Merge pull request #123 from thomasj02/output_locking

Add locking around output buffer

ipykernel/iostream.py

@@ -9,6 +9,7 @@
 import os
 import threading
 import sys
+import threading
 import uuid
 import warnings
 from io import StringIO, UnsupportedOperation
@@ -222,6 +223,7 @@ def __init__(self, session, pub_thread, name, pipe=None):
         self._flush_lock = threading.Lock()
         self._flush_timeout = None
         self._io_loop = pub_thread.io_loop
+        self._buffer_lock = threading.Lock()
         self._new_buffer()
 
     def _is_master_process(self):
@@ -314,7 +316,8 @@ def write(self, string):
                 string = string.decode(self.encoding, 'replace')
 
             is_child = (not self._is_master_process())
-            self._buffer.write(string)
+            with self._buffer_lock:
+                self._buffer.write(string)
             if is_child:
                 # newlines imply flush in subprocesses
                 # mp.Pool cannot be trusted to flush promptly (or ever),
@@ -333,12 +336,13 @@ def writelines(self, sequence):
 
     def _flush_buffer(self):
         """clear the current buffer and return the current buffer data"""
-        data = u''
-        if self._buffer is not None:
-            buf = self._buffer
-            self._new_buffer()
-            data = buf.getvalue()
-            buf.close()
+        with self._buffer_lock:
+            data = u''
+            if self._buffer is not None:
+                buf = self._buffer
+                self._new_buffer()
+                data = buf.getvalue()
+                buf.close()
         return data
 
     def _new_buffer(self):