Description

fowczarek

opened on Feb 4, 2025

Issue body actions

Bug report

Bug description:

During debugging memory buildup, I've noticed gzip.GzipFile holds a reference to itself (Cycle: GzipFile._buffer->BufferedWriter._raw->_WriteBufferStream.gzip_file-> GzipFile). This cycle prevents memory from being freed until the garbage collector runs a deep cleanup cycle (generation=2).

Steps to reproduce

1. Disable garbage collection temporarily to make sure we are the ones who catch it
2. Set the garbage collector's debug level to DEBUG_LEAK
3. Open GzipFile.
4. Force garbage collection and look at its output

import gc
import gzip
import io

gc.collect()
gc.disable()
gc.set_debug(gc.DEBUG_LEAK)

with io.BytesIO() as buffer:
    with gzip.GzipFile(mode="wb", fileobj=buffer):
        pass

gc.collect()
gc.set_debug(0)

Potential solution

class _WriteBufferStream(io.RawIOBase):
    ...

    def __del__(self):
        del self.gzip_file

CPython versions tested on:

3.12

Operating systems tested on:

macOS

Linked PRs

• gh-129640: Add tests for reference cycle in gzip.GzipFile #130916

Reacted by Iga Karbowiak, Patryk Zawadzki, Jakub and Przemysław Łada

Activity

1. fowczarek

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Feb 4, 2025
2. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Feb 4, 2025
3. Mr-Sunglasses

   added a commit that references this issue on Mar 6, 2025

   pythongh-129640: Fix reference cycle in `gzip.GzipFile`

   06999db
4. cmaloney commented on Mar 7, 2025

   

   cmaloney

   on Mar 7, 2025

   Contributor

   More actions

   I think this is the equivalent to gh-129726? (Hadn't seen this issue until just now). If so, has a fix which has been backported to 3.12. Similar concept, but broke refloop by adding a weakref (PR: #130055)

   Reacted by Shantanu, Kanishk Pachauri and Filip Owczarek
5. Mr-Sunglasses commented on Mar 8, 2025

   

   Mr-Sunglasses

   on Mar 8, 2025

   Contributor

   More actions

   This Issue is fixed in (PR: #130055) by @cmaloney . The (PR: #130916) add's some tests for it.

   Reacted by Cody Maloney and Filip Owczarek
6. hauntsaninja commented on Mar 9, 2025

   

   hauntsaninja

   on Mar 9, 2025

   Contributor

   More actions

   Additional test PRs still welcome, but going ahead and closing this since the issue is resolved by #130055 (and backported)

   Reacted by Cody Maloney
7. hauntsaninja

   closed this as completedon Mar 9, 2025

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