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Avoid thread termination in scoped_released #2657

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Merged
henryiii merged 9 commits into from
Dec 19, 2020
Merged

Avoid thread termination in scoped_released #2657

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7e8a4cf
Avoid thread termination in scoped_released
malfet Nov 13, 2020
9e8bd73
Simplify _Py_IsFinalizing() availability check
malfet Nov 13, 2020
c82145d
Fix typo
malfet Nov 17, 2020
7b70787
Add version agnostic `detail::finalization_guard()`
malfet Nov 17, 2020
461e81a
Move `finalization_guard` to detail/common.h
malfet Nov 17, 2020
f5804e3
Move `is_finalizing()` back to pybind11.h
malfet Nov 17, 2020
e5fe8d3
Simplify `is_finalizing()` check
malfet Nov 18, 2020
bb8cee6
feat: disarm
henryiii Dec 16, 2020
93639b8
docs: fix comment
henryiii Dec 18, 2020
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12 changes: 12 additions & 0 deletions include/pybind11/pybind11.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2121,7 +2121,12 @@ class gil_scoped_acquire {
pybind11_fail("scoped_acquire::dec_ref(): internal error!");
#endif
PyThreadState_Clear(tstate);
#if (PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION > 6) && !defined(Py_LIMITED_API)
if (!_Py_IsFinalizing())
PyThreadState_DeleteCurrent();
#else
PyThreadState_DeleteCurrent();
#endif
PYBIND11_TLS_DELETE_VALUE(detail::get_internals().tstate);
release = false;
}
Expand Down Expand Up @@ -2153,7 +2158,14 @@ class gil_scoped_release {
~gil_scoped_release() {
if (!tstate)
return;
#if (PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION > 6) && !defined(Py_LIMITED_API)
// PyEval_RestoreThread() should not be called if runtime is finilizing
// See https://docs.python.org/3/c-api/init.html#c.PyEval_RestoreThread
if (!_Py_IsFinalizing())
PyEval_RestoreThread(tstate);
#else
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@rwgk rwgk Nov 14, 2020

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Minor: typo: finilizing

More significantly: I think the code could be made more readable and maintainable by centralizing the #if #else #endif in a, e.g., detail::finalization_guard() inline helper function, so that there is a formal link to the comment from both places, and less preprocessor clutter.

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@YannickJadoul YannickJadoul Nov 14, 2020

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Sure that that's not just going to add more confusion, to have another indirection? As long as it's just these two (very related) spots, to me, this seem reasonably fine? (We currently have these kinds of things inline in other places as well, and this should make it easy to remove once we drop <= 3.6?)

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@henryiii henryiii Nov 15, 2020

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The practical version of DRY/SPOT that I've seen states that exactly one duplication is allowed, if it's clearly more complex to combine it. Trying to take DRY/SPOT to the extreme of truly one point of truth for all code can impose an unmanageable level of complexity, so allowing it to be relaxed by one at programmer discretion balances the ideal with practicality. (and if there's more than one duplication, the extra complexity is always worth it).

In short, I'm fine either way.

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@rwgk rwgk Nov 15, 2020

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Thanks Henry! I hadn't heard of DRY/SPOT before, good to know there is something to refer to.

In this particular case I'm not so much concerned about the code duplication, but mostly about the comment only appearing in one place. For someone arriving at the second place from some completely different context, they will not even know the comment exists in the other place, and may miss it. But if they get curious about detail::finalization_guard(), they are guaranteed to find the comment.

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@YannickJadoul YannickJadoul Nov 15, 2020

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The comment is true, though! I completely agree there. There should at least be a "see a few lines up/down, at ...".

Apart from that, I don't feel too strongly, so up to @malfet AFAIC, but I just though the #if SOME_PYTHON_VERSION pattern exists inline in lots of places of code.
And it's kind of hard to capture what it's doing (i.e., finalization_guard doesn't really describe what's happening) ?

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@malfet malfet Nov 17, 2020

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Thank you for the feedback. Fixed typo and moved and extended runtime finalization check to pybind11/detail/internals.h

PyEval_RestoreThread(tstate);
#endif
if (disassoc) {
auto key = detail::get_internals().tstate;
PYBIND11_TLS_REPLACE_VALUE(key, tstate);
Expand Down