bpo-36888: Add multiprocessing.parent_process() (GH-13247)

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()
@@ -5398,6 +5456,7 @@ 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);