_process = None
 _current_process = _MainProcess()
 _process_counter = itertools.count(1)
 _children = set()

Lib/multiprocessing/spawn.py

@@ -100,25 +100,24 @@ def spawn_main(pipe_handle, parent_pid=None, tracker_fd=None):
 
  if parent_pid is not None:
  source_process = _winapi.OpenProcess(
- _winapi.PROCESS_DUP_HANDLE, False, parent_pid)
+ _winapi.SYNCHRONIZE | _winapi.PROCESS_DUP_HANDLE,
+ False, parent_pid)
  else:
  source_process = None
- try:
- new_handle = reduction.duplicate(pipe_handle,
- source_process=source_process)
- finally:
- if source_process is not None:
- _winapi.CloseHandle(source_process)
+ new_handle = reduction.duplicate(pipe_handle,
+ source_process=source_process)
  fd = msvcrt.open_osfhandle(new_handle, os.O_RDONLY)
+ parent_sentinel = source_process
  else:
  from . import resource_tracker
  resource_tracker._resource_tracker._fd = tracker_fd
  fd = pipe_handle
- exitcode = _main(fd)
+ parent_sentinel = os.dup(pipe_handle)
+ exitcode = _main(fd, parent_sentinel)
  sys.exit(exitcode)
 
 
-def _main(fd):
+def _main(fd, parent_sentinel):
  with os.fdopen(fd, 'rb', closefd=True) as from_parent:
  process.current_process()._inheriting = True
  try:
@@ -127,7 +126,7 @@ def _main(fd):
  self = reduction.pickle.load(from_parent)
  finally:
  del process.current_process()._inheriting
- return self._bootstrap()
+ return self._bootstrap(parent_sentinel)
 
 
 def _check_not_importing_main():

Lib/multiprocessing/util.py

@@ -421,3 +421,9 @@ def spawnv_passfds(path, args, passfds):
  finally:
  os.close(errpipe_read)
  os.close(errpipe_write)
+
+
+def close_fds(*fds):
+ """Close each file descriptor given as an argument"""
+ for fd in fds:
+ os.close(fd)

Lib/test/_test_multiprocessing.py

@@ -269,6 +269,64 @@ def _test(cls, q, *args, **kwds):
  q.put(bytes(current.authkey))
  q.put(current.pid)
 
+ def test_parent_process_attributes(self):
+ if self.TYPE == "threads":
+ self.skipTest('test not appropriate for {}'.format(self.TYPE))
+
+ self.assertIsNone(self.parent_process())
+
+ rconn, wconn = self.Pipe(duplex=False)
+ p = self.Process(target=self._test_send_parent_process, args=(wconn,))
+ p.start()
+ p.join()
+ parent_pid, parent_name = rconn.recv()
+ self.assertEqual(parent_pid, self.current_process().pid)
+ self.assertEqual(parent_pid, os.getpid())
+ self.assertEqual(parent_name, self.current_process().name)
+
+ @classmethod
+ def _test_send_parent_process(cls, wconn):
+ from multiprocessing.process import parent_process
+ wconn.send([parent_process().pid, parent_process().name])
+
+ def test_parent_process(self):
+ if self.TYPE == "threads":
+ self.skipTest('test not appropriate for {}'.format(self.TYPE))
+
+ # Launch a child process. Make it launch a grandchild process. Kill the
+ # child process and make sure that the grandchild notices the death of
+ # its parent (a.k.a the child process).
+ rconn, wconn = self.Pipe(duplex=False)
+ p = self.Process(
+ target=self._test_create_grandchild_process, args=(wconn, ))
+ p.start()
+
+ if not rconn.poll(timeout=5):
+ raise AssertionError("Could not communicate with child process")
+ parent_process_status = rconn.recv()
+ self.assertEqual(parent_process_status, "alive")
+
+ p.terminate()
+ p.join()
+
+ if not rconn.poll(timeout=5):
+ raise AssertionError("Could not communicate with child process")
+ parent_process_status = rconn.recv()
+ self.assertEqual(parent_process_status, "not alive")
+
+ @classmethod
+ def _test_create_grandchild_process(cls, wconn):
+ p = cls.Process(target=cls._test_report_parent_status, args=(wconn, ))
+ p.start()
+ time.sleep(100)
+
+ @classmethod
+ def _test_report_parent_status(cls, wconn):
+ from multiprocessing.process import parent_process
+ wconn.send("alive" if parent_process().is_alive() else "not alive")
+ parent_process().join(timeout=5)
+ wconn.send("alive" if parent_process().is_alive() else "not alive")
+
  def test_process(self):
  q = self.Queue(1)
  e = self.Event()
@@ -5390,6 +5448,7 @@ class ProcessesMixin(BaseMixin):
  Process = multiprocessing.Process
  connection = multiprocessing.connection
  current_process = staticmethod(multiprocessing.current_process)
+ parent_process = staticmethod(multiprocessing.parent_process)
  active_children = staticmethod(multiprocessing.active_children)
  Pool = staticmethod(multiprocessing.Pool)
  Pipe = staticmethod(multiprocessing.Pipe)

Misc/NEWS.d/next/Library/2019-05-16-18-02-08.bpo-36888.-H2Dkm.rst

@@ -0,0 +1,2 @@
+Python child processes can now access the status of their parent process
+using multiprocessing.process.parent_process

Modules/_winapi.c

@@ -1955,6 +1955,7 @@ PyInit__winapi(void)
  WINAPI_CONSTANT(F_DWORD, PIPE_UNLIMITED_INSTANCES);
  WINAPI_CONSTANT(F_DWORD, PIPE_WAIT);
  WINAPI_CONSTANT(F_DWORD, PROCESS_ALL_ACCESS);
+ WINAPI_CONSTANT(F_DWORD, SYNCHRONIZE);
  WINAPI_CONSTANT(F_DWORD, PROCESS_DUP_HANDLE);
  WINAPI_CONSTANT(F_DWORD, SEC_COMMIT);
  WINAPI_CONSTANT(F_DWORD, SEC_IMAGE);