New submission from Jason Madden <ja...@nextthought.com>:
Using Python 2.7.15, if a BufferedWriter wraps an IO object that duplicates the
memoryview passed to the IO object's `write` method, that memoryview leaks.
This script demonstrates the problem by leaking a memoryview for each iteration
of the loop (if the `flush` is skipped, the leaks are less frequent but still
occur):
```
from __future__ import print_function
import io
import gc
def count_memoryview():
result = 0
for x in gc.get_objects():
if type(x) is memoryview:
result += 1
return result
class FileLike(object):
closed = False
def writable(self):
return True
def write(self, data):
memoryview(data) # XXX: This causes the problem
return len(data)
bf = io.BufferedWriter(FileLike())
i = 0
memoryview_count = 0
while True:
if i == 0 or i % 100 == 0:
# This reports 100 new memoryview objects each time
old = memoryview_count
new = count_memoryview()
print(i, "memoryview", new, "+%s" % (new - old))
memoryview_count = new
bf.write(b"test")
bf.flush()
i += 1
```
The leak can also be observed using the operating system's memory monitoring
tools for the process (seen on both Fedora and macOS).
Commenting out the line in `FileLike.write` that makes a duplicate memoryview
of the given buffer solves the leak.
Deleting the BufferedWriter doesn't appear to reclaim the leaked memoryviews.
I can't duplicate this in Python 3.4 or above.
Originally reported to gevent in https://github.com/gevent/gevent/issues/1318
Possibly related to Issue 26720 and Issue 15994
----------
components: IO
messages: 330206
nosy: jmadden
priority: normal
severity: normal
status: open
title: duplicate of memoryview from io.BufferedWriter leaks
versions: Python 2.7
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue35291>
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