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[WIP] Add SemLock implementation to RustPython #6506

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Copilot AI commented Dec 25, 2025 •
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  • Establish baseline by running targeted existing tests to observe current failures
  • Implement _multiprocessing.SemLock and sem_unlink functionality (Unix-focused, preserving Windows behavior)
  • Add or adapt focused tests to cover basic SemLock creation and acquire/release
  • Run targeted tests for _multiprocessing/multiprocessing synchronization and verify behavior
  • Final review, code cleanup, and security checks
Original prompt

This section details on the original issue you should resolve

<issue_title>_multiprocessing_SemLock</issue_title>
<issue_description>This is missing in RustPython.</issue_description>

<agent_instructions>Checkout SemLock in CPython and implement one for RustPython</agent_instructions>

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@youknowone
Changes before error encountered
b7fcc92 
Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>
Copilot AI requested a review from youknowone December 25, 2025 02:14
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youknowone commented Dec 25, 2025

@copilot try again

@youknowone
Implement Unix SemLock and expose sem_unlink
ec25df2 
Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>
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Copilot AI commented Dec 25, 2025

@copilot try again

Implemented Unix _multiprocessing.SemLock (with constants and sem_unlink) and ran rustpython-stdlib tests in ec25df2.

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youknowone commented Dec 25, 2025

@copilot fix CI failure

error[E0425]: cannot find function `sem_getvalue` in crate `libc`
   --> crates/stdlib/src/multiprocessing.rs:308:38
    |
308 |             let res = unsafe { libc::sem_getvalue(self.handle.as_ptr(), &mut value) };
    |                                      ^^^^^^^^^^^^ not found in `libc`

error[E0425]: cannot find function `sem_timedwait` in crate `libc`
    --> crates/stdlib/src/multiprocessing.rs:387:42
     |
 387 |                 let res = unsafe { libc::sem_timedwait(self.handle.as_ptr(), &ts) };
     |                                          ^^^^^^^^^^^^^ help: a function with a similar name exists: `sem_trywait`
     |
    ::: /Users/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.178/src/unix/mod.rs:1550:5
     |
1550 |     pub fn sem_trywait(sem: *mut sem_t) -> c_int;
     |     --------------------------------------------- similarly named function `sem_trywait` defined here

@youknowone
Fix missing sem_* symbols on libc targets
aa11f3e 
Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>
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Copilot AI commented Dec 25, 2025

@copilot fix CI failure

...

Added explicit extern bindings for sem_getvalue/sem_timedwait so CI builds succeed across libc targets; rustpython-stdlib tests now pass (aa11f3e).

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youknowone commented Dec 25, 2025

@copilot Something wrong. Carefully review the CI result and fix the problem.

e.g.

Run target/release/rustpython -m test -j 1 -u all --slowest --fail-env-changed -v test__colorize test_array test_asyncgen test_binop test_bisect test_bool test_bytes test_call test_class test_cmath test_collections test_complex test_contains test_copy test_dataclasses test_decimal test_decorators test_defaultdict test_deque test_dict test_dictcomps test_dictviews test_dis test_enumerate test_exception_variations test_float test_format test_fractions test_genericalias test_genericclass test_grammar test_range test_index test_int test_int_literal test_isinstance test_iter test_iterlen test_itertools test_json test_keyword test_keywordonlyarg test_list test_long test_longexp test_math test_operator test_ordered_dict test_pow test_raise test_richcmp test_scope test_set test_slice test_sort test_string test_string_literals test_strtod test_structseq test_subclassinit test_super test_syntax test_tuple test_types test_unary test_unpack test_weakref test_yield_from

thread 'main' (4106) panicked at crates/stdlib/src/multiprocessing.rs:343:22:
intern RECURSIVE_MUTEX
stack backtrace:
   0:     0x55b58e7f3253 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h718e2d17a1928e63
   1:     0x55b58d63ea2f - core::fmt::write::h1d2246b072ea91eb
   2:     0x55b58e7c6ea3 - std::io::Write::write_fmt::haf55272405c09d9b
   3:     0x55b58e7cf6d2 - std::sys::backtrace::BacktraceLock::print::h61c3bd81a9458a03
   4:     0x55b58e7d27ae - std::panicking::default_hook::{{closure}}::haf1ffb5d1e33a97f
   5:     0x55b58e7d22ef - std::panicking::default_hook::hc32245deb6eaa988
   6:     0x55b58e7d2b95 - std::panicking::panic_with_hook::h43adc00fd0e494cb
   7:     0x55b58e7d299a - std::panicking::panic_handler::{{closure}}::h44391079756da3e7
   8:     0x55b58e7cf819 - std::sys::backtrace::__rust_end_short_backtrace::h934e1568393e5b8f
   9:     0x55b58e7ba36d - __rustc[d9b87f19e823c0ef]::rust_begin_unwind
  10:     0x55b58d649020 - core::panicking::panic_fmt::h62031895f6e012da
  11:     0x55b58d647ebb - core::option::expect_failed::h40dde8b63ee0f843
  12:     0x55b58dfbc382 - <rustpython_stdlib::multiprocessing::_multiprocessing::SemLock as rustpython_vm::class::PyClassImpl>::impl_extend_class::h82ef0c5c139008a2
  13:     0x55b58dfbf3d4 - rustpython_vm::class::PyClassImpl::extend_class::h06a341b4833469e9
  14:     0x55b58df6e5f8 - once_cell::imp::OnceCell<T>::initialize::{{closure}}::h14eb56b716e2e7f9
  15:     0x55b58db718cc - once_cell::imp::initialize_or_wait::h34fa2e290e5e2ed3
  16:     0x55b58df6bd82 - once_cell::imp::OnceCell<T>::initialize::h11c02bfa74ceb193

@youknowone
Fix SemLock constant interning to avoid panic
c91612c 
Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>
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Copilot AI commented Dec 25, 2025

@copilot Something wrong. Carefully review the CI result and fix the problem.

e.g.
...

Switched SemLock constants to use ctx.intern_str to avoid missing intern entries (panic fixed) and reran cargo test -p rustpython-stdlib --lib -- --nocapture successfully (c91612c).

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_multiprocessing_SemLock

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