[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[STINNER Victor]

STINNER Victor  added the comment:

> This is great -- thank you for handling this so quickly.

Thanks for testing the master branch and reporting regressions quickly as well 
;-)

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Wenzel Jakob]

Wenzel Jakob  added the comment:

This is great -- thank you for handling this so quickly.

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Ned Deily]

Change by Ned Deily :


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keywords:  -3.8regression
versions:  -Python 3.8

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[STINNER Victor]

STINNER Victor  added the comment:

> Since this sounds like a regression being introduced by 3.8.0, should the 
> reversion be included in 3.8.0 final or can it wait for 3.8.1?

Oh, in fact, the change was only made in the master branch: after the 3.8 
branch was created. The 3.8 branch still contains PyThreadState_DeleteCurrent() 
;-) There is no regression in 3.8, only in master, and the regression in master 
has been fixed.

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priority: release blocker -> 
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 8855e47d09d4db1206c65b24efc8ad0df585ac46 by Victor Stinner 
(Joannah Nanjekye) in branch 'master':
bpo-38266: Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal 
(GH-16558)
https://github.com/python/cpython/commit/8855e47d09d4db1206c65b24efc8ad0df585ac46


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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[STINNER Victor]

STINNER Victor  added the comment:

> Since this sounds like a regression being introduced by 3.8.0, should the 
> reversion be included in 3.8.0 final or can it wait for 3.8.1?

IMHO PR 16558 is safe: it adds code which already existed in Python 2.7, and 
likely previously. For me it's a low risk of regression between rc1 and final.

I set the priority to release blocker, but Lukasz is the last one to take the 
final decision on including the fix or not.

Well, right now, I don't consider that PR 16558 is ready to be merged.

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Ned Deily]

Ned Deily  added the comment:

Since this sounds like a regression being introduced by 3.8.0, should the 
reversion be included in 3.8.0 final or can it wait for 3.8.1?

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keywords: +3.8regression
nosy: +lukasz.langa, ned.deily

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Joannah Nanjekye]

Change by Joannah Nanjekye :


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keywords: +patch
pull_requests: +16148
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/16558

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Eric Snow]

Eric Snow  added the comment:

@Joannah, sounds good.  Thanks!

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Eric Snow]

Eric Snow  added the comment:

I *was* going to suggest that we also put an underscore prefix on the name, but 
I couldn't think of a reason why we would want to discourage use (other than to 
reduce the size of the [supported] public API).  Moving it to 
Include/cpython/pystate.h is probably enough.

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[STINNER Victor]

STINNER Victor  added the comment:

If we want to make the function "fully public", I suggest to write 
documentation and have a simple unit test.

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Joannah Nanjekye]

Joannah Nanjekye  added the comment:

I will handle this later today.

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Joannah Nanjekye]

Joannah Nanjekye  added the comment:

+1 for moving from Include/pystate.h to Include/cpython/pystate.h

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Eric Snow]

Eric Snow  added the comment:

s/un-revert/revert/

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Eric Snow]

Eric Snow  added the comment:

FWIW, when we un-revert we should be sure to move PyThreadState_DeleteCurrent() 
from Include/pystate.h to Include/cpython/pystate.h.  (I suppose that could be 
done in a separate PR to keep the git history clear.)

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Eric Snow]

Eric Snow  added the comment:

FWIW, I support reverting the removal of PyThreadState_DeleteCurrent().  We 
only reverted under the assumption that no one was using this function.  
Clearly we were mistaken. :)

I'll re-open #37878 to revive the discussion about documenting the function 
(which we still may or may not want to do).

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Joannah Nanjekye]

Joannah Nanjekye  added the comment:

I am okay with the revert but @victor may still have some reservations on this.

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[issue38266] Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal

[Wenzel Jakob]

New submission from Wenzel Jakob :

A commit from a few days ago and discussed in issue #37878 removed an 
undocumented function PyThreadState_DeleteCurrent() from Python's public API.

This function was exposed for good reasons and simply removing it because it is 
undocumented strikes me as a somewhat brutal solution to achieve documentation 
coverage. This function is useful -- even essential -- to delete the current 
thread's thread state, which cannot be done using the still-public 
PyThreadState_Delete(). The documentation could simply be a line stating this 
explicitly.

I was asked to provide an example of an actual usage: this function is used by 
pybind11, which is a widely used library for creating Python bindings to C++ 
code. pybind11 only calls PyThreadState_DeleteCurrent() in a rare set of 
circumstances, but there is no alternative in this case. Specifically, pybind11 
can intercept a Python function call on the main() thread and delete the 
associated thread state, launching a new thread and continuing Python execution 
there (with a newly created thread state).

Kind of crazy, so why is this useful? The answer is UI libraries. On some 
platforms, it is not legal to poll UI events on any thread other than the main 
thread. This means that it's impossible to implement a proper asynchronous UI 
event loop because Python is hogging the main thread. With the functionality in 
pybind11's gil_scoped_acquire, it is possible can launch an event polling loop 
on the main thread, continue running an interactive Python REPL on another 
thread, and even swap them back e.g. when the user interface is no longer 
needed.

Best,
Wenzel

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components: Interpreter Core
messages: 353114
nosy: eric.snow, nanjekyejoannah, ncoghlan, tcaswell, vstinner, wenzel
priority: normal
severity: normal
status: open
title: Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal
type: behavior
versions: Python 3.8, Python 3.9

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