Issue #15064: Implement context manager protocol for multiprocessing types

Doc/library/multiprocessing.rst

@@ -834,6 +834,10 @@ Connection objects are usually created using :func:`Pipe` -- see also
       Connection objects themselves can now be transferred between processes
       using :meth:`Connection.send` and :meth:`Connection.recv`.
 
+   .. versionadded:: 3.3
+      Connection objects now support the context manager protocol -- see
+      :ref:`typecontextmanager`.  :meth:`__enter__` returns the
+      connection object, and :meth:`__exit__` calls :meth:`close`.
 
 For example:
 
@@ -1277,6 +1281,9 @@ their parent process exits.  The manager classes are defined in the
 
       The address used by the manager.
 
+   Manager objects support the context manager protocol -- see
+   :ref:`typecontextmanager`.  :meth:`__enter__` returns the
+   manager object, and :meth:`__exit__` calls :meth:`shutdown`.
 
 .. class:: SyncManager
 
@@ -1747,6 +1754,11 @@ with the :class:`Pool` class.
       Wait for the worker processes to exit.  One must call :meth:`close` or
       :meth:`terminate` before using :meth:`join`.
 
+   .. versionadded:: 3.3
+      Pool objects now support the context manager protocol -- see
+      :ref:`typecontextmanager`.  :meth:`__enter__` returns the pool
+      object, and :meth:`__exit__` calls :meth:`terminate`.
+
 
 .. class:: AsyncResult
 
@@ -1911,6 +1923,11 @@ multiple connections at the same time.
       The address from which the last accepted connection came.  If this is
       unavailable then it is ``None``.
 
+   .. versionadded:: 3.3
+      Listener objects now support the context manager protocol -- see
+      :ref:`typecontextmanager`.  :meth:`__enter__` returns the
+      listener object, and :meth:`__exit__` calls :meth:`close`.
+
 .. function:: wait(object_list, timeout=None)
 
    Wait till an object in *object_list* is ready.  Returns the list of

Lib/multiprocessing/connection.py

@@ -257,6 +257,12 @@ class _ConnectionBase:
         self._check_readable()
         return self._poll(timeout)
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self.close()
+
 
 if _winapi:
 
@@ -436,6 +442,8 @@ class Listener(object):
 
         Returns a `Connection` object.
         '''
+        if self._listener is None:
+            raise IOError('listener is closed')
         c = self._listener.accept()
         if self._authkey:
             deliver_challenge(c, self._authkey)
@@ -446,11 +454,19 @@ class Listener(object):
         '''
         Close the bound socket or named pipe of `self`.
         '''
-        return self._listener.close()
+        if self._listener is not None:
+            self._listener.close()
+            self._listener = None
 
     address = property(lambda self: self._listener._address)
     last_accepted = property(lambda self: self._listener._last_accepted)
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self.close()
+
 
 def Client(address, family=None, authkey=None):
     '''

Lib/multiprocessing/dummy/connection.py

@@ -53,6 +53,12 @@ class Listener(object):
 
     address = property(lambda self: self._backlog_queue)
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self.close()
+
 
 def Client(address):
     _in, _out = Queue(), Queue()
@@ -85,3 +91,9 @@ class Connection(object):
 
     def close(self):
         pass
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self.close()

Lib/multiprocessing/pool.py

@@ -522,6 +522,12 @@ class Pool(object):
                     debug('cleaning up worker %d' % p.pid)
                     p.join()
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.terminate()
+
 #
 # Class whose instances are returned by `Pool.apply_async()`
 #

Lib/test/test_multiprocessing.py

@@ -1719,6 +1719,15 @@ class _TestPool(BaseTestCase):
         p.close()
         p.join()
 
+    def test_context(self):
+        if self.TYPE == 'processes':
+            L = list(range(10))
+            expected = [sqr(i) for i in L]
+            with multiprocessing.Pool(2) as p:
+                r = p.map_async(sqr, L)
+                self.assertEqual(r.get(), expected)
+            self.assertRaises(AssertionError, p.map_async, sqr, L)
+
 def raising():
     raise KeyError("key")
 
@@ -2266,6 +2275,22 @@ class _TestConnection(BaseTestCase):
         self.assertRaises(RuntimeError, reduction.recv_handle, conn)
         p.join()
 
+    def test_context(self):
+        a, b = self.Pipe()
+
+        with a, b:
+            a.send(1729)
+            self.assertEqual(b.recv(), 1729)
+            if self.TYPE == 'processes':
+                self.assertFalse(a.closed)
+                self.assertFalse(b.closed)
+
+        if self.TYPE == 'processes':
+            self.assertTrue(a.closed)
+            self.assertTrue(b.closed)
+            self.assertRaises(IOError, a.recv)
+            self.assertRaises(IOError, b.recv)
+
 class _TestListener(BaseTestCase):
 
     ALLOWED_TYPES = ('processes',)
@@ -2277,6 +2302,16 @@ class _TestListener(BaseTestCase):
             self.assertRaises(OSError, self.connection.Listener,
                               l.address, family)
 
+    def test_context(self):
+        with self.connection.Listener() as l:
+            with self.connection.Client(l.address) as c:
+                with l.accept() as d:
+                    c.send(1729)
+                    self.assertEqual(d.recv(), 1729)
+
+        if self.TYPE == 'processes':
+            self.assertRaises(IOError, l.accept)
+
 class _TestListenerClient(BaseTestCase):
 
     ALLOWED_TYPES = ('processes', 'threads')

Misc/NEWS

@@ -29,6 +29,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #15064: Implement context manager protocol for multiprocessing types
+
 - Issue #15101: Make pool finalizer avoid joining current thread.
 
 - Issue #14657: The frozen instance of importlib used for bootstrap is now