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Add locking around output buffer #123

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Merged
minrk merged 3 commits into from
Apr 15, 2016
Merged

Add locking around output buffer #123

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215b8c3
Add locking around output buffer to fix https://github.com/ipython/ip…
thomasj02 Apr 14, 2016
6c9decf
Add _ to conform to code style
thomasj02 Apr 14, 2016
26a12db
Use 'with' for locking
thomasj02 Apr 15, 2016
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7 changes: 7 additions & 0 deletions ipykernel/iostream.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@
import os
import threading
import sys
import threading
import uuid
import warnings
from io import StringIO, UnsupportedOperation
Expand Down Expand Up @@ -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):
Expand Down Expand Up @@ -314,7 +316,9 @@ def write(self, string):
string = string.decode(self.encoding, 'replace')

is_child = (not self._is_master_process())
self._buffer_lock.acquire(True)
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@minrk minrk Apr 14, 2016

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you can use with self._buffer_lock in both places

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@takluyver takluyver Apr 14, 2016

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To expand a bit: if the code between acquire() and release() throws an error for some reason, the lock would never be released. You can make sure that some 'after' code is run even if an exception is thrown:

lock.acquire()
try:
    do_stuff()
finally:
    lock.release()

But locks support a more convenient way to achieve the same thing:

with lock:
    do_stuff()

self._buffer.write(string)
self._buffer_lock.release()
if is_child:
# newlines imply flush in subprocesses
# mp.Pool cannot be trusted to flush promptly (or ever),
Expand All @@ -333,12 +337,15 @@ def writelines(self, sequence):

def _flush_buffer(self):
"""clear the current buffer and return the current buffer data"""

self._buffer_lock.acquire(True)
data = u''
if self._buffer is not None:
buf = self._buffer
self._new_buffer()
data = buf.getvalue()
buf.close()
self._buffer_lock.release()
return data

def _new_buffer(self):
Expand Down