Handle PEP 475 fallout.

Closes #255

As of Python 3.5, PEP 475 gets in our way.  Runners with long time.sleep()'s
in their _snooze() method (e.g. the retry runner) will have their system call
implemented time.sleep() automatically retried at the C layer.  The only
reliable way to prevent this is to raise an exception in the signal handler.
The standard run() method automatically suppresses this exception, meaning,
it's caught and ignored, but effectively breaks the run() loop, which is just
what we want.

The lmtp and rest runners implement their own run loops, so they also have to
handle this exception, by ignoring it.

2 files changed, 13 insertions, 6 deletions

diff --git a/src/mailman/runners/lmtp.py b/src/mailman/runners/lmtp.py
index b5c7bbb1f..f24107bd7 100644
--- a/src/mailman/runners/lmtp.py
+++ b/src/mailman/runners/lmtp.py
@@ -40,12 +40,14 @@ import logging
 
 from aiosmtpd.controller import Controller
 from aiosmtpd.lmtp import LMTP
+from contextlib import suppress
 from email.utils import parseaddr
 from mailman.config import config
 from mailman.core.runner import Runner
 from mailman.database.transaction import transactional
 from mailman.email.message import Message
 from mailman.interfaces.listmanager import IListManager
+from mailman.interfaces.runner import RunnerInterrupt
 from mailman.utilities.datetime import now
 from mailman.utilities.email import add_message_hash
 from public import public
@@ -240,7 +242,8 @@ class LMTPRunner(Runner):
 
     def run(self):
         """See `IRunner`."""
-        self.lmtp.start()
-        while not self._stop:
-            self._snooze(0)
-        self.lmtp.stop()
+        with suppress(RunnerInterrupt):
+            self.lmtp.start()
+            while not self._stop:
+                self._snooze(0)
+            self.lmtp.stop()
diff --git a/src/mailman/runners/rest.py b/src/mailman/runners/rest.py
index a93d164c1..7758972ed 100644
--- a/src/mailman/runners/rest.py
+++ b/src/mailman/runners/rest.py
@@ -21,7 +21,9 @@ import signal
 import logging
 import threading
 
+from contextlib import suppress
 from mailman.core.runner import Runner
+from mailman.interfaces.runner import RunnerInterrupt
 from mailman.rest.wsgiapp import make_server
 from public import public
 
@@ -59,10 +61,12 @@ class RESTRunner(Runner):
 
     def run(self):
         """See `IRunner`."""
-        self._server.serve_forever()
+        with suppress(RunnerInterrupt):
+            self._server.serve_forever()
 
     def signal_handler(self, signum, frame):
-        super().signal_handler(signum, frame)
+        with suppress(RunnerInterrupt):
+            super().signal_handler(signum, frame)
         if signum in (signal.SIGTERM, signal.SIGINT, signal.SIGUSR1):
             # Set the flag that will terminate the TCPserver loop.
             self._event.set()