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gh-120608: Make reversed thread-safe #120609

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gh-120608: Make reversed thread-safe #120609

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Make reversed thread-safe
eendebakpt Jun 16, 2024
40018a1
Add Py_EXIT_CRITICAL_SECTION
eendebakpt Jun 16, 2024
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📜🤖 Added by blurb_it.
blurb-it[bot] Jun 16, 2024
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Update Misc/NEWS.d/next/Core and Builtins/2024-06-16-22-42-47.gh-issu…
eendebakpt Jun 17, 2024
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Add Py_EXIT_CRITICAL_SECTION
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@eendebakpt
eendebakpt committed Jun 16, 2024
commit 40018a179253487c2f1cc426051c84beb21e817f
3 changes: 3 additions & 0 deletions Include/internal/pycore_critical_section.h
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Expand Up @@ -98,6 +98,8 @@ extern "C" {
# define Py_END_CRITICAL_SECTION() \
_PyCriticalSection_End(&_cs); \
}
# define Py_EXIT_CRITICAL_SECTION() \
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@sobolevn sobolevn Jun 17, 2024

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Maybe it is better to define a local API instead of a global one? For example END_TYPE_LOCK() does that.

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@erlend-aasland erlend-aasland Jun 17, 2024

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You can just extract the critical section into a helper function and then wrap the helper with the existing macros.

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@erlend-aasland erlend-aasland Jun 17, 2024 •
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For this PR, I'd just extract most of reversed_next into a reversed_next_impl and wrap that with the Py_{BEGIN,END}_CRITICAL_SECTION macros. See also #120318.

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@lysnikolaou lysnikolaou Jun 17, 2024

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FWIW we ended up not doing that in #120318. There's this comment though that explains the approach and gives an example.

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@eendebakpt eendebakpt Jun 17, 2024

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Thanks for the feedback everyone! I added the Py_EXIT_CRITICAL_SECTION in this PR (and some others) to deal with return and goto statements. I am not in favor of adding a local API, since it will leak details of the locking implementation to modules. Changing the Py_EXIT_CRITICAL_SECTION to a more private _Py_EXIT_CRITICAL_SECTION (or something like that) would be fine with me.

In this case we can indeed refactor to create a reversed_next_impl and put a global lock around it. I am not too worried about performance here, and if it turns out performance is an issue we can change later.

Unless more suggestions come it, I will refactor to reversed_next_impl in the coming days.

_PyCriticalSection_End(&_cs);

# define Py_BEGIN_CRITICAL_SECTION2(a, b) \
{ \
Expand Down Expand Up @@ -156,6 +158,7 @@ extern "C" {
# define Py_BEGIN_CRITICAL_SECTION(op)
# define Py_END_CRITICAL_SECTION()
# define Py_BEGIN_CRITICAL_SECTION2(a, b)
# define Py_EXIT_CRITICAL_SECTION()
# define Py_END_CRITICAL_SECTION2()
# define Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(original)
# define Py_END_CRITICAL_SECTION_SEQUENCE_FAST()
Expand Down