From 9300f847e13784ea0a35ef3d1e05563fef08adfd 2013-02-04 05:12:03
From: Piti Ongmongkolkul <piti118@gmail.com>
Date: 2013-02-04 05:12:03
Subject: [PATCH] Dual buffer with automatic switch. No performance hit for single process.

---

diff --git a/IPython/kernel/zmq/iostream.py b/IPython/kernel/zmq/iostream.py
index 83505d6..46dc7f8 100644
--- a/IPython/kernel/zmq/iostream.py
+++ b/IPython/kernel/zmq/iostream.py
@@ -1,5 +1,6 @@
 import sys
 import time
+import os
 from io import StringIO
 
 from session import extract_header, Message
@@ -7,6 +8,9 @@ from session import extract_header, Message
 from IPython.utils import io, text
 from IPython.utils import py3compat
 
+import multiprocessing as mp
+import multiprocessing.sharedctypes as mpshc
+from ctypes import c_bool
 #-----------------------------------------------------------------------------
 # Globals
 #-----------------------------------------------------------------------------
@@ -29,6 +33,46 @@ class OutStream(object):
         self.name = name
         self.parent_header = {}
         self._new_buffer()
+        self._manager = mp.Manager()
+        #use sharectype here so it don't have to hit the manager
+        #no synchronize needed either(right?). Just a flag telling the master
+        #to switch the buffer to que
+        self._found_newprocess = mpshc.RawValue(c_bool, False)
+        self._que_buffer = self._manager.Queue()
+        self._que_lock = self._manager.Lock()
+        self._masterpid = os.getpid()
+        self._master_has_switched = False
+
+    def _switch_to_que(self):
+        #should only be called on master process
+        #don't clear the que before putting data in since
+        #child process might have put something in the que before the
+        #master know it.
+        self._que_buffer.put(self._buffer.getvalue())
+        self._new_buffer()
+        self._start = -1
+
+    def _is_master_process(self):
+        return os.getpid()==self._masterpid
+
+    def _debug_print(self,s):
+        sys.__stdout__.write(s+'\n')
+        sys.__stdout__.flush()
+
+    def _check_mp_mode(self):
+        """check multiprocess and switch to que if necessary"""
+        if not self._found_newprocess.value:
+            if not self._is_master_process():
+                self._found_newprocess.value = True
+        elif self._found_newprocess.value and not self._master_has_switched:
+
+            #switch to que if it has not been switch
+            if self._is_master_process():
+                self._switch_to_que()
+                self._master_has_switched = True
+
+        return self._found_newprocess.value
+
 
     def set_parent(self, parent):
         self.parent_header = extract_header(parent)
@@ -38,20 +82,33 @@ class OutStream(object):
 
     def flush(self):
         #io.rprint('>>>flushing output buffer: %s<<<' % self.name)  # dbg
+
         if self.pub_socket is None:
             raise ValueError(u'I/O operation on closed file')
         else:
-            data = self._buffer.getvalue()
-            if data:
-                content = {u'name':self.name, u'data':data}
-                msg = self.session.send(self.pub_socket, u'stream', content=content,
-                                       parent=self.parent_header, ident=self.topic)
-
-                if hasattr(self.pub_socket, 'flush'):
-                    # socket itself has flush (presumably ZMQStream)
-                    self.pub_socket.flush()
-                self._buffer.close()
-                self._new_buffer()
+            if self._is_master_process():
+                data = u''
+                #obtain data
+                if self._check_mp_mode():#multiprocess
+                    with self._que_lock:
+                        while not self._que_buffer.empty():
+                            data += self._que_buffer.get()
+                else:#single process mode
+                    data = self._buffer.getvalue()
+
+                if data:
+                    content = {u'name':self.name, u'data':data}
+                    msg = self.session.send(self.pub_socket, u'stream', content=content,
+                                           parent=self.parent_header, ident=self.topic)
+
+                    if hasattr(self.pub_socket, 'flush'):
+                        # socket itself has flush (presumably ZMQStream)
+                        self.pub_socket.flush()
+                    self._buffer.close()
+                    self._new_buffer()
+            else:
+                pass
+
 
     def isatty(self):
         return False
@@ -76,7 +133,12 @@ class OutStream(object):
             if not isinstance(string, unicode):
                 string = string.decode(self.encoding, 'replace')
 
-            self._buffer.write(string)
+            if self._check_mp_mode(): #multi process mode
+                with self._que_lock:
+                    self._que_buffer.put(string)
+            else: #sigle process mode
+                self._buffer.write(string)
+
             current_time = time.time()
             if self._start <= 0:
                 self._start = current_time