From b3f592acee44ffc469d2773a69bd8ddf0f2e2902 Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 01:41:40 +0000
Subject: [PATCH 01/10] issue #535: core/select: support selecting from
 Latches.

---
 mitogen/core.py      |   4 +
 mitogen/select.py    |  86 ++++++++++++++++----
 tests/select_test.py | 189 ++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 254 insertions(+), 25 deletions(-)

diff --git a/mitogen/core.py b/mitogen/core.py
index 25732896..6bca1b1a 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -2051,6 +2051,8 @@ class Latch(object):
     """
     poller_class = Poller
 
+    notify = None
+
     # The _cls_ prefixes here are to make it crystal clear in the code which
     # state mutation isn't covered by :attr:`_lock`.
 
@@ -2264,6 +2266,8 @@ class Latch(object):
                 _vv and IOLOG.debug('%r.put() -> waking wfd=%r',
                                     self, wsock.fileno())
                 self._wake(wsock, cookie)
+            elif self.notify:
+                self.notify(self)
         finally:
             self._lock.release()
 
diff --git a/mitogen/select.py b/mitogen/select.py
index fd2cbe9a..651dcb5f 100644
--- a/mitogen/select.py
+++ b/mitogen/select.py
@@ -35,12 +35,25 @@ class Error(mitogen.core.Error):
     pass
 
 
+class Event(object):
+    """
+    Represents one selected event.
+    """
+    #: The first Receiver or Latch the event traversed.
+    source = None
+
+    #: The :class:`mitogen.core.Message` delivered to a receiver, or the object
+    #: posted to a latch.
+    data = None
+
+
 class Select(object):
     """
     Support scatter/gather asynchronous calls and waiting on multiple
-    receivers, channels, and sub-Selects. Accepts a sequence of
-    :class:`mitogen.core.Receiver` or :class:`mitogen.select.Select` instances
-    and returns the first value posted to any receiver or select.
+    receivers, channels, latches, and sub-Selects. Accepts a sequence of
+    :class:`mitogen.core.Receiver`, :class:`mitogen.select.Select` or
+    :class:`mitogen.core.Latch` instances and returns the first value posted to
+    any receiver or select.
 
     If `oneshot` is :data:`True`, then remove each receiver as it yields a
     result; since :meth:`__iter__` terminates once the final receiver is
@@ -84,6 +97,19 @@ class Select(object):
 
         for msg in mitogen.select.Select(selects):
             print(msg.unpickle())
+
+    :class:`Select` may be used to mix inter-thread and inter-process IO:
+
+        latch = mitogen.core.Latch()
+        start_thread(latch)
+        recv = remote_host.call_async(os.getuid)
+
+        sel = Select([latch, recv])
+        event = sel.get_event()
+        if event.source is latch:
+            # woken by a local thread
+        else:
+            # woken by function call result
     """
 
     notify = None
@@ -145,14 +171,29 @@ class Select(object):
     def __exit__(self, e_type, e_val, e_tb):
         self.close()
 
-    def __iter__(self):
+    def iter_data(self):
         """
-        Yield the result of :meth:`get` until no receivers remain in the
-        select, either because `oneshot` is :data:`True`, or each receiver was
+        Yield :attr:`Event.data` until no receivers remain in the select,
+        either because `oneshot` is :data:`True`, or each receiver was
         explicitly removed via :meth:`remove`.
+
+        :meth:`__iter__` is an alias for :meth:`iter_data`, allowing loops
+        like::
+
+            for msg in Select([recv1, recv2]):
+                print msg.unpickle()
         """
         while self._receivers:
-            yield self.get()
+            yield self.get_event().data
+
+    __iter__ = iter_data
+
+    def iter_events(self):
+        """
+        Yield :class:`Event` instances until no receivers remain in the select.
+        """
+        while self._receivers:
+            yield self.get_event()
 
     loop_msg = 'Adding this Select instance would create a Select cycle'
 
@@ -170,8 +211,8 @@ class Select(object):
 
     def add(self, recv):
         """
-        Add the :class:`mitogen.core.Receiver` or :class:`Select` `recv` to the
-        select.
+        Add a :class:`mitogen.core.Receiver`, :class:`Select` or
+        :class:`mitogen.core.Latch` to the select.
 
         :raises mitogen.select.Error:
             An attempt was made to add a :class:`Select` to which this select
@@ -193,10 +234,9 @@ class Select(object):
 
     def remove(self, recv):
         """
-        Remove the :class:`mitogen.core.Receiver` or :class:`Select` `recv`
-        from the select. Note that if the receiver has notified prior to
-        :meth:`remove`, it will still be returned by a subsequent :meth:`get`.
-        This may change in a future version.
+        Remove an object from from the select. Note that if the receiver has
+        notified prior to :meth:`remove`, it will still be returned by a
+        subsequent :meth:`get`. This may change in a future version.
         """
         try:
             if recv.notify != self._put:
@@ -239,6 +279,13 @@ class Select(object):
     empty_msg = 'Cannot get(), Select instance is empty'
 
     def get(self, timeout=None, block=True):
+        """
+        Call `get_event(timeout, block)` returning :attr:`Event.data` of the
+        first available event.
+        """
+        return self.get_event(timeout, block).data
+
+    def get_event(self, timeout=None, block=True):
         """
         Fetch the next available value from any receiver, or raise
         :class:`mitogen.core.TimeoutError` if no value is available within
@@ -263,14 +310,21 @@ class Select(object):
         if not self._receivers:
             raise Error(self.empty_msg)
 
+        event = Event()
         while True:
             recv = self._latch.get(timeout=timeout, block=block)
             try:
-                msg = recv.get(block=False)
+                if isinstance(recv, Select):
+                    event = recv.get_event(block=False)
+                else:
+                    event.source = recv
+                    event.data = recv.get(block=False)
                 if self._oneshot:
                     self.remove(recv)
-                msg.receiver = recv
-                return msg
+                if isinstance(recv, mitogen.core.Receiver):
+                    # Remove in 0.3.x.
+                    event.data.receiver = recv
+                return event
             except mitogen.core.TimeoutError:
                 # A receiver may have been queued with no result if another
                 # thread drained it before we woke up, or because another
diff --git a/tests/select_test.py b/tests/select_test.py
index 7e6256c8..f08c9f3a 100644
--- a/tests/select_test.py
+++ b/tests/select_test.py
@@ -9,6 +9,18 @@ import testlib
 class BoolTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.select.Select
 
+    def test_latch(self):
+        latch = mitogen.core.Latch()  # oneshot
+        select = self.klass()
+        self.assertFalse(select)
+        select.add(latch)
+        self.assertTrue(select)
+
+        latch.put(123)
+        self.assertTrue(select)
+        self.assertEquals(123, select.get())
+        self.assertFalse(select)
+
     def test_receiver(self):
         recv = mitogen.core.Receiver(self.router)  # oneshot
         select = self.klass()
@@ -25,6 +37,14 @@ class BoolTest(testlib.RouterMixin, testlib.TestCase):
 class AddTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.select.Select
 
+    def test_latch(self):
+        latch = mitogen.core.Latch()
+        select = self.klass()
+        select.add(latch)
+        self.assertEquals(1, len(select._receivers))
+        self.assertEquals(latch, select._receivers[0])
+        self.assertEquals(select._put, latch.notify)
+
     def test_receiver(self):
         recv = mitogen.core.Receiver(self.router)
         select = self.klass()
@@ -98,14 +118,14 @@ class AddTest(testlib.RouterMixin, testlib.TestCase):
 class RemoveTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.select.Select
 
-    def test_empty(self):
+    def test_receiver_empty(self):
         select = self.klass()
         recv = mitogen.core.Receiver(self.router)
         exc = self.assertRaises(mitogen.select.Error,
             lambda: select.remove(recv))
         self.assertEquals(str(exc), self.klass.not_present_msg)
 
-    def test_absent(self):
+    def test_receiver_absent(self):
         select = self.klass()
         recv = mitogen.core.Receiver(self.router)
         recv2 = mitogen.core.Receiver(self.router)
@@ -114,7 +134,7 @@ class RemoveTest(testlib.RouterMixin, testlib.TestCase):
             lambda: select.remove(recv))
         self.assertEquals(str(exc), self.klass.not_present_msg)
 
-    def test_present(self):
+    def test_receiver_present(self):
         select = self.klass()
         recv = mitogen.core.Receiver(self.router)
         select.add(recv)
@@ -122,6 +142,30 @@ class RemoveTest(testlib.RouterMixin, testlib.TestCase):
         self.assertEquals(0, len(select._receivers))
         self.assertEquals(None, recv.notify)
 
+    def test_latch_empty(self):
+        select = self.klass()
+        latch = mitogen.core.Latch()
+        exc = self.assertRaises(mitogen.select.Error,
+            lambda: select.remove(latch))
+        self.assertEquals(str(exc), self.klass.not_present_msg)
+
+    def test_latch_absent(self):
+        select = self.klass()
+        latch = mitogen.core.Latch()
+        latch2 = mitogen.core.Latch()
+        select.add(latch2)
+        exc = self.assertRaises(mitogen.select.Error,
+            lambda: select.remove(latch))
+        self.assertEquals(str(exc), self.klass.not_present_msg)
+
+    def test_latch_present(self):
+        select = self.klass()
+        latch = mitogen.core.Latch()
+        select.add(latch)
+        select.remove(latch)
+        self.assertEquals(0, len(select._receivers))
+        self.assertEquals(None, latch.notify)
+
 
 class CloseTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.select.Select
@@ -130,6 +174,18 @@ class CloseTest(testlib.RouterMixin, testlib.TestCase):
         select = self.klass()
         select.close()  # No effect.
 
+    def test_one_latch(self):
+        select = self.klass()
+        latch = mitogen.core.Latch()
+        select.add(latch)
+
+        self.assertEquals(1, len(select._receivers))
+        self.assertEquals(select._put, latch.notify)
+
+        select.close()
+        self.assertEquals(0, len(select._receivers))
+        self.assertEquals(None, latch.notify)
+
     def test_one_receiver(self):
         select = self.klass()
         recv = mitogen.core.Receiver(self.router)
@@ -174,18 +230,35 @@ class EmptyTest(testlib.RouterMixin, testlib.TestCase):
         select = self.klass([recv])
         self.assertTrue(select.empty())
 
-    def test_nonempty_before_add(self):
+    def test_nonempty_receiver_before_add(self):
         recv = mitogen.core.Receiver(self.router)
         recv._on_receive(mitogen.core.Message.pickled('123'))
         select = self.klass([recv])
         self.assertFalse(select.empty())
 
-    def test_nonempty_after_add(self):
+    def test_nonempty__receiver_after_add(self):
         recv = mitogen.core.Receiver(self.router)
         select = self.klass([recv])
         recv._on_receive(mitogen.core.Message.pickled('123'))
         self.assertFalse(select.empty())
 
+    def test_empty_latch(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch])
+        self.assertTrue(select.empty())
+
+    def test_nonempty_latch_before_add(self):
+        latch = mitogen.core.Latch()
+        latch.put(123)
+        select = self.klass([latch])
+        self.assertFalse(select.empty())
+
+    def test_nonempty__latch_after_add(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch])
+        latch.put(123)
+        self.assertFalse(select.empty())
+
 
 class IterTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.select.Select
@@ -194,18 +267,24 @@ class IterTest(testlib.RouterMixin, testlib.TestCase):
         select = self.klass()
         self.assertEquals([], list(select))
 
-    def test_nonempty(self):
+    def test_nonempty_receiver(self):
         recv = mitogen.core.Receiver(self.router)
         select = self.klass([recv])
         msg = mitogen.core.Message.pickled('123')
         recv._on_receive(msg)
         self.assertEquals([msg], list(select))
 
+    def test_nonempty_latch(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch])
+        latch.put(123)
+        self.assertEquals([123], list(select))
+
 
 class OneShotTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.select.Select
 
-    def test_true_removed_after_get(self):
+    def test_true_receiver_removed_after_get(self):
         recv = mitogen.core.Receiver(self.router)
         select = self.klass([recv])
         msg = mitogen.core.Message.pickled('123')
@@ -215,7 +294,7 @@ class OneShotTest(testlib.RouterMixin, testlib.TestCase):
         self.assertEquals(0, len(select._receivers))
         self.assertEquals(None, recv.notify)
 
-    def test_false_persists_after_get(self):
+    def test_false_receiver_persists_after_get(self):
         recv = mitogen.core.Receiver(self.router)
         select = self.klass([recv], oneshot=False)
         msg = mitogen.core.Message.pickled('123')
@@ -226,8 +305,26 @@ class OneShotTest(testlib.RouterMixin, testlib.TestCase):
         self.assertEquals(recv, select._receivers[0])
         self.assertEquals(select._put, recv.notify)
 
+    def test_true_latch_removed_after_get(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch])
+        latch.put(123)
+        self.assertEquals(123, select.get())
+        self.assertEquals(0, len(select._receivers))
+        self.assertEquals(None, latch.notify)
 
-class GetTest(testlib.RouterMixin, testlib.TestCase):
+    def test_false_latch_persists_after_get(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch], oneshot=False)
+        latch.put(123)
+
+        self.assertEquals(123, select.get())
+        self.assertEquals(1, len(select._receivers))
+        self.assertEquals(latch, select._receivers[0])
+        self.assertEquals(select._put, latch.notify)
+
+
+class GetReceiverTest(testlib.RouterMixin, testlib.TestCase):
     klass = mitogen.select.Select
 
     def test_no_receivers(self):
@@ -285,5 +382,79 @@ class GetTest(testlib.RouterMixin, testlib.TestCase):
             lambda: select.get(timeout=0.0))
 
 
+class GetLatchTest(testlib.RouterMixin, testlib.TestCase):
+    klass = mitogen.select.Select
+
+    def test_no_latches(self):
+        select = self.klass()
+        exc = self.assertRaises(mitogen.select.Error,
+            lambda: select.get())
+        self.assertEquals(str(exc), self.klass.empty_msg)
+
+    def test_timeout_no_receivers(self):
+        select = self.klass()
+        exc = self.assertRaises(mitogen.select.Error,
+            lambda: select.get(timeout=1.0))
+        self.assertEquals(str(exc), self.klass.empty_msg)
+
+    def test_zero_timeout(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch])
+        self.assertRaises(mitogen.core.TimeoutError,
+            lambda: select.get(timeout=0.0))
+
+    def test_timeout(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch])
+        self.assertRaises(mitogen.core.TimeoutError,
+            lambda: select.get(timeout=0.1))
+
+    def test_nonempty_before_add(self):
+        latch = mitogen.core.Latch()
+        latch.put(123)
+        select = self.klass([latch])
+        self.assertEquals(123, select.get())
+
+    def test_nonempty_after_add(self):
+        latch = mitogen.core.Latch()
+        select = self.klass([latch])
+        latch.put(123)
+        self.assertEquals(123, latch.get())
+
+    def test_drained_by_other_thread(self):
+        latch = mitogen.core.Latch()
+        latch.put(123)
+        select = self.klass([latch])
+        self.assertEquals(123, latch.get())
+        self.assertRaises(mitogen.core.TimeoutError,
+            lambda: select.get(timeout=0.0))
+
+
+class GetEventTest(testlib.RouterMixin, testlib.TestCase):
+    klass = mitogen.select.Select
+
+    def test_empty(self):
+        select = self.klass()
+        exc = self.assertRaises(mitogen.select.Error,
+            lambda: select.get())
+        self.assertEquals(str(exc), self.klass.empty_msg)
+
+    def test_latch(self):
+        latch = mitogen.core.Latch()
+        latch.put(123)
+        select = self.klass([latch])
+        event = select.get_event()
+        self.assertEquals(latch, event.source)
+        self.assertEquals(123, event.data)
+
+    def test_receiver(self):
+        recv = mitogen.core.Receiver(self.router)
+        recv._on_receive(mitogen.core.Message.pickled('123'))
+        select = self.klass([recv])
+        event = select.get_event()
+        self.assertEquals(recv, event.source)
+        self.assertEquals('123', event.data.unpickle())
+
+
 if __name__ == '__main__':
     unittest2.main()

From 28aa8b3b278c173163cf68b6781f5059deedc182 Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 01:44:46 +0000
Subject: [PATCH 02/10] issue #535: docs: update Changelog.

---
 docs/changelog.rst | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 157ed902..8a01c033 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -151,6 +151,11 @@ Core Library
 * `ca63c26e <https://github.com/dw/mitogen/commit/ca63c26e>`_:
   :meth:`mitogen.core.Latch.put`'s `obj` argument was made optional.
 
+* `2c921fea <https://github.com/dw/mitogen/commit/2c921fea>`_: to support
+  function calls on a service pool from another thread,
+  :class:`mitogen.select.Select` additionally permits waiting on
+  :class:`mitogen.core.Latch`.
+
 
 Thanks!
 ~~~~~~~

From 72862f0bb90dbc45988b1c135f181d07a37d415d Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 04:49:51 +0000
Subject: [PATCH 03/10] issue #535: docs: fix up Select doc

---
 docs/api.rst      |  4 ++++
 mitogen/select.py | 12 ++++++------
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/docs/api.rst b/docs/api.rst
index 3fd70bea..2502766f 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -579,6 +579,10 @@ Select Class
 
 .. module:: mitogen.select
 .. currentmodule:: mitogen.select
+
+.. autoclass:: Event
+    :members:
+
 .. autoclass:: Select
     :members:
 
diff --git a/mitogen/select.py b/mitogen/select.py
index 651dcb5f..51aebc22 100644
--- a/mitogen/select.py
+++ b/mitogen/select.py
@@ -50,10 +50,10 @@ class Event(object):
 class Select(object):
     """
     Support scatter/gather asynchronous calls and waiting on multiple
-    receivers, channels, latches, and sub-Selects. Accepts a sequence of
-    :class:`mitogen.core.Receiver`, :class:`mitogen.select.Select` or
-    :class:`mitogen.core.Latch` instances and returns the first value posted to
-    any receiver or select.
+    :class:`receivers <mitogen.core.Receiver>`,
+    :class:`channels <mitogen.core.Channel>`,
+    :class:`latches <mitogen.core.Latch>`, and
+    :class:`sub-selects <Select>`.
 
     If `oneshot` is :data:`True`, then remove each receiver as it yields a
     result; since :meth:`__iter__` terminates once the final receiver is
@@ -287,7 +287,7 @@ class Select(object):
 
     def get_event(self, timeout=None, block=True):
         """
-        Fetch the next available value from any receiver, or raise
+        Fetch the next available :class:`Event` from any source, or raise
         :class:`mitogen.core.TimeoutError` if no value is available within
         `timeout` seconds.
 
@@ -300,7 +300,7 @@ class Select(object):
             If :data:`False`, immediately raise
             :class:`mitogen.core.TimeoutError` if the select is empty.
         :return:
-            :class:`mitogen.core.Message`
+            :class:`Event`.
         :raises mitogen.core.TimeoutError:
             Timeout was reached.
         :raises mitogen.core.LatchError:

From eb9ec26622be1f4e1959ebc1d0c04d10ea1f5873 Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 21:46:47 +0000
Subject: [PATCH 04/10] issue #535: core: unicode.encode() may take importer
 lock on 2.x

Found on Python 2.4, where import happens immediately following connect.

- Main thread executes import statement, triggers request to parent
- Broker thread attempts to deliver request via Router
- Router discovers parent has disconnected, prepares a dead message
- .dead() calls unicode.encode() to format reason string
- .encode() attemptsto import a codec module
- deadlock

----

(gdb) pystack
/usr/local/python2.4.6/lib/python2.4/encodings/__init__.py (69): search_function
<stdin> (733): dead
<stdin> (2717): _maybe_send_dead
<stdin> (2724): _invoke
<stdin> (2749): _async_route
<stdin> (1635): _receive_one
<stdin> (1603): _internal_receive
<stdin> (1613): on_receive
<stdin> (2931): _call
<stdin> (2942): _loop_once
<stdin> (2988): _do_broker_main
<stdin> (545): _profile_hook
<stdin> (3007): _broker_main
/usr/local/python2.4.6/lib/python2.4/threading.py (420): run
/usr/local/python2.4.6/lib/python2.4/threading.py (424): __bootstrap
---
 mitogen/core.py | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/mitogen/core.py b/mitogen/core.py
index 6bca1b1a..d8e3fdb6 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -103,6 +103,9 @@ IOLOG = logging.getLogger('mitogen.io')
 IOLOG.setLevel(logging.INFO)
 
 LATIN1_CODEC = encodings.latin_1.Codec()
+# str.encode() may take import lock. Deadlock possible if broker calls
+# .encode() on behalf of thread currently waiting for module.
+UTF8_CODEC = encodings.latin_1.Codec()
 
 _v = False
 _vv = False
@@ -271,9 +274,8 @@ class Kwargs(dict):
         def __init__(self, dct):
             for k, v in dct.iteritems():
                 if type(k) is unicode:
-                    self[k.encode()] = v
-                else:
-                    self[k] = v
+                    k, _ = UTF8_CODEC.encode(k)
+                self[k] = v
 
     def __repr__(self):
         return 'Kwargs(%s)' % (dict.__repr__(self),)
@@ -735,7 +737,7 @@ class Message(object):
         """
         Syntax helper to construct a dead message.
         """
-        kwargs['data'] = (reason or u'').encode()
+        kwargs['data'], _ = UTF8_CODEC.encode(reason or u'')
         return cls(reply_to=IS_DEAD, **kwargs)
 
     @classmethod
@@ -1332,7 +1334,7 @@ class Importer(object):
 
         if mod.__package__ and not PY3:
             # 2.x requires __package__ to be exactly a string.
-            mod.__package__ = mod.__package__.encode()
+            mod.__package__, _ = UTF8_CODEC.encode(mod.__package__)
 
         source = self.get_source(fullname)
         try:

From 514d35fd10ccc72ad583f0b1267e2110b8ef013f Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 21:50:44 +0000
Subject: [PATCH 05/10] issue #535: service: support Pool.defer() like
 Broker.defer()

---
 mitogen/service.py | 36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/mitogen/service.py b/mitogen/service.py
index 3254e69a..6f50275d 100644
--- a/mitogen/service.py
+++ b/mitogen/service.py
@@ -411,10 +411,12 @@ class Service(object):
     def __repr__(self):
         return '%s()' % (self.__class__.__name__,)
 
-    def on_message(self, recv, msg):
+    def on_message(self, event):
         """
         Called when a message arrives on any of :attr:`select`'s registered
         receivers.
+
+        :param mitogen.select.Event event:
         """
         pass
 
@@ -452,6 +454,7 @@ class Pool(object):
     def __init__(self, router, services, size=1, overwrite=False):
         self.router = router
         self._activator = self.activator_class()
+        self._ipc_latch = mitogen.core.Latch()
         self._receiver = mitogen.core.Receiver(
             router=router,
             handle=mitogen.core.CALL_SERVICE,
@@ -460,9 +463,13 @@ class Pool(object):
 
         self._select = mitogen.select.Select(oneshot=False)
         self._select.add(self._receiver)
+        self._select.add(self._ipc_latch)
         #: Serialize service construction.
         self._lock = threading.Lock()
-        self._func_by_recv = {self._receiver: self._on_service_call}
+        self._func_by_source = {
+            self._receiver: self._on_service_call,
+            self._ipc_latch: self._on_ipc_latch,
+        }
         self._invoker_by_name = {}
 
         for service in services:
@@ -488,10 +495,10 @@ class Pool(object):
         name = service.name()
         if name in self._invoker_by_name:
             raise Error('service named %r already registered' % (name,))
-        assert service.select not in self._func_by_recv
+        assert service.select not in self._func_by_source
         invoker = service.invoker_class(service=service)
         self._invoker_by_name[name] = invoker
-        self._func_by_recv[service.select] = service.on_message
+        self._func_by_source[service.select] = service.on_message
 
     closed = False
 
@@ -534,7 +541,18 @@ class Pool(object):
                 isinstance(tup[2], dict)):
             raise mitogen.core.CallError('Invalid message format.')
 
-    def _on_service_call(self, recv, msg):
+    def defer(self, func, *args, **kwargs):
+        """
+        Arrange for `func(*args, **kwargs)` to be invoked in the context of a
+        service pool thread.
+        """
+        self._ipc_latch.put(lambda: func(*args, **kwargs))
+
+    def _on_ipc_latch(self, event):
+        event.data()
+
+    def _on_service_call(self, event):
+        msg = event.data
         service_name = None
         method_name = None
         try:
@@ -555,17 +573,17 @@ class Pool(object):
     def _worker_run(self):
         while not self.closed:
             try:
-                msg = self._select.get()
+                event = self._select.get_event()
             except (mitogen.core.ChannelError, mitogen.core.LatchError):
                 e = sys.exc_info()[1]
                 LOG.debug('%r: channel or latch closed, exitting: %s', self, e)
                 return
 
-            func = self._func_by_recv[msg.receiver]
+            func = self._func_by_source[event.source]
             try:
-                func(msg.receiver, msg)
+                func(event)
             except Exception:
-                LOG.exception('While handling %r using %r', msg, func)
+                LOG.exception('While handling %r using %r', event.data, func)
 
     def _worker_main(self):
         try:

From c119ae8f6613eb021e6240580a11669a6f34e983 Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 21:50:44 +0000
Subject: [PATCH 06/10] issue #535: docs: update Changelog

---
 docs/changelog.rst | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 8a01c033..cd46380c 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -148,13 +148,17 @@ Fixes
 Core Library
 ~~~~~~~~~~~~
 
+* `#535 <https://github.com/dw/mitogen/issues/535>`_: to support function calls
+  on a service pool from another thread, :class:`mitogen.select.Select`
+  additionally permits waiting on :class:`mitogen.core.Latch`.
+
+* `#535 <https://github.com/dw/mitogen/issues/535>`_:
+  :class:`mitogen.service.Pool.defer` allows any function to be enqueued for
+  the thread pool from another thread.
+
 * `ca63c26e <https://github.com/dw/mitogen/commit/ca63c26e>`_:
   :meth:`mitogen.core.Latch.put`'s `obj` argument was made optional.
 
-* `2c921fea <https://github.com/dw/mitogen/commit/2c921fea>`_: to support
-  function calls on a service pool from another thread,
-  :class:`mitogen.select.Select` additionally permits waiting on
-  :class:`mitogen.core.Latch`.
 
 
 Thanks!

From 63f4864b217c378671935a5a68896d5ceac46d33 Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 21:55:14 +0000
Subject: [PATCH 07/10] issue #535: introduce mitogen.os_fork module and Corker
 class.

---
 docs/api.rst       |   8 +++
 mitogen/core.py    |   1 +
 mitogen/os_fork.py | 153 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 162 insertions(+)
 create mode 100644 mitogen/os_fork.py

diff --git a/docs/api.rst b/docs/api.rst
index 2502766f..6add0568 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -609,6 +609,14 @@ Broker Class
    :members:
 
 
+Corker Class
+============
+
+.. currentmodule:: mitogen.os_fork
+.. autoclass:: Corker
+   :members:
+
+
 Utility Functions
 =================
 
diff --git a/mitogen/core.py b/mitogen/core.py
index d8e3fdb6..4b8565ca 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -1094,6 +1094,7 @@ class Importer(object):
         'lxd',
         'master',
         'minify',
+        'os_fork',
         'parent',
         'select',
         'service',
diff --git a/mitogen/os_fork.py b/mitogen/os_fork.py
new file mode 100644
index 00000000..2b74bdfc
--- /dev/null
+++ b/mitogen/os_fork.py
@@ -0,0 +1,153 @@
+# Copyright 2019, David Wilson
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice,
+# this list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice,
+# this list of conditions and the following disclaimer in the documentation
+# and/or other materials provided with the distribution.
+#
+# 3. Neither the name of the copyright holder nor the names of its contributors
+# may be used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+
+# !mitogen: minify_safe
+
+"""
+When operating in a mixed threading/forking environment, it is critical no
+threads are active at the moment of fork, as they could be within critical
+sections whose mutexes are snapshotted in the locked state in the fork child.
+
+To permit unbridled Mitogen use in a forking program, a mechanism must exist to
+temporarily halt any threads in operation -- namely the broker and any pool
+threads.
+"""
+
+import os
+import socket
+import sys
+import weakref
+
+import mitogen.core
+
+
+# List of weakrefs. On Python 2.4, mitogen.core registers its Broker on this
+# list and mitogen.service registers its Pool too.
+_brokers = weakref.WeakValueDictionary()
+_pools = weakref.WeakValueDictionary()
+
+
+def _notice_broker_or_pool(obj):
+    if isinstance(obj, mitogen.core.Broker):
+        _brokers[id(obj)] = obj
+    else:
+        _pools[id(obj)] = obj
+
+
+def wrap_os__fork():
+    corker = Corker(
+        brokers=list(_brokers.values()),
+        pools=list(_pools.values()),
+    )
+    try:
+        corker.cork()
+        return os__fork()
+    finally:
+        corker.uncork()
+
+
+# If Python 2.4/2.5 where threading state is not fixed up, subprocess.Popen()
+# may still deadlock due to the broker thread. In this case, pause os.fork() so
+# that all active threads are paused during fork.
+if sys.version_info < (2, 6):
+    os__fork = os.fork
+    os.fork = wrap_os__fork
+
+
+class Corker(object):
+    """
+    Arrange for :class:`mitogen.core.Broker` and optionally
+    :class:`mitogen.service.Pool` to be temporarily "corked" while fork
+    operations may occur.
+
+    Since this necessarily involves posting a message to every existent thread
+    and verifying acknowledgement, it will never be a fast operation.
+    """
+    def __init__(self, brokers=(), pools=()):
+        self.brokers = brokers
+        self.pools = pools
+
+    def _do_cork(self, s, wsock):
+        try:
+            try:
+                while True:
+                    # at least EINTR is possible. Do our best to keep handling
+                    # outside the GIL in this case using sendall().
+                    wsock.sendall(s)
+            except socket.error:
+                pass
+        finally:
+            wsock.close()
+
+    def _cork_one(self, s, obj):
+        """
+        To ensure the target thread has all locks dropped, we ask it to write a
+        large string to a socket with a small buffer that has O_NONBLOCK
+        disabled. CPython will drop the GIL and enter the write() system call,
+        where it will block until the socket buffer is drained, or the write
+        side is closed. We can detect the thread has blocked outside of Python
+        code by checking if the socket buffer has started to fill using a
+        poller.
+        """
+        rsock, wsock = mitogen.parent.create_socketpair(size=4096)
+        mitogen.core.set_cloexec(rsock.fileno())
+        mitogen.core.set_cloexec(wsock.fileno())
+        mitogen.core.set_block(wsock)  # gevent
+        self._rsocks.append(rsock)
+        obj.defer(self._do_cork, s, wsock)
+        poller = mitogen.core.Poller()
+        poller.start_receive(rsock.fileno())
+        try:
+            while True:
+                for fd in poller.poll():
+                    return
+        finally:
+            poller.close()
+
+    def cork(self):
+        """
+        Arrange for the broker and optional pool to be paused with no locks
+        held. This will not return until each thread acknowledges it has ceased
+        execution.
+        """
+        s = 'CORK' * ((128 / 4) * 1024)
+        self._rsocks = []
+        for pool in self.pools:
+            if not pool.closed:
+                for x in range(pool.size):
+                    self._cork_one(s, pool)
+        for broker in self.brokers:
+            if broker._alive:
+                self._cork_one(s, broker)
+
+    def uncork(self):
+        """
+        Arrange for paused threads to resume operation.
+        """
+        for rsock in self._rsocks:
+            rsock.close()

From c1d73e1f4f7d7442826e02d9a5f51915d4d4ec40 Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 21:55:14 +0000
Subject: [PATCH 08/10] issue #535: parent: add create_socketpair(size=..)
 parameter.

---
 mitogen/parent.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mitogen/parent.py b/mitogen/parent.py
index f793f234..f25bd6c2 100644
--- a/mitogen/parent.py
+++ b/mitogen/parent.py
@@ -253,7 +253,7 @@ def close_nonstandard_fds():
             pass
 
 
-def create_socketpair():
+def create_socketpair(size=None):
     """
     Create a :func:`socket.socketpair` to use for use as a child process's UNIX
     stdio channels. As socket pairs are bidirectional, they are economical on
@@ -265,10 +265,10 @@ def create_socketpair():
     parentfp, childfp = socket.socketpair()
     parentfp.setsockopt(socket.SOL_SOCKET,
                         socket.SO_SNDBUF,
-                        mitogen.core.CHUNK_SIZE)
+                        size or mitogen.core.CHUNK_SIZE)
     childfp.setsockopt(socket.SOL_SOCKET,
                        socket.SO_RCVBUF,
-                       mitogen.core.CHUNK_SIZE)
+                       size or mitogen.core.CHUNK_SIZE)
     return parentfp, childfp
 
 

From 06e52ca89f48d257059b1889bb1029b84500fa4d Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 21:55:14 +0000
Subject: [PATCH 09/10] issue #535: wire mitogen.os_fork into Broker and Pool.

---
 mitogen/core.py         | 12 ++++++++++++
 mitogen/service.py      |  8 ++++++++
 tests/responder_test.py | 15 +++++++++------
 3 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/mitogen/core.py b/mitogen/core.py
index 4b8565ca..4b3df595 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -3348,6 +3348,17 @@ class ExternalContext(object):
         # Reopen with line buffering.
         sys.stdout = os.fdopen(1, 'w', 1)
 
+    def _py24_25_compat(self):
+        """
+        Python 2.4/2.5 have grave difficulties with threads/fork. We
+        mandatorily quiesce all running threads during fork using a
+        monkey-patch there.
+        """
+        if sys.version_info < (2, 6):
+            # import_module() is used to avoid dep scanner.
+            os_fork = import_module('mitogen.os_fork')
+            mitogen.os_fork._notice_broker_or_pool(self.broker)
+
     def main(self):
         self._setup_master()
         try:
@@ -3375,6 +3386,7 @@ class ExternalContext(object):
                                  socket.gethostname())
                 _v and LOG.debug('Recovered sys.executable: %r', sys.executable)
 
+                self._py24_25_compat()
                 self.dispatcher.run()
                 _v and LOG.debug('ExternalContext.main() normal exit')
             except KeyboardInterrupt:
diff --git a/mitogen/service.py b/mitogen/service.py
index 6f50275d..dc200b95 100644
--- a/mitogen/service.py
+++ b/mitogen/service.py
@@ -474,6 +474,7 @@ class Pool(object):
 
         for service in services:
             self.add(service)
+        self._py_24_25_compat()
         self._threads = []
         for x in range(size):
             name = 'mitogen.service.Pool.%x.worker-%d' % (id(self), x,)
@@ -487,6 +488,13 @@ class Pool(object):
 
         LOG.debug('%r: initialized', self)
 
+    def _py_24_25_compat(self):
+        if sys.version_info < (2, 6):
+            # import_module() is used to avoid dep scanner sending mitogen.fork
+            # to all mitogen.service importers.
+            os_fork = mitogen.core.import_module('mitogen.os_fork')
+            os_fork._notice_broker_or_pool(self)
+
     @property
     def size(self):
         return len(self._threads)
diff --git a/tests/responder_test.py b/tests/responder_test.py
index da4f22d7..dbc68a3c 100644
--- a/tests/responder_test.py
+++ b/tests/responder_test.py
@@ -74,8 +74,9 @@ class GoodModulesTest(testlib.RouterMixin, testlib.TestCase):
         context = self.router.local()
 
         self.assertEquals(256, context.call(plain_old_module.pow, 2, 8))
-        self.assertEquals(1, self.router.responder.get_module_count)
-        self.assertEquals(1, self.router.responder.good_load_module_count)
+        os_fork = int(sys.version_info < (2, 6))  # mitogen.os_fork
+        self.assertEquals(1+os_fork, self.router.responder.get_module_count)
+        self.assertEquals(1+os_fork, self.router.responder.good_load_module_count)
         self.assertLess(300, self.router.responder.good_load_module_size)
 
     def test_simple_pkg(self):
@@ -84,8 +85,9 @@ class GoodModulesTest(testlib.RouterMixin, testlib.TestCase):
         context = self.router.local()
         self.assertEquals(3,
             context.call(simple_pkg.a.subtract_one_add_two, 2))
-        self.assertEquals(2, self.router.responder.get_module_count)
-        self.assertEquals(3, self.router.responder.good_load_module_count)
+        os_fork = int(sys.version_info < (2, 6))  # mitogen.os_fork
+        self.assertEquals(2+os_fork, self.router.responder.get_module_count)
+        self.assertEquals(3+os_fork, self.router.responder.good_load_module_count)
         self.assertEquals(0, self.router.responder.bad_load_module_count)
         self.assertLess(450, self.router.responder.good_load_module_size)
 
@@ -185,9 +187,10 @@ class ForwardTest(testlib.RouterMixin, testlib.TestCase):
         c1 = self.router.local()
         c2 = self.router.local(via=c1)
 
+        os_fork = int(sys.version_info < (2, 6))
         self.assertEquals(256, c2.call(plain_old_module.pow, 2, 8))
-        self.assertEquals(2, self.router.responder.get_module_count)
-        self.assertEquals(2, self.router.responder.good_load_module_count)
+        self.assertEquals(2+os_fork, self.router.responder.get_module_count)
+        self.assertEquals(2+os_fork, self.router.responder.good_load_module_count)
         self.assertLess(10000, self.router.responder.good_load_module_size)
         self.assertGreater(40000, self.router.responder.good_load_module_size)
 

From ebbf5ab62ca129ce6a3c71757a1dd43afe7493bd Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sun, 17 Feb 2019 21:55:14 +0000
Subject: [PATCH 10/10] issue #535: update Changelog.

---
 docs/changelog.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index cd46380c..02d2495c 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -156,6 +156,13 @@ Core Library
   :class:`mitogen.service.Pool.defer` allows any function to be enqueued for
   the thread pool from another thread.
 
+* `#535 <https://github.com/dw/mitogen/issues/535>`_: a new
+  :mod:`mitogen.os_fork` module provides a :func:`os.fork` wrapper that pauses
+  all thread activity during a fork. :class:`mitogen.core.Broker` and
+  :class:`mitogen.service.Pool` automatically record their existence so that an
+  :func:`os.fork` monkey-patch activated for Python 2.4 and 2.5 can
+  automatically pause them for any attempt to start a subprocess.
+
 * `ca63c26e <https://github.com/dw/mitogen/commit/ca63c26e>`_:
   :meth:`mitogen.core.Latch.put`'s `obj` argument was made optional.