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GeezerVison is showing github.com — gh-78502: Add a trackfd parameter to mmap.mmap() on Windows by serhiy-storchaka · Pull Request #138238 · python/cpython

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@serhiy-storchaka

@serhiy-storchaka serhiy-storchaka commented Aug 29, 2025 •
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If trackfd is False, the file handle corresponding to fileno will not be duplicated.

  • Issue: mmap.mmap() should not necessarily clone the file descriptor #78502

📚 Documentation preview 📚: https://cpython-previews--138238.org.readthedocs.build/

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@serhiy-storchaka
pythongh-78502: AAdd a trackfd parameter to mmap.mmap() on Windows
d1ce256 
If trackfd is False, the file handle corresponding to fileno
will not be duplicated.
@serhiy-storchaka
serhiy-storchaka requested review from encukou and zooba August 29, 2025 09:15
@serhiy-storchaka
serhiy-storchaka requested a review from AA-Turner as a code owner August 29, 2025 09:15
@bedevere-app bedevere-app Bot added the awaiting core review label Aug 29, 2025
@bedevere-app bedevere-app Bot mentioned this pull request Aug 29, 2025
mmap.mmap() should not necessarily clone the file descriptor #78502
Closed
@serhiy-storchaka
pythongh-78502: AAdd a trackfd parameter to mmap.mmap() on Windows
558beef 
If trackfd is False, the file handle corresponding to fileno
will not be duplicated.
@serhiy-storchaka
serhiy-storchaka force-pushed the mmap-trackfd-win branch from d1ce256 to 558beef Compare August 29, 2025 15:47
@serhiy-storchaka serhiy-storchaka added the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label Aug 29, 2025
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bedevere-bot commented Aug 29, 2025

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🤖 New build scheduled with the buildbot fleet by @serhiy-storchaka for commit 558beef 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F138238%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.
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@bedevere-bot bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label Aug 29, 2025
@serhiy-storchaka serhiy-storchaka changed the title gh-78502: AAdd a trackfd parameter to mmap.mmap() on Windows gh-78502: Add a trackfd parameter to mmap.mmap() on Windows Aug 29, 2025
encukou
encukou approved these changes Sep 1, 2025
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I'm not much of a Windows expert, but, the code looks good to me! Thank you!

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Sep 1, 2025
zooba
zooba reviewed Sep 1, 2025
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Other than that condition, looks fine to me.

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Comment thread Modules/mmapmodule.c Outdated

#ifdef MS_WINDOWS
if (self->file_handle != INVALID_HANDLE_VALUE) {
if (self->file_handle != INVALID_HANDLE_VALUE || !self->trackfd) {

@zooba zooba Sep 1, 2025

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I don't like combining an error condition check with a state check like this, it gives us a way to call GetFileSize(INVALID_HANDLE_VALUE, ...).

Maybe this should be && self->trackfd instead?

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@serhiy-storchaka serhiy-storchaka Sep 2, 2025

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They both are state checks. The behavior is consistent with Posix -- if trackfd is false, we get an OSError. We could raise a different error, but then we need to change the Posix code too. Is it fine to do this in this PR, or better open a separate PR?

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@zooba zooba Sep 2, 2025 •
edited
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We should never deliberately pass INVALID_HANDLE_VALUE to a Win32 API, but we might in this case because of the or condition.

If trackfd is false, we should just raise an error directly, rather than relying on the OS to generate an error code for us.

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@vstinner vstinner Sep 2, 2025

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If trackfd is false, we should just raise an error directly, rather than relying on the OS to generate an error code for us.

I agree with that.

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serhiy-storchaka added 2 commits September 2, 2025 17:40
@serhiy-storchaka
Merge remote-tracking branch 'refs/remotes/origin/mmap-tracefd-win' i…
55359e0 
…nto mmap-trackfd-win
@serhiy-storchaka
Merge branch 'main' into mmap-trackfd-win
3a37550
vstinner
vstinner approved these changes Sep 2, 2025
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LGTM

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Comment thread Modules/mmapmodule.c Resolved

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Comment thread Modules/mmapmodule.c Outdated

#ifdef MS_WINDOWS
if (self->file_handle != INVALID_HANDLE_VALUE) {
if (self->file_handle != INVALID_HANDLE_VALUE || !self->trackfd) {

@vstinner vstinner Sep 2, 2025

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If trackfd is false, we should just raise an error directly, rather than relying on the OS to generate an error code for us.

I agree with that.

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serhiy-storchaka and others added 2 commits September 2, 2025 18:43
@serhiy-storchaka
Raise ValueError for size() with trackfd=False.
0ee3c86
@serhiy-storchaka @vstinner
Update Modules/mmapmodule.c
ea85b30 
Co-authored-by: Victor Stinner <[email protected]>
@serhiy-storchaka

serhiy-storchaka commented Sep 2, 2025

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Before merging this PR, it would be convenient to merge #24781.
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@serhiy-storchaka serhiy-storchaka mentioned this pull request Sep 2, 2025
mmap.size() raises OSError on Unix for anonymous memory #87595
Closed
@serhiy-storchaka
Merge branch 'main' into mmap-trackfd-win
ebcb3e3
@serhiy-storchaka
serhiy-storchaka merged commit 7274d07 into python:main Sep 3, 2025
@bedevere-app bedevere-app Bot removed the awaiting merge label Sep 3, 2025
@serhiy-storchaka
serhiy-storchaka deleted the mmap-trackfd-win branch September 3, 2025 08:31
lkollar pushed a commit to lkollar/cpython that referenced this pull request Sep 9, 2025
@serhiy-storchaka @lkollar
pythongh-78502: Add a trackfd parameter to mmap.mmap() on Windows (py…
1a3e61d 
…thonGH-138238)

If trackfd is False, the file handle corresponding to fileno
will not be duplicated.
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@zooba zooba zooba left review comments
@vstinner vstinner vstinner approved these changes
@encukou encukou encukou approved these changes
@AA-Turner AA-Turner Awaiting requested review from AA-Turner AA-Turner is a code owner

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@serhiy-storchaka @bedevere-bot @vstinner @encukou @zooba
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