Fix bpo-30596: Add close() method to multiprocessing.Process (#2010)
* Fix bpo-30596: Add close() method to multiprocessing.Process
* Raise ValueError if close() is called before the Process is finished running
* Add docs
* Add NEWS blurb
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 6b4a8cb..5265639 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -598,6 +598,16 @@
acquired a lock or semaphore etc. then terminating it is liable to
cause other processes to deadlock.
+ .. method:: close()
+
+ Close the :class:`Process` object, releasing all resources associated
+ with it. :exc:`ValueError` is raised if the underlying process
+ is still running. Once :meth:`close` returns successfully, most
+ other methods and attributes of the :class:`Process` object will
+ raise :exc:`ValueError`.
+
+ .. versionadded:: 3.7
+
Note that the :meth:`start`, :meth:`join`, :meth:`is_alive`,
:meth:`terminate` and :attr:`exitcode` methods should only be called by
the process that created the process object.
diff --git a/Lib/multiprocessing/forkserver.py b/Lib/multiprocessing/forkserver.py
index 7010515..b9f9b9d 100644
--- a/Lib/multiprocessing/forkserver.py
+++ b/Lib/multiprocessing/forkserver.py
@@ -210,8 +210,12 @@
else:
assert os.WIFEXITED(sts)
returncode = os.WEXITSTATUS(sts)
- # Write the exit code to the pipe
- write_signed(child_w, returncode)
+ # Send exit code to client process
+ try:
+ write_signed(child_w, returncode)
+ except BrokenPipeError:
+ # client vanished
+ pass
os.close(child_w)
else:
# This shouldn't happen really
@@ -241,8 +245,12 @@
finally:
os._exit(code)
else:
- # Send pid to client processes
- write_signed(child_w, pid)
+ # Send pid to client process
+ try:
+ write_signed(child_w, pid)
+ except BrokenPipeError:
+ # client vanished
+ pass
pid_to_fd[pid] = child_w
os.close(child_r)
for fd in fds:
diff --git a/Lib/multiprocessing/popen_fork.py b/Lib/multiprocessing/popen_fork.py
index ca28bf3..5af9d91 100644
--- a/Lib/multiprocessing/popen_fork.py
+++ b/Lib/multiprocessing/popen_fork.py
@@ -17,6 +17,7 @@
sys.stdout.flush()
sys.stderr.flush()
self.returncode = None
+ self.finalizer = None
self._launch(process_obj)
def duplicate_for_child(self, fd):
@@ -70,5 +71,9 @@
os._exit(code)
else:
os.close(child_w)
- util.Finalize(self, os.close, (parent_r,))
+ self.finalizer = util.Finalize(self, os.close, (parent_r,))
self.sentinel = parent_r
+
+ def close(self):
+ if self.finalizer is not None:
+ self.finalizer()
diff --git a/Lib/multiprocessing/popen_forkserver.py b/Lib/multiprocessing/popen_forkserver.py
index fa8e574..a51a277 100644
--- a/Lib/multiprocessing/popen_forkserver.py
+++ b/Lib/multiprocessing/popen_forkserver.py
@@ -49,7 +49,7 @@
set_spawning_popen(None)
self.sentinel, w = forkserver.connect_to_new_process(self._fds)
- util.Finalize(self, os.close, (self.sentinel,))
+ self.finalizer = util.Finalize(self, os.close, (self.sentinel,))
with open(w, 'wb', closefd=True) as f:
f.write(buf.getbuffer())
self.pid = forkserver.read_signed(self.sentinel)
diff --git a/Lib/multiprocessing/popen_spawn_posix.py b/Lib/multiprocessing/popen_spawn_posix.py
index 98f8f0a..3815106 100644
--- a/Lib/multiprocessing/popen_spawn_posix.py
+++ b/Lib/multiprocessing/popen_spawn_posix.py
@@ -62,7 +62,7 @@
f.write(fp.getbuffer())
finally:
if parent_r is not None:
- util.Finalize(self, os.close, (parent_r,))
+ self.finalizer = util.Finalize(self, os.close, (parent_r,))
for fd in (child_r, child_w, parent_w):
if fd is not None:
os.close(fd)
diff --git a/Lib/multiprocessing/popen_spawn_win32.py b/Lib/multiprocessing/popen_spawn_win32.py
index 6fd588f..ecb86e9 100644
--- a/Lib/multiprocessing/popen_spawn_win32.py
+++ b/Lib/multiprocessing/popen_spawn_win32.py
@@ -56,7 +56,7 @@
self.returncode = None
self._handle = hp
self.sentinel = int(hp)
- util.Finalize(self, _winapi.CloseHandle, (self.sentinel,))
+ self.finalizer = util.Finalize(self, _winapi.CloseHandle, (self.sentinel,))
# send information to child
set_spawning_popen(self)
@@ -96,3 +96,6 @@
except OSError:
if self.wait(timeout=1.0) is None:
raise
+
+ def close(self):
+ self.finalizer()
diff --git a/Lib/multiprocessing/process.py b/Lib/multiprocessing/process.py
index 37365f2..70bb50d 100644
--- a/Lib/multiprocessing/process.py
+++ b/Lib/multiprocessing/process.py
@@ -76,6 +76,7 @@
self._config = _current_process._config.copy()
self._parent_pid = os.getpid()
self._popen = None
+ self._closed = False
self._target = target
self._args = tuple(args)
self._kwargs = dict(kwargs)
@@ -85,6 +86,10 @@
self.daemon = daemon
_dangling.add(self)
+ def _check_closed(self):
+ if self._closed:
+ raise ValueError("process object is closed")
+
def run(self):
'''
Method to be run in sub-process; can be overridden in sub-class
@@ -96,6 +101,7 @@
'''
Start child process
'''
+ self._check_closed()
assert self._popen is None, 'cannot start a process twice'
assert self._parent_pid == os.getpid(), \
'can only start a process object created by current process'
@@ -110,12 +116,14 @@
'''
Terminate process; sends SIGTERM signal or uses TerminateProcess()
'''
+ self._check_closed()
self._popen.terminate()
def join(self, timeout=None):
'''
Wait until child process terminates
'''
+ self._check_closed()
assert self._parent_pid == os.getpid(), 'can only join a child process'
assert self._popen is not None, 'can only join a started process'
res = self._popen.wait(timeout)
@@ -126,6 +134,7 @@
'''
Return whether process is alive
'''
+ self._check_closed()
if self is _current_process:
return True
assert self._parent_pid == os.getpid(), 'can only test a child process'
@@ -134,6 +143,23 @@
self._popen.poll()
return self._popen.returncode is None
+ def close(self):
+ '''
+ Close the Process object.
+
+ This method releases resources held by the Process object. It is
+ an error to call this method if the child process is still running.
+ '''
+ if self._popen is not None:
+ if self._popen.poll() is None:
+ raise ValueError("Cannot close a process while it is still running. "
+ "You should first call join() or terminate().")
+ self._popen.close()
+ self._popen = None
+ del self._sentinel
+ _children.discard(self)
+ self._closed = True
+
@property
def name(self):
return self._name
@@ -174,6 +200,7 @@
'''
Return exit code of process or `None` if it has yet to stop
'''
+ self._check_closed()
if self._popen is None:
return self._popen
return self._popen.poll()
@@ -183,6 +210,7 @@
'''
Return identifier (PID) of process or `None` if it has yet to start
'''
+ self._check_closed()
if self is _current_process:
return os.getpid()
else:
@@ -196,6 +224,7 @@
Return a file descriptor (Unix) or handle (Windows) suitable for
waiting for process termination.
'''
+ self._check_closed()
try:
return self._sentinel
except AttributeError:
@@ -204,6 +233,8 @@
def __repr__(self):
if self is _current_process:
status = 'started'
+ elif self._closed:
+ status = 'closed'
elif self._parent_pid != os.getpid():
status = 'unknown'
elif self._popen is None:
@@ -295,6 +326,7 @@
self._name = 'MainProcess'
self._parent_pid = None
self._popen = None
+ self._closed = False
self._config = {'authkey': AuthenticationString(os.urandom(32)),
'semprefix': '/mp'}
# Note that some versions of FreeBSD only allow named
@@ -307,6 +339,9 @@
# Everything in self._config will be inherited by descendant
# processes.
+ def close(self):
+ pass
+
_current_process = _MainProcess()
_process_counter = itertools.count(1)
diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index 7148ea4..d4a461d 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -403,6 +403,42 @@
p.join()
self.assertTrue(wait_for_handle(sentinel, timeout=1))
+ @classmethod
+ def _test_close(cls, rc=0, q=None):
+ if q is not None:
+ q.get()
+ sys.exit(rc)
+
+ def test_close(self):
+ if self.TYPE == "threads":
+ self.skipTest('test not appropriate for {}'.format(self.TYPE))
+ q = self.Queue()
+ p = self.Process(target=self._test_close, kwargs={'q': q})
+ p.daemon = True
+ p.start()
+ self.assertEqual(p.is_alive(), True)
+ # Child is still alive, cannot close
+ with self.assertRaises(ValueError):
+ p.close()
+
+ q.put(None)
+ p.join()
+ self.assertEqual(p.is_alive(), False)
+ self.assertEqual(p.exitcode, 0)
+ p.close()
+ with self.assertRaises(ValueError):
+ p.is_alive()
+ with self.assertRaises(ValueError):
+ p.join()
+ with self.assertRaises(ValueError):
+ p.terminate()
+ p.close()
+
+ wr = weakref.ref(p)
+ del p
+ gc.collect()
+ self.assertIs(wr(), None)
+
def test_many_processes(self):
if self.TYPE == 'threads':
self.skipTest('test not appropriate for {}'.format(self.TYPE))
diff --git a/Misc/NEWS.d/next/Library/2017-06-24-18-55-58.bpo-30596.VhB8iG.rst b/Misc/NEWS.d/next/Library/2017-06-24-18-55-58.bpo-30596.VhB8iG.rst
new file mode 100644
index 0000000..6b9e9a1
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-06-24-18-55-58.bpo-30596.VhB8iG.rst
@@ -0,0 +1 @@
+Add a ``close()`` method to ``multiprocessing.Process``.