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gh-139653: Add PyUnstable_ThreadState_SetStack() #139668

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@vstinner vstinner commented Oct 6, 2025 •
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Add PyUnstable_ThreadState_SetStack() and
PyUnstable_ThreadState_ResetStack() functions to set the stack base address and stack size of a Python thread state.

📚 Documentation preview 📚: https://cpython-previews--139668.org.readthedocs.build/

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pythongh-139653: Add PyUnstable_ThreadState_SetStack()
7a0b713 
Add PyUnstable_ThreadState_SetStack() and
PyUnstable_ThreadState_ResetStack() functions to set the stack base
address and stack size of a Python thread state.
@bedevere-app bedevere-app bot mentioned this pull request Oct 6, 2025
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encukou commented Oct 6, 2025

This generally matches what I came up with :)

The start argument might be confusing, as the place usage grows towards.
Why not use bottom & top as in the internals?

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vstinner commented Oct 6, 2025

This generally matches what I came up with :)

Good!

The start argument might be confusing, as the place usage grows towards. Why not use bottom & top as in the internals?

APIs like make_fcontext() or sigaltstack() use void *stack_start_address and size_t stack_size.

pthread_attr_setstack() and pthread_attr_getstack() also use void *stack_start_address and size_t stack_size.

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vstinner commented Oct 6, 2025
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Doc/c-api/init.rst
.. versionadded:: next
.. c:function:: void PyUnstable_ThreadState_ResetStack(PyThreadState *tstate)
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I'm not sure of this name. Maybe PyUnstable_ThreadState_InitStack() would be more explicit?

vstinner
vstinner commented Oct 6, 2025
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Python/ceval.c
assert(ts->c_stack_soft_limit < ts->c_stack_top);

// Test the stack pointer
#if !defined(NDEBUG) && !defined(__wasi__)
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These assertions fail on WASI but I don't have time right now to investigate why.

@vstinner vstinner marked this pull request as ready for review October 6, 2025 21:35
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vstinner commented Oct 6, 2025

cc @markshannon @zooba

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