Have slaves close their own CALL_FUNCTION channel on broker shutdown

Necessary when parent stream goes away -- nothing exists to wake up main
thread.

econtext/core.py

@@ -224,6 +224,9 @@ class Receiver(object):
         IOLOG.debug('%r._on_receive(%r)', self, msg)
         self._queue.put(msg)
 
+    def close(self):
+        self._queue.put(_DEAD)
+
     def get(self, timeout=None):
         """Receive an object, or ``None`` if `timeout` is reached."""
         IOLOG.debug('%r.on_receive(timeout=%r)', self, timeout)
@@ -1029,6 +1032,9 @@ class ExternalContext(object):
 
         The :py:class:`IoLogger` connected to ``stderr``.
     """
+    def _on_broker_shutdown(self):
+        self.channel.close()
+
     def _setup_master(self, parent_id, context_id, key, in_fd, out_fd):
         self.broker = Broker()
         self.router = Router(self.broker)
@@ -1044,6 +1050,8 @@ class ExternalContext(object):
         self.stream.accept(in_fd, out_fd)
         self.stream.receive_side.keep_alive = False
 
+        listen(self.broker, 'shutdown', self._on_broker_shutdown)
+
         os.close(in_fd)
         try:
             os.wait()  # Reap first stage.