publish IOPub from a background thread

removes need to call `sys.stdout.flush` during blocking loops
for backward-compatibility, a BackgroundSocket is passed around that transparently sends messages via the IOPub thread.

Author: minrk

ipykernel/inprocess/iostream.py

@@ -0,0 +1,17 @@
+"""inprocess OutStream subclass"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+from .. import iostream
+
+class OutStream(iostream.OutStream):
+    def __init__(self, session, pub_thread, name, pipe=False):
+        pub_thread.io_loop = None
+        super(OutStream, self).__init__(session, pub_thread, name)
+    
+    def _schedule_flush(self):
+        self.flush()
+
+    def flush(self):
+        self._flush()

ipykernel/inprocess/ipkernel.py

@@ -14,6 +14,7 @@
 from ipykernel.zmqshell import ZMQInteractiveShell
 
 from .socket import DummySocket
+from .iostream import OutStream
 
 #-----------------------------------------------------------------------------
 # Main kernel class
@@ -128,12 +129,10 @@ def _shell_class_default(self):
         return InProcessInteractiveShell
 
     def _stdout_default(self):
-        from ipykernel.iostream import OutStream
-        return OutStream(self.session, self.iopub_socket, u'stdout', pipe=False)
+        return OutStream(self.session, self.iopub_socket, u'stdout')
 
     def _stderr_default(self):
-        from ipykernel.iostream import OutStream
-        return OutStream(self.session, self.iopub_socket, u'stderr', pipe=False)
+        return OutStream(self.session, self.iopub_socket, u'stderr')
 
 #-----------------------------------------------------------------------------
 # Interactive shell subclass